Answer: The above question sort of encompasses a few different potential things and I’m not 100% sure which you’re asking so I’ll just cover them all.  First realize that one fuel that the brain cannot use is fatty acids, at least not directly.  This has led to the oft-stated belief that the brain can only use glucose. But this is incorrect as the brain has an alternative fat derived fuel which are ketones (or ketone bodies, the two major of which are beta-hydroxybutyrate and acetyl-acetate). 

Ketones are produced primarily in the liver (from the breakdown of fatty acids) and exist predominantly as an alternative fuel source for the brain (they can also be used by skeletal muscle) during periods of low-carbohydrate availability.  This probably was originally important during periods of complete starvation; now very low-carbohydrate diets (defined here as any diet containing less than 100 grams per day of carbohydrates) effectively ‘exploit’ this mechanism.

Now, on a carbohydrate based diet, the brain runs essentially on 100% glucose since ketones are generally not produced in significant amounts under those conditions (there are a couple of odd exceptions, one is following very long duration endurance exercise where a post-exercise ketosis can occur due to changes in fuel metabolism).  So what happens when you remove most or all carbohydrates from the diet?  Does the brain magically switch to using ketones?  For the most part, no.  Studies done way back when show that there is an adaptation phase that may last about 3 weeks while the brain ramps up its ability to use ketones for fuel.  

Even there, after that roughly 3 week period, the brain still only derives about 75% of its total fuel requirements (about 400 calories per day or thereabouts) from ketones; the other 25% come from glucose (which the body can produce through a variety of pathways that I won’t detail here; all of this is explained in excruciating detail in my first book The Ketogenic Diet).  Mind you, this is only relevant on a very low-carbohydrate diet.  Even if the brain could still use ketones on a carb-based diet they wouldn’t be produced in large enough amounts for it to be relevant.

So I think that answers at least part of your question: when first starting a low-carbohydrate diet, it takes the brain about 3 weeks to adapt to using ketones for fuel; even then it only gets about 75% of its total fuel from them.  This scans pretty well with what many experience on the diet, they don’t feel fantastic for the first 2-3 weeks of the diet (while they are adapting). Some of that, mind you, is related more to mineral intake than anything else (early studies found that sufficient intake of sodium, potassium and magnesium eliminated all of the fatigue and lethargy that occurred on very low carbohydrate diets).

But there is a related question that often comes up which has to do with switching back and forth between fuels (this is especially relevant for some cyclical ketogenic diets such as what’s described in The Ketogenic Diet or in my Ultimate Diet 2.0).  Here I am unaware of any research on the topic and most of what I have to say is just based on empirical evidence, what people have reported over the 15+ years they’ve been giving me feedback.

Certainly early in the diet there is often a period where the alternation of high and low carbs often causes some people distress, they get the same headaches and issues going from high-carbs back to low-carbs for a couple of weeks.  Probably just a function of ‘interrupting’ the adaptation to ketone metabolism in the brain and there might be some rationale to doing 2-3 straight weeks of a ketogenic diet prior to inserting refeeds or carb-loads.

At the same time, after more extended periods on the diet (perhaps 6-8 weeks), switching back and forth from a carb-based to a ketone-based brain metabolism seems to cause most people no problems. They can sort of drop in and out of ketosis (even throughout the day under certain conditions) and not really notice anything one way or the other.  Interestingly, even after extended periods off of a low-carbohydrate diet, most people don’t report the same early adaptation phase that they went through the first time on the diet; they go back onto a ketogenic diet and don’t notice anything.

This suggests to me that there is some type of long-term and/or almost permanent change in the brain in terms of its ability to use ketones for fuel with long-term exposure to them.  Again, I have exactly zero research to back this up; it’s just an observation.  But even there you’d still expect to see the same basic 75/25 split, just with an easier switching back to ketone metabolism after that initial adaptation phase.

Hope that answers your question.

What I want to discuss is a concept that I call ‘excluding the middle’ but which is more formally referred to as a logical fallacy called ‘the false dilemma‘,  the ‘either/or fallacy’ or a whole host of other things.  It’s something I see a lot in both Internetz articles and Internetz arguments.

In brief, people have a tendency to play this cute little game where a given situation can either be exactly one thing (their preference) or exactly one other thing where that other thing is some ludicrous stupid-ass extreme example that they use to attempt to prove their preference simply by how extreme (and dumb) it is.  But compared to something stupid, anything is better by comparison.

As an example, I am apparently quoted as having said that “…compared to the Standard American Diet, a diet of bug spray and skittles would be healthier.”   One extreme compared to another and the second is only better because of the awfulness of the first.  Except that I was joking…mostly.  In most arguments, the folks falling prey to this trap are not.

Now, whether or not this is just some aspect of human nature where we want things to be one thing or another, or because people are bad at making logical arguments or what I have no idea.  Nor do I really care.  It’s called a logical fallacy for a reason and I’m going to give you four explicit examples to try to get my point across.

But simply, life is not binary and most things comes in varying degrees of extreme and shades of gray.  As my favorite author once put it “The universe can count beyond two.”  He was using this statement in a different context (to point out that most things fall into a yes/no/maybe type of situation and there are rarely simply yes/no answers) but it applies here too.  Hopefully this little piece will help you count beyond two.

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The HIT Example

For those who live under a rock, HIT refers to High Intensity Training (not to the confusingly similarly named HIIT or High-Intensity Interval Training).  Developed by Arthur Jones (as much to market Nautilus equipment or anything else) but truly popularized by Mike Mentzer (who called it Heavy Duty training), HIT has more or less become synonymous with doing 1 set to failure of a given exercise (interestingly, Jone’s original HIT was not like this at all and was actually a fairly moderate volume of training).  Yes, there’s more to it. No, I’m not going into details here because it doesn’t matter.

But in arguments with HIT’ers, if you suggest doing more than one set, you typically see a great example of what I’m talking about.  Specifically, you will often see the statement to the effect of “If you’re going to do more than 1 set, why not do 10, or 20, or 80?”  HIT’ers see the world in two simple binary situations: either you stop at one set or you do as many sets as possible.

That is, they don’t seem to have considered that one could do say, 4-8 sets of an exercise.  That the options are just 1 and ‘all’.  And since 1 set is better than ‘all’ sets, clearly it’s the correct choice.

They are excluding the middle: It’s not as if you can’t do a moderate number of sets (say 4-8 or whatever number might be optimal) and the only options are 1 or ‘all of them’.

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The Clean Eater Example

The idea of eating ‘clean’ is one that runs rampant in the physique sports.  Simply stated, ‘eating clean’ means eating only unprocessed foods in the diet.  Well, except when it’s inconvenient, it’s always amusing watching rabid clean freaks rationalize foods that don’t fit their definition (Crystal Light comes to mind) while eliminating foods (such as dairy) which clearly do fit their definition.  And when you get into arguments with clean freaks and suggest that it’s not required to eat clean 100% of the time, you will often get a response to the effect of “I guess I could go binge on junk food and McDonald’s and pizza at every meal, sure.”

I’d note that clean freaks often include a ‘cheat day’ where they go out of their way to eat the most junk humanly possible, often to the point of making themselves sick.  As well, many fall into the trap whereby if even a gram of an ‘unclean’ food passes their lips, they have ruined their diet and must go binge on everything they can get their hands on.  They need to read A Guide to Flexible Dieting.

In the clean freak’s mind, there are two binary options: you either eat clean 100% or you’re eating nothing but junk food at every meal every day.  The idea that you might ‘eat clean’ (whatever those words mean to you) 80-90% of the time and include selective ‘unclean foods’ (whatever that means to you) the other 10-20% of the time is simply an inconceivable one to many.

They are excluding the middle: it’s clean 100% of the time (except when it’s not) or junk food 100% of the time, you can’t do anything in the middle.  Even though you clearly can.  And most do, and more probably should.

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The Paleo Diet Example

Arguing with rabid paleo folks is about the same as arguing with the clean eating crowd.  I can recall specific arguments where the suggestion that grains (which represent unholy evil to the paleo crew) can be part of an overall diet was met with the counter-argument of “I’d never eat a diet that is 80% carbs.” Or something to that effect.

That is, the paleo eater seems to see the world as one of two things: you are either a strict paleo eater consuming nothing but meats, veggies, fruits and other paleo-approved ™ foods (and I’d note here that the paleo folks are about as flexible with their definitions as the clean eaters, routinely rationalizing foods that they want to eat while ignoring others based on whim) or you’re living on nothing but refined grains.

It’s one or the other, if you’re not 100% paleo, you’re 100% at the other extreme.   Apparently that whole concept of an athletic diet where you eat lots of protein, fruits, vegetables AND some amount of grains is simply inconceivable.  Despite the fact that athletes and bodybuilders have done that for decades.

They are excluding the middle: your diet is either 100% paleo (except for the exceptions they justify) or you’re eating 80% refined grains.  There is no possible middle ground that they can conceptualize.

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The HIIT/LSD Example

Now I am talking about High-Intensity Interval Training along with the whole silly either-or argument that is going on in the world of conditioning and cardiovascular training (something I’ve written about at length in the Steady State vs. Interval Training series).   Basically, and this is mostly a marketing thing/a backlash to the over-emphasize on low-intensity cardio of previous years, folks have flip flopped and it’s all intervals all the time.

Coaches will argue to the effect of “I would never have an athlete do low intensity work, marathon runners have a poor power output” or something roughly to the effect.   You’ll see similar stupidity aimed at folks aiming to lose fat where the statement is something akin to “Hours of low intensity work burn off muscle.”  As if the only way to do aerobic work is by doing hours and hours of it every day.

Apparently 45-60 minutes of low intensity work can’t be done even if dieters and contest bodybuilders have done exactly that for about 30 years.  Nor can a mix of low intensity work (i.e. 2-3 sessions per week or more) plus some interval work (1-2 session).    Or some other mixture depending on your goals and needs.  You know, like just about every endurance athlete in the world.

They are excluding the middle: It’s either nothing but interval sessions at every workout OR you’re training for the Tour De France and doing 30 hours per week of aerobic work, you can’t do anything in the middle.

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Summing Up

Stop excluding the middle.

Answer: First a quick definition for anyone who isn’t familiar with the abbreviation: as discussed in the Comparing the Diets Series , a CKD refers to a cyclical ketogenic diet.  This is simply a diet that alternates between periods of very low-carbohydrate eating (typically 4-6 days) and very high-carbohydrate eating (1-3 days).  Dan Duchaine’s Bodyopus, Mauro DiPasquale’s Anabolic Diet and my own Ultimate Diet 2.0 are all examples of CKD’s.  My first book The Ketogenic Diet discusses CKD’s generally in mind-numbing detail.

Now back to the question: does ketosis negatively impact on cognitive function?  And the answer is one huge it depends.  Certainly early studies found that, in the short-term (first 1-3 weeks), low-carbohydrate diets tend to cause some problems.  For this reason short-term studies (usually a week long) tend to report decrements in a lot of things including cognitive performance.

Empirically, as well, many report fatigue, lethargy and a sort of mental ‘fog’ until they adapt to the diet (the brain adjusts to using ketones for fuel over those first 3 weeks).  I’d note that supplementing with sodium, potassium and magnesium seems to go a long way towards limiting or eliminating that feeling of fatigue.

So, for most I certainly wouldn’t recommend starting a very low-carbohydrate/ketogenic diet right before some major test or cognitive challenge.  Odds are it’s going to cause problems.

But what about someone who has adapted to being in ketosis. There there tends to be huge variance.  Some people are sort of neutral to it but I know of many who report far better brain functioning when they are in ketosis.  I couldn’t tell you the mechanism, this is just one of those self-reported things.  But it tends to be highly variable (and I can’t think of any studies that have examined cognitive performance after long-term adaptation to low-carbohydrate diets).

CKD’s add another complication, outside of some exercise research on Cyclical Ketogenic Diets and Endurance Performance that looked only at performance, I’m unaware of any work on CKD’s and cognitive performance.  I bring this up as some people do report changes switching back and forth between very low and very high carbohydrate intakes.

Quite in fact, many who find that they feel ‘great’ in ketosis feel a bit dopey or sleepy when they switch back to high carb intakes.  This is probably related to either blood glucose swings or a big increase in brain serotonin (which tends to cause lethargy and fatigue) but it does occur.

Similarly, some seem to go through at least a brief re-adaptation (in terms of fatigue, etc.) going back from high carbs to low-carbs.  Again, this is pretty variable, many people can switch back and forth from one extreme to the other and don’t seem to notice anything.  I have no idea why, just reports I’ve seen.

So back to the question, should you switch out of ketosis for your test?  It’s a hard question to answer and you’d have to think back to your previous switches from low- to high-carbs during the CKD.  If you find that you’re fully adapted to ketosis and function fine mentally, and that you get dopey going back to high-carbs, I’d probably suggest you stay on low-carbs through the test.

If you’re one of those people who don’t seem to have ever fully adapted to being in ketosis (they do exist), you might want to move back to at least moderate carbs a day or two before your test.  Unfortunately, there’s just too much variability for me to give you any advice beyond that.

Question: I have done a lot of study in diets and nutrition but to this day I have not been able to get any concrete evidence on what happens with excess protein in the body and I’m hoping you can help.

To make things simple, lets take a theoretical diet consisting of 5000 calories of pure protein for a 60kg, 175cm female.

Many people claim that excess protein will get wasted while others say that all excess calories eventually end up being stored as fat.

I have done my own research on the breakdown of protein into amino acids and I understood it as: some of the amino acids are wasted while others will go through the cycle of conversion and will still be used by the body for energy.

Answer: Ok, first things first.  The example given above is absurdly non-physiological.   The satiating power of protein would make such a high protein consumption impossible.  That is, 5000 calories of pure protein is 1250 grams of pure protein.  Can’t be done.  Beyond that, while the biochemical pathways for the conversion of protein to fat do exist in humans, the likelihood of it ever happening in any but the most absurdly non-physiological circumstances are effectively nil.

Let me put this in perspective.  Despite a lot of claims to the contrary, the actual conversion of carbohydrate to fat in humans under normal dietary conditions is small approaching insignificant (a topic I discussed at least briefly in Nutrient Intake, Nutrient Storage and Nutrient Oxidation).

Make no mistake, the conversion of carbs to fat (a process called de-novo lipogenesis or DNL) can happen but the requirements for it to happen significantly are fairly rare in humans under most conditions (to discuss this in detail would require a full article, interested readers can search Medline for work by Hellerstein or Acheson on the topic).

At least one of those is when daily carbohydrate intake is just massive, fulfilling over 100% of the daily maintenance energy requirements.  And only then when muscle glycogen is full.  For an average sized male you’re looking at 700-900 grams of carbohydrate daily for multiple days running.

Which means that the odds of protein being converted to fat in any quantitatively meaningful fashion is simply not going to happen.  Certain amino acids are processed to a great degree in the liver (as I discuss in The Protein Book) and this can produce glucose, ketones and a few other things.  But triglycerides (the storage form of ‘fat’) isn’t one of them.

I imagine that if protein were going to be converted to fat, it would first have to be converted to glucose and only if the amount produced were then in excess of daily maintenance requirements would there be conversion to fat.  But as noted above, this simply isn’t going to happen under any even reasonably normal circumstances. No human could eat enough protein on a daily basis for it to occur.

What will happen, as discussed in Nutrient Intake, Nutrient Storage and Nutrient Oxidation. is that amino acid oxidation (burning for energy) will go up somewhat although, as discussed in that article, it’s a slow process and isn’t complete.

So, as noted above, while the pathway exists for protein to be stored as fat, and folks will continue to claim that ‘excess protein just turns to fat’, it’s really just not going to happen under any sort of real-world situation.  Certainly we can dream up odd theoretical situations where it might but those won’t apply to 99.9% of real-world situations.

1. Macronutrients: nutrients consumed in large amounts (‘macro’ = large)
2. Micronutrients: nutrients consumed in small mounts (‘micro’ = small)

So macronutrient refers to protein, carbohydrates, fats and alcohol, those nutrients that, when they are consumed are generally consumed in gram or larger amounts.  The micronutrients refers to vitamins and minerals which are usually consumed in very small amounts (e.g. the DRI for Vitamin C is 60mg where 1mg is 1/1000th of a gram).  I’m not going to talk about micronutrients in this article and will only focus on the macronutrients, specifically protein, carbohydrate, fat and alcohol.

I’m also going to assume that you’re getting your nutrients through food and it’s going in through your mouth. Certainly nutrients can be given via infusion but this is usually done in a hospital setting (sometimes athletes will rehydrate and carb-load with IV fluids and glucose, mind you) and I’ll assume you’re not doing that.

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Digestive Efficiency and Your Poop

Clearly anything you eat has to go through the process of chewing, swallowing and into the stomach for digestion.  There a bunch of stuff happens where the nutrients are broken down to one degree or another.  And either they get absorbed (moving into special cells to be released into the bloodstream, or lymphatic system in the case of dietary fats) or not.  If you’re particularly interested in the digestion processes of the different macronutrients, I’d refer you to the specific articles:

A Primer on Dietary Fats Part 1 for fat digestion.
A Primer on Dietary Carbohydrates Part 1 for carb digestion.
What are Good Sources of Protein-Digestibility for protein digestion.

Nutrients that aren’t absorbed in the stomach move further down the intestine where in some cases (for example, certain fibers), they are digested by special bacteria and re-enter the bloodstream as short-chain fatty acids.  This is discussed in Fiber – It’s Nature’s Broom.

Nutrients that pass that stage eventually come out the other end in your poo and we needn’t talk about that much more. I’ll only note in this regards that digestive efficiency in humans is generally very high.  Fats are absorbed with about 97% efficiency (e.g. if you eat 100 grams fat, you’ll absorb 97 grams of them), animal source proteins are about 90-95%, vegetable source proteins can be in the 80% range and carbohydrates vary drastically depending on their form, fiber content, etc.  But for the most part, with the exception of high-fiber foods, you’re not losing a lot of calories in your poop.

I would note, having said more about poop than necessary at this point, that there appears to be slight differences (based on the gut bacteria present) in how efficiently individuals absorb calories from the diet but this only amounts to perhaps a 100 cal/day difference between the highest and lowest people.  OF course, in cases of specific disease where there is nutrient malabsorption, all these comments go out the window but I won’t talk about that here.  I’ll assume you have a normally functioning gut, etc.

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Fates of Ingested Nutrients: Oxidation or Storage

So what happens after nutrients get through the stomach and intestines and into the body?  Broadly speaking, there are two primary fates for nutrients at this point which are oxidation or storage.  A third that I should at least mention is that, under certain conditions, nutrients will sort of ‘sit’ in the bloodstream either causing problems there or eventually being excreted in the urine.  Outside of various pathophysiologies (e.g. runaway diabetes where glucose is lost in the urine in large amounts), the urine excretion route is generally minimal approaching insignificant and I won’t focus on it further here.

Oxidation simply refers to the direct burning of fuels for energy.  This can occur in the liver, skeletal muscle and a few others places and all 4 macronutrients can strictly speaking undergo oxidation after ingestion.  So fatty acids from dietary fat ingestion can be used to produce energy, carbohydrate can be burned off, a little appreciated fact is that under normal circumstances as much as half of all dietary protein ingested gets metabolized in the liver via a process called deamination with some of it simply being burned off for energy.

Storage should be fairly clear and the nutrients (with the exception of alcohol) can be ‘stored’ in the body for later use.  Carbohydrates can be stored as liver or muscle glycogen, under rare circumstances they are converted to and stored as fat.  Dietary fat is stored either in fat cells or can be stored within muscle as intra-muscular triglyceride (IMTG).  Under certain pathological conditions, fat gets stored in places it’s not supposed to go, a situation called ectopic fat storage.  In a very real sense there’s no true store of dietary protein although amino acids from protein digestion are used to make various proteins and hormones in the body. Skeletal muscle is, in essence, a ‘store’ of protein in the body.  There is no store of alcohol in the body.

Which is the segue into the only real point I have to make in this piece: as it turns out, the size of a nutrient’s store in the body is inversely related to the body’s propensity to oxidize it after ingestion.  This is especially true in terms of the size of the store relative to the amount consumed on a daily basis.

Put a little more clearly, the better the body’s ability to store a given nutrient, the less it tends to alter/increase oxidize that nutrient after ingestion.  And vice versa, the smaller the store in the body of a given nutrient relative to intake levels, the more likely the body is to oxidize that nutrient after ingestion.  I’ve shown the implications of this in the table below and will make comments about specific nutrients below that.

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Fat
Body fat stores are effectively unlimited as individuals reaching 1000 lbs (and 70-80% body fat) have demonstrated.  Even a relatively lean male at 180 lbs and 12% body fat is carrying 21 pounds of fat.  Each pound contains maybe 400 grams of actual stored fat and that means about 8500 grams of fat stored in the body.  Contrast this to a relatively high daily intake of perhaps 100-150 grams per day and you can see that the body’s store of fat is much much higher than what you eat on a day.  And most people aren’t 12% body fat.

But for the most part, ingested dietary fat has little impact on fat burning in the body; that is, when you eat dietary fat, your body doesn’t increase fat oxidation.  One exception is if an absolutely massive amount of fat (like 80 g) is consumed all at once but even then the effect is fairly mild.  Some specific fats, notably medium chain triglycerides, are somewhat of an exception to this; they are oxidized in the liver directly.  Rather, the primary controller of dietary fat oxidation in the body is how many carbohydrates you’re eating, which I’ll explain momentarily.

Carbohydrate
For carbohydrate, the body’s stores are relatively close to the daily intake.  A normal non-carb loaded person may store 300-400 grams of muscle glycogen, another 50 or so of liver glyogen and 10 or so in the bloodstream as free glucose.  So let’s say 350-450 grams of carbohydrate as a rough average.  On a relatively normal diet of 2700 calories, if a person eats the ‘recommended’ 60% carbs, that’s 400 grams.  So about the amount that’s stored in the body already.

For this reason, the body is extremely good at modulating carbohydrate oxidation to carbohydrate intake.  Eat more carbs and you burn more carbs (you also store more glycogen); eat less carbs and you burn less carbs (and glycogen levels drop).  This occurs for a variety of reasons including changing insulin levels (fructose, for example, since it doesn’t raise insulin, doesn’t increase carbohydrate oxidation) and simple substrate availability.  And, as it turns out, fat oxidation is basically inversely related to carbohydrate oxidation.

So when you eat more carbs, you burn more carbs and burn less fat; eat less carbs and you burn less carbs and burn more fat.  And don’t jump to the immediate conclusion that lowcarb diets are therefore superior for fat loss because lowcarb diets are also higher in fat intake (generally speaking).  You’re burning more fat, but you’re also eating more.  But that’s a topic that I’ve not only addressed previously on the site but may look at in more detail in a future article with this piece as background.

Protein
The body’s total protein stores (and note again that this isn’t a true store in the sense of body fat and glycogen) is maybe 10-15kg or so when you add it all up.  Which is pretty high compared to an average daily intake.  The DRI for protein is only about 50-60 grams per day for the average person and even folks eating 200-300 grams per day are still eating far less protein than stored.   Which is why protein oxidation rates can change with intake.

As I mentioned above, an under-appreciated fact is that about half of all ingested dietary protein is metabolized in the liver (details on this can be found in The Protein Book).  Some of it is oxidized for energy while others are converted into other things (including glucose and ketones) for use elsewhere.  But, protein oxidation rates do change in response to intake.  So, when protein intake goes up, oxidation will increase; when protein intake goes down, oxidation rates decrease.  This change isn’t immediate (as it more or less is for carbohydrates) and takes 3-9 days to occur but mis-understanding of this process has led to some goofy ideas such as protein cycling.

But it also explains one other issue of importance to protein which has to do with speed of digestion. Early studies, including the oft-cited study on whey and casein by Boirie find that fast proteins are burned off for energy to a greater degree than slower digesting proteins.  Since the body doesn’t have anywhere to store the rapidly incoming amino acids, it simply burns off more for energy.  This, along with differences in handling (e.g. the fact that fast proteins are absorbed by the gut as discussed in Casein Hydrolysate and Anabolic Hormones and Growth – Research Review) are a big part of why slower digesting proteins invariably lead to better overall protein retention in the body; not only does more make it into the bloodstream but less is burned for fuel.

Alcohol
And, finally, as noted above, there is absolutely no store of alcohol in the body.  None whatsoever.  Effectively, alcohol is seen as a sort of metabolic ‘toxin’ or ‘poison’ to the body.  And this means that alcohol oxidation is 100% perfect, that is, the body will effectively do everything in its power to get rid of the alcohol increasing alcohol oxidation to maximum (which means decreasing the oxidation of other nutrients consumed with that alcohol) so that the alcohol can be gotten rid of.

I’m going to ask readers not to read anything into the above paragraph, don’t infer or try to draw conclusions about how alcohol might or mightn’t fit into the diet in terms of anything.  As it turns out, alcohol is an oddity among nutrients with seemingly contradictory effects on things.  I’m going to address that in detail in a forthcoming article and, for now, just take the above as some much needed background information.

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Summing Up

And that’s that.  After consumption and digestion, nutrients have a couple of primary fates in the body which are oxidation (burning) and storage (for use later).  And, as it turns out, the propensity for the body to store or oxidize a given nutrient is related to the body’s built-in store relative to intake.  In the case of dietary fat, where stored fat is much higher than daily intake, the body tends to store incoming fat and burn very little.  Fat intake per se has very little impact on fat oxidation rates.

Rather, the rate of fat oxidation is related to carbohydrate intake as the body is able to precisely alter carbohdyrate oxidation to changing intake.  Eat more carbs and burn more carbs (and less fat); eat less carbs and burn less carbs (and more fat).  Protein is somewhere in the middle, oxidation can increase or decrease relative to intake but the effect takes time (3-9 days).   Finally is alcohol, with no storehouse in the body, alcohol oxidation will take 100% precedence over everything else when it is consumed.   I’ll discuss the implications of this in an article on alcohol (and it’s rather schizoid effects on body weight and body composition in a later article).

Oligosaccharides

The term oligosaccharide is used to refer to any carbohydrate chain between 2-10 molecules long (‘oligo’ = ‘several’ or as I like to call it ‘a buncha’; ‘saccharide’ = sugar).  Chemically, that is, an oligosaccharide, is a buncha monosaccharides that are chemically bonded together but there are only 2-10 of them in the chain (this will make more sense when I discuss polysaccharides).

And while some of the longer chains may be found in small amounts in the diet or in specialty food products (e.g. some maltodextrins which are a combination of maltose and dextrose may be about this length) by and large the primary oligosaccharides are the disaccharides, two sugar molecules bound together.  I’ve listed the primary dietary disaccharides in the table below including what two sugars they are made up of along with where they are generally found in the diet.

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While I’m hesitant to mention high-fructose corn-syrup (HFCS) in this article, I’m going to bring it up since it is also a combination of glucose and fructose (like sucrose), as discussed in the article Straight Talk about High-Fructose Corn-Syrup: What it is and What it Aint.  I’d only ask that you take any comments about HFCS to that article instead of this one since most of what needs to be said is there and needn’t be repeated here.  Simply recognize that, nutritionally, HFCS and sucrose are essentially identical in that both are made up of roughly 1/2 glucose an 1/2 fructose; that’s all I’m going to say about it.

Sucrose is arguably what most think of when they think of ‘sugar’.  Table sugar is pure sucrose and sucrose has traditionally been used as a sweetener for, well, forever in various forms (including cane sugar, refined sucrose and many many others).   As a sweetener, sucrose is used in various candies, as a sweetener in some sodas and is also found occurring in many foods whether naturally occurring (even fruit contains some sucrose) or man-made.

Lactose, as mentioned is a mixture of 1/2 glucose and 1/2 galactose and is found in dairy products.  Many people are probably familiar with lactose due to issues of lactose intolerance.  Lactose intolerance occurs due to an inability to digest lactose in the stomach due to either the complete lack (or more usually an inadequate amount) of the enzyme lactase in the stomach.  Lactose intolerance typically develops shortly after weaning (if it happens at all) and is more common in ethnic groups who did not evolve consuming milk past that point.  As a very gross generalization, the darker someones skin, the more likely there is for lactose intolerance to be present.

The symptoms of lactose intolerance generally include gas, diarrhea and stomach upset; this is due to the undigested lactose hitting the colon where it ferments.  Individuals with lactose intolerance (not to be confused with a true milk allergy, see A Quick Look at Food Intolerances and Allergies) must either avoid dairy products, consume special lactose removed products (e.g. Lactaid milk) or consume lactase supplements with dairy products.  Lactose intolerance and how to deal with it (for example, some with more minor lactose intolerance can consume dairy with meals) is discussed in more detail in The Protein Book.

Maltose, as noted above, is used primarily to brew beer and make malt drinks, it is also produced during the digestion of the polysaccharides (discussed next).  As well, maltodextrins are often found/used in specialty food products.  But for the most part sucrose and lactose are the primary oligo/di -saccharides found in the ‘normal’ diet.  Even if we include HFCS as a disaccharide, it’s generally made for commercial products and doesn’t occur naturally in the diet (to my knowledge).

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Polysaccharides

And finally are the polysaccharides, a term that refers to chains of sugar molecules which can range from several hundred to many thousands long (‘poly’ = ‘many’).    In terms of the human diet, polysaccharides almost universally refers to starch which is simply a long, long (long) chain of glucose molecules strung together.  Even there there are slight distinctions with recent research finding differences between what are termed amylose and amylopectin, both of which are found in dietary starches.   The difference has to do with the molecular structure: amylose is simply a straight chain of glucose molecules while amylopectin has a branching structure.

Both types of carbohydrates are found in dietary starches although amylose is usually more prevalent.  Both high amylopectin and high amylose starches are available (e.g. waxy corn is 98% amylopectin) for specific food purposes.  Foods such as grains (refined or otherwise), potatoes, etc. are all food examples of starches that are eaten in various proportions in the human diet.

Polysaccharides actually start digestion in the mouth due to an enzyme called alpha-amylase. You can test this by putting a piece of bread or something in your mouth and chewing without swallowing; after some time you’ll get a very sweet taste in your mouth due to the breakdown of starch to free glucose.  The old ‘carbohydrate blocker supplements’ (usually derived from white kidney bean) were actually alpha-amylase blockers, they prevented digestion of carbohydrates in the mouth.  Unfortunately, they didn’t do anything for the next step in digestion which occurs mainly in the stomach.  There, the long chains of starch molecules are broken down into smaller and smaller chains (producing some maltose for example) until the free glucose is available for absorption.

Although this isn’t related to the diet specifically, in the body (specifically muscle and liver) long chains of starch are called glycogen.  Again, these are simply long chains of glucose that are bonded together (in the liver, fructose is converted to glucose before being stored as liver glycogen) for breakdown at some later date.  Some recent work even suggests that there may be small stores of glycogen in the brain or fat cells but the majority will be found in muscle and liver cells.  On average, the liver may hold about 50 grams of carbohydrates and the skeletal muscle of an average sized person about 300-400 grams.  These values can be doubled with carbohydrate loading.

A question that I have seen enough times to think it worth addressing is why meat doesn’t provide carbohydrate to the diet due to the presence of glycogen in muscle (animal meat is just muscle). And the major part of the answer is that, after death, the glycogen will be broken down as part of the process of the animal going into rigor.  If you ate it fresh off the kill, depending on whether or not the animal stored glycogen or not (not all animals do), there might very well be glycogen still present.  But I’m talking fresh off the kill, like Ted Nugent you just shot it in the head with an arrow and you dig in with a knife right then fresh off the kill.  If you don’t do that, the glycogen will be gone.

I should also mention another type of starch which is ‘resistant starch’, this is actually a type of starch that is resistant to digestion, hence the name.  That is, it passes through the stomach and intestines without digestion (and may have certain health or weight loss benefits because of it).  Resistant starch is found naturally in small amounts in some foods but most of the focus seems to be on developing commercial foods higher in resistant starch.

Finally, fiber would technically be discussed here as a polysaccharide but, as I mentioned in Primer on Dietary Carbohydrates – Part 1, I already detailed fiber in Fiber – It’s Nature’s Broom and would refer readers there for more detail so I won’t spend much more time on it here.  Just realize that the various fibers are long chains of, generally indigestible, carbohydrate molecules (I say ‘generally’ as some fibers are metabolized in the colon to short-chain fatty acids as discussed in the linked article).

Summary

And that’s that, a primer on dietary carbohydrates.  Carbohydrates refers to a general class of compounds containing Carbon, Hydrogen and Oxygen (hence CHO) including monosaccharides (simple sugars), oligosaccharides (chains of 2-10 molecules) and polysaccharides (long chains of molecules including fiber).  I’ve summarized the primary types of dietary carbohydrates in the chart below.

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What is a Carbohydrate?

The term carbohydrate is sort of an overall classification referring to a number of different organic compounds, which I’m going to detail below.   You may often see the abbreviation CHO (for Carbon, Hydrogen and Oxygen) to refer to carbohydrate.  Although fiber is a carbohydrate, I’m not going to discuss fiber in detail in this article; rather I’d refer you to Fiber – It’s Natures Broom for a detailed look.

As I have discussed in many articles on the site, the primary role of carbohydrate in the body is energetic, that is it is broken down in cells to provide energy through a variety of pathways.   At the same time, strictly speaking, carbohydrate is not an essential dietary component; that is, you can survive without eating it at all (an explanation of essential vs. inessential nutrients can be found in A Primer on Nutrition Part 1).  How many carbohydrates should be consumed in the human diet is a topic of endless debate and controversy, I’d refer readers to How Many Carbohydrates Do You Need? for a detailed look at the topic.

Now, another term that is sometimes used to describe carbohydrates is saccharides and, with that trivial note made, there are three primary classes of carbohydrates which I’m going to first list and then describe in more detail below in terms of what they are, what they do in the body and where they are found in the food supply.

1. Monosaccharides
2. Oligosaccharides
3. Polysaccharides

To keep the article length under control, I’m only going ot discuss the monosaccharides today.  I’ll discuss oligosaccharides and polysaccharides (along with an article summary on Tuesday of next week).

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Monosaccharides

The term monosaccharide refers to a single ‘sugar’ molecule (‘mono’ = single; saccharide = ‘sugar’) and are often referred to as simple sugars.  The monosaccharides are glucose (blood sugar), fructose (fruit sugar) and galactose (milk sugar).  I should mention that there are other monosaccharides but the above three are the ones primarily found in the diet.

One that does come up on fitness forums (due to its use in many sports products) is dextrose which is simply d-glucose.  The ‘d’ refers to the chemical structure (normal glucose would be more accurately described l-glucose and you can technically have both d- and l-fructose) and I’ll leave it to the organic chemistry nerds to worry about it beyond that. Simply recognize that both dextrose and glucose are a form of glucose (effectively they are molecular mirror images).

Now, free glucose is found in some foods (fruit has some and many types of candy will contain glucose) although it’s primarily associated with blood sugar (when diabetics are measuring their ‘blood sugar levels’ they are measuring blood glucose levels specifically). This is because glucose is the type of sugar found almost exclusively in the bloodstream of humans.  Quite in fact, almost all other dietary carbohydrates will either be converted to or simply appear in the bloodstream as free glucose.

This is certainly true of dietary fructose, found primarily in fruits (hence the name) which must first be converted to glucose (in the liver) prior to release.  That is, contrary to some claims being made, free fructose is almost never found in the bloodstream in large quantities unless it was put there through infusion.   Rather, dietary fructose will either be stored in the liver as glycogen (see below) before being converted to glucose and released into the bloodstream, or simply converted to glucose and released after consumption.  Again, free fructose is rarely found in the bloodstream in appreciable quantities even when it’s consumed in the diet.

I should probably mention that fructose got a lot of press one point as either a superior sweetener or a sugar that was ideal for diabetics.  In terms of the latter, due to it’s slow digestion and general lack of effect on blood sugar or insulin response, dietary fructose was thought to be superior to sucrose.  However, it’s turning out to be much more complicated than that.  Excess dietary fructose (and please note my use of the word ‘excess’) can cause problems in terms of raising blood triglycerides and having other negative effects.

So, while the fear and scare-mongering of the anti-fructose brigade (who are often looking at insanely non-physiological amounts of fructose; amounts that simply aren’t achievable in a normal human diet) tends to be a lot of nonsense, there’s little doubt that too much fructose can be a bad thing.  I’d note, and this is discussed in some detail in the article (and especially comments section) of Straight Talk about High-Fructose Corn-Syrup: What it is and What it Aint that the fructose mainly becomes and issue when it’s being mainlined as part of sugary sodas.

It would take an absurd amount of say, fruit, to provide enough fructose to the diet to cause problems.  The liver can generally handle approximately 50 grams of fructose or so before you start to see conversion to triglycerides or other negatives (when you divide the studies up into those that find problems versus those that don’t, 50 g/day is about where the cutoff occurs).  While that intake level might be easily achievable by someone consuming a lot of sugary soda, given taht an average piece of fruit is roughly 7% fructose (e.g. 7 grams fructose per 100 grams of fruit), well..that’s a lot of fruit (~7 average pieces per day).  But, in my opinion, anyone consuming gallons of sugary soda per day has bigger issues in their diet than the HFCS/fructose intake.  But I digress.

Finally is galactose, or milk sugar, found, as you might imagine in milk and dairy products.  I don’t have much to say about this one here but will come back to it below.  I’d only note that galactose tends to be metabolized similarly to fructose in the body; that is it’s dealt with in the liver. Since galactose tends to make up a fairly small amount of the overall diet (unless massive amounts of dairy are being consumed), I don’t usually consider this worth worrying about.

As a final note, there are a host of other types of monosaccharides that can either occur in small amounts in the diet or be made.  Ribose is one simple sugar, for example, that was one promoted to improve performance.  Some of the sugar alcohols (e.g. xylitol) also fall into the category of monosaccharide but since they are modified carbohydates (simple sugars with an alcohol molecule tacked on), I’m not going to discuss them here.

Simply while there are far more monosaccharides that can be found in the diet (or at least obtained), glucose and fructose are going to be the major players (and glucose more than fructose); galactose intake will depend entirely on dairy intake or the lack thereof.

And that’s where I’m going to wrap it up for today.  On Tuesday of next week, I’ll discuss oligo- and poly-saccharides and sum up the topic overall.

Read a Primer on Dietary Carbohydrates – Part 2.

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.Fat and Cholesterol

Although I recently examined Fat and Cholesterol in some detail in A Primer on Dietary Fats Part 1 and A Primer on Dietary Fats Part 2 back in May, I want to take a briefer, more streamlined look at them in today’s article.  Readers wanting more details can click the above links.

Even though they are chemically and nutritionally distinct substances, dietary fat and cholesterol are so linked in the minds of most people that I’m going to discuss them together.   As well, along with the never-ending debate over carbohydrates in the diet, the issue of dietary fats is one of almost constant debate in both nutritional sciences and among nutritional experts.   I’m not going to get into those debates in any real detail here (since it’s about the basics) but interested readers can read Carbohydrate and Fat Controversies Part 1 and Carbohydrate and Fat Controversies Part 2 if they want more details.

First let met get cholesterol out of the way since I don’t actually have a tremendous amount to say about it. Cholesterol plays a number of roles in the body not the least of which is involvement in the structure of cell membranes in the body.  As well, cholesterol provides the ‘base’ for the steroid hormones, testosterone, estrogen, progesterone and others are synthesized out of cholesterol in the body.

Of course, when most people hear the word ‘cholesterol’, they immediately think heart disease and, certainly, one aspect of cholesterol metabolism in the body is that it can cause atherosclerotic plaques (essentially the cholesterol builds up in arteries, potentially blocking blood flow).

Please note: I am vastly simplifying a much more complicated topic.

And this tends to be the source of much confusion, especially among the lay public, about diet; they confuse dietary cholesterol intake with blood cholesterol (aka blood lipid) levels.  I’d note, and again this is more complicated than I want to cover here, that blood cholesterol levels are only one of several contributors to the issue of heart disease.  Others contribute.

But there tends to be an idea that dietary cholesterol intake is a primary determinant of blood cholesterol levels when, simply, this isn’t generally the case.  Certainly a percentage of people seem to be sensitive to dietary cholesterol intake (in terms of how their blood cholesterol responds) but, in the majority, dietary cholesterol intake per se has very little impact on blood lipid levels.

As well, your body generally makes more cholesterol (in the liver) than you eat in a day; that’s unless dietary cholesterol intake is exceedingly high.   Additionally, the live modifies how much cholesterol it produces depending on daily intake.  If dietary cholesterol intake goes up, the liver makes less; if dietary cholesterol intake goes down, the liver makes more.  The body is smart that way.

Rather, the types and amounts of dietary fat being consumed play a far larger role in blood lipid levels.  Frankly, I don’t have much more to say about dietary cholesterol, it’s simply not that big of a deal unless you are in that small percentage of folks who are sensitive to it.  Rather, I want to talk a bit more about dietary fats.

Of course, a primary role of dietary fats in the body is to be used for energy and it was assumed for many years that this was the only real role of fat, to provide energy storage.  This was especially true of stored body fat which was thought for decades to provide only a passive storage depot of energy; rather it turns out that fat cells do much more in the body, producing hormones and such that affect myriad processes elsewhere in the body (a topic I’ve discussed at length on the site and in my books)..

Fats are also found in the cell membranes of various tissues (and the type of fat stored there can affect various cellular processes).  As well, fats can be used to make eicosanoids, chemical messengers made from specific fatty acids that affect numerous biological processes.  Specific dietary fats can also affect gene expression in certain cells, impacting on things like fat storage and oxidation and many others.

From an energetic standpoint, fats are typically assigned a caloric value of 9 kilocalories/gram (~38 kj/g); there are slight differences between specific fatty acids however.  As well, there is some evidence that different fats have a slightly different propensity to be stored vs. burned after consumption although the differences between the fatty acids are relatively small.  I’d mention for completeness that dietary cholesterol has no energetic value to the body.

The biggest controversies regarding dietary fat usually revolve around the health effects of its consumption. It’s not unfair to say that, for many years now, dietary fat has been the whipping boy of the nutritional world (though carbohydrates are taking that role in recent years): fat makes you fat, fat causes heart disease and cancer, fat is probably responsible for terrorism in the US and the decline in the family unit. You name it and the problem has probably been blamed on dietary fat by certain groups.  At the other extreme are folks who argue that dietary fats have no health negatives, that they can be consumed effectively without limit or concern.

As with so many extremist stances, the truth is a little different and tends to lie somewhere in the middle.

In the past ten years or so, the issue of fat quality (i.e. type of fat) has become just as important as that of fat quantity (i.e. amount of fat). Simply put: all fats are not the same in terms of their effects on health.  As well, whether a specific fat is good, bad or neutral in terms of health depends to a great degree on the context in which it’s eaten; this is a concept that neither extremist group can seem to wrap their heads around.

Whether the person is active or inactive, fat or lean, the rest of their diet, gaining or losing weight, and a host of others all contribute to the effect a given fat will have on the body.  I’m not going to go into further details here, I’d suggest you read Carbohydrate and Fat Controversies Part 1 and Carbohydrate and Fat Controversies Part 2 for more details.

In any case, dietary fats are generally divided into four distinct categories, I’m going to look at each in brief next.

Trans-Fats

Trans-fatty acids are a man-made fat made by bubbling hydrogen through vegetable oil to make it semisolid with a longer shelf-life; I’d note that there are naturally occurring trans-fatty acids found in foods as well.  Margarine is probably the example most readers are familiar with although trans-fatty acids (also called partially hydrogenated vegetable oils) are commonly found in most processed foods (there is currently a big push for trans-fat free foods to be produced commercially).

Of the four types of fats, trans-fatty acids have the least amount of debate around them; their intake at even low levels tends to have exceedingly detrimental impacts on things like blood lipid levels and diabetes risk.  Due to the high reliance on processed foods in the modern diet, trans-fatty acid intake is thought to be at least one part of the problems being seen in the modern world (note: there are certainly other contributors).

Saturated Fats

Saturated fats are found almost exclusively in animal products (two exceptions are coconut and palm kernel oil) and are solid at room temperature.  Traditionally, the impact of saturated fats on blood lipid levels and heart disease risk has been thought to be universally negative but it turns out to be much more complicated than this.  While some saturated fats do reliably raise blood cholesterol levels (primarily due to an impact on liver metabolism), others are completely neutral.   Anybody interested in this topic may wish to read the journal article Saturated Fats: What Dietary Intake.

As well, as I mentioned above there is far more to heart disease risk than just blood cholesterol levels.  And, as also noted above, the overall impact of any fat (including saturated fats) on health risk depends on the context of their intake.  In one context (e.g. low fruit/vegetable/anti-oxidant intake, high stress, inactivity, high body fat, excessive total energy intake), a high saturated fat intake may be exceedigly harmful.  In a different context (e.g. high fruit/vegetable intake, low stress, high activity, low body fat, appropriate energy intake), they may have no effect.  I hope that any of the pro-saturated fat folks reading this article will read this paragraph a couple of times before they leave me comments about how I’m anti-saturated fats.

I’d finish by noting that saturated fats are not an essential nutrient.  They aren’t required for life and, even if they were, the body can produce them from other sources.

Monounsaturated Fats

Monounsaturates are present in almost all foods which contain fat and are liquid at room temperature (quite in fact, the majority of fat in most ‘high-fat’ foods is monounsaturated).  Olive oil is arguably the most well-known of the monounsaturated fats and has received a great deal of attention as a relatively healthy fat. Monounsaturates have a neutral, if not beneficial, effect on health and it’s thought that the high olive oil consumption among Mediterraneans is partly responsible for their robust health (there are ceertainly other factors involved here).

Like saturated fats, monounsaturated fats are not an essential nutrients, they may confer health benefits but they are not required for survival.

Polyunsaturated Fats

Polyunsaturated fats are found primarily in vegetable oils and are liquid at room temperature. They are generally claimed to have a positive effect on human health although, as always, things are a little more complicated than that.  Polyunsaturated fats come in two major “flavors”, referred to generally as omega-three and omega-6 fatty acids.

The omega-3 fatty acids include a number of different fatty acids including the ‘parent’ fatty acid alpha-linoleic acid (ALA) found in things such as flax oil along with the fish oils (EPA and DHA).  I would be surprised if anybody reading this hadn’t heard of the fish oils or their benefits.  In sum, fish oils do just about everything, they decrease inflammation, help with depression (especially while dieting), decrease enzymes involved in fat storage and increase the levels of enzymes involved in fat burning.   I’d finish by noting that the conversion of ALA to EPA is fairly low and the further conversion of EPA to DHA is basically insignificant.  For this reason, taking preformed fish oils is generally required to impact body levels of EPA/DHA to any great degree.

Similarly, the omega-6 fatty acids include a host of different fatty acids including linolenic acid (LA), found in many vegeteable oils, along with things such as arichnidonic acid (AA) which are made from metabolism or LA within the body.

I’d note that both the w-3 and w-6 fatty acids are part of a more general class of fats called essential fatty acids, that is they are essential nutrients; that is, as explained in A Primer on Nutrition Part 1, they are required for life and cannot be made within the body.  In the modern diet, it’s generally pretty easy to get w-6 fatty acids through the diet, unless folks consume fatty fish, w-3 are much harder to come by (hence the general need for some type of supplementation).

Now, there is some controversy over w-3 and w-6 intake with excessive w-6 intake being thought to cause some health problems (such as inflammation).  In the modern diet, the intake of w-6 fatty acids to w-3 is about 20-25:1 or so and it’s been thought that a ratio closer to 1:1 or 4:1 would be healthier with the excessive w-6 intake causes problems.  Some groups have even blamed current health problems less on saturated fat intake and more on a high w-6 intake due to the use of vegetable oils in the modern diet.

However, as I discussed in more detail in A Primer on Dietary Fats Part 2, current research calls this into question with mortality rate generally decreasing with increasing w-6 intake and some research suggesting no real impact on inflammation of ‘excessive’ w-6 intake.  I’m not going to go into any real detail here, please read that article for more information.

Dietary Fats: Summing Up

I expect the issue of dietary fats to remain an area of controversy for some time to come.  New functions of dietary fats are still being found and the impact of dietary fats on overall health (not simply limited to heart disease) will continue to be examined.  As I noted above, I feel that the impact of a given type of dietary fat on health is entirely context dependent, an issue that the individuals involved in both sides of the debate seem to have missed.  Since I’ve discussed this in detail in other articles linked in this piece along with touching on it briefly above, I won’t discuss it further.

Everything else: Fiber, Alcohol, Vitamins and Minerals

I recently looked in some detail at fiber in Fiber – It’s Nature’s Broom and only want to touch on it in brief here.  While not an essential nutrient (e.g. you won’t die if you don’t eat it), fiber does play a number of important roles in human health in nutrition.  If nothing else, high-fiber intakes tend to keep people full and, generally, high-fiber diets are associated with greater weight loss or at least less weight gain.  There are other effects as well, see the above article for the details.

Fiber can be subdivided into a variety of different categories but, practically speaking, the main ones of importance are soluble and insoluble fiber. Soluble fibers mix in water and take up a lot of space in the stomach, it also holds food in the stomach longer: this tends to increase feelings of fullness.  In contrast insoluble fibers don’t mix with water but help with bowel regularity and keep the colon healthy.

Both types of fiber appear to be important to human health and both are found in varying degrees in foods such as fruits and vegetables (grains have varying amounts of fiber depending on how processed they are).

Alcohol isn’t really a nutrient in that it provides nothing of actual nutritional value except for calories.  Even there, alcohol intake doesn’t seem to scale with predicted weight gain although nobody is quite sure why this is the case.  Some studies suggest that some alcohol calories go ‘missing’ but nobody can figure out where they are.  Alcohol also tends to impact on metabolism in a way that can promote fat gain.  Certainly alcohol can have a place in any diet (with a large body of research suggesting that moderate alcohol intake has health benefits depending on the specifics) but excessive amounts can cause varying problems.

Finally there are vitamins and minerals which serve innumerable roles in the body and which include a host of essential nutrients (again, can’t be made in the body, required for life).  Minerals such as calcium are structural (e.g. bone) along with being involved in cellular signalling.  Iron is involved, of course, in the formation of red blood cells, important for overall health and performance.  Zinc is involved in immune system function and a host of other processes (including appetite regulation).  Vitamins act as nutritional co-factors and are necessary for the body to function optimally.

Vitamins and minerals are found to some degree in all foods with amounts and types depending on the specific food.  Fruits and vegetables tend to be nutritional powerhouses in this regards but some vitamins and minerals are optimally consumed in foods of animal origin (for example, the iron in red meat is absorbed roughly ten times better than the iron in vegetable source foods and B12 can only be found ‘naturally’ in animal source foods).

In that context, I’d note that a class of nutrients called phytochemicals are only found in plant foods and there is currently a great deal of interest in the health benefits of these compounds.  They aren’t essential by any stretch but may confer health benefits.   Various anti-oxidant nutrients are also found in varying amounts in these foods and, while anti-oxidant supplementation has generally shown little to no real health benefits, diets high in food-based anti-oxidants have been found to confer many health benefits.

To keep the piece manageable, I’m going to divide it into two parts with Part 2 being run on Thursday.  Today I want to look at the issue of essential vs. non-essential nutrients as well as protein and carbohydrates.  On Thursday, I’ll tackle the issue of dietary fats along with everything else (fiber, alcohol, vitamins and minerals).

Essential vs. Non-essential Nutrients

The body has a requirement for somewhere around 60 nutrients on a daily basis for normal functioning.  Please note: as nutritional science has progressed, it’s now become apparent that many, many more nutrients may contribute to optimal health, although they are not necessarily required for survival.  Put differently, you can live without consuming them but you might be healthier or perform better if you did eat them.

I should also mention that this list of 60 nutrients includes things such as air and water that, while they aren’t considered as nutrients per se, are usually not an issue.  Put differently, if you’re having issues obtaining adequate amounts of air or water, you have bigger problems to deal with.

Of more relevance to today’s article, nutritional science often groups nutrients into the categories of essential and nonessential (recently the terms indispensable and dispensable have come into vogue) which is what I’d like to discuss next. For quick summary, there are roughly 8 essential amino acids, 2 essential fatty acids, a host of vitamins and minerals and a few others substances that are required on a daily basis.  You might note that carbohydrates were not listed as an essential nutrient, a topic I’ll come back to below.

So what is an essential nutrient as opposed to a non-essential nutrient?  I’m actually going to answer that by explaining what a non-essential nutrient is first.  Contrary to what it sounds like, the term non-essential (or dispensable) doesn’t mean that the nutrient isn’t essential for life; rather, it’s not essential that the nutrient be obtained from the diet itself.

Translating that into English, there are some nutrients (such as glucose, certain fatty acids and just over half of the amino acids) that can be made in the body from other sources.  For example, many amino acids can be made in the body via metabolism from other amino acids; as well, glucose can be made in the body from a number of different substances.    So while these nutrients are essential for life and survival, it is not essential that they be obtained from the diet.

At the same time, there are nutrients that cannot be made by the body (the vitamins and minerals are examples, so are the essential fatty acids and roughly the other half of the amino acids) and are hence considered essential nutrients. That is, it is essential that they be obtained from the diet (generally on a daily basis).

In short, to be considered essential, a nutrient must meet two primary criteria:

1. That nutrient is required for survival
2. That nutrient cannot be made in sufficient quantities (or at all) by the body

So if a nutrient isn’t required to keep you alive, it’s not essential (even if consuming it improves health or what have you).  If it’s required for life but the body can make sufficient amounts of it, it’s still not essential to get it from the diet; hence it is not an essential nutrient.  Only when a given nutrient is both required for survival and can’t be made in the body in sufficient amounts is it an essential nutrient in terms of what I’m talking about here.

Although I want to keep this piece focused on the basics, I should probably mention one odd exception which is Vitamin D (currently getting a lot of press, and for good reason, in various places).  Vitamins and minerals, generally, can’t be made in the body and must come from the diet.  But while Vitamin D can be obtained from the diet (many foods are fortified with it), and is an essential nutrient, it is actually made by the body in response to sunlight hitting the skin.

I want to make it clear that the above is a bit of a simplification and the topic of essential and non-essential nutrients can be made considerably more complicated.  For example, some nutrients can be considered conditionally essential.  That is, under normal conditions, the body may make plenty of a given nutrient (meaning that it is not required that the nutrient come from the diet) but under other conditions the body needs more than it can make.   Under those conditions (usually involving things like disease and severe trauma), a nutrient that is normally non-essential becomes essential (must be obtained from the diet).  Hence conditionally essential.

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Protein

The word protein come from a Greek word meaning “the first” which is meant to signify its primary role in human nutrition.  While you can survive rather extended periods without carbohydrate or fats in the diet, a long-term lack of protein intake leads to a loss of body tissue (muscle and organ protein), function and eventually death.

Whole dietary proteins are made up of smaller units called amino acids of which ~20 occur in the diet (there are many more that occur in the body).  Of those 20 or so amino acids, roughly eight are considered essential meaning that they must come from the diet on a daily basis.  Under certain conditions, such as stress and trauma, some amino acids also become conditionally essential; glutamine is perhaps the most commonly cited example with much higher amounts that can be made in the body being required under those kinds of conditions.  There are other examples but few would be relevant outside of some very very specific situations (usually involving severe malnutrition or disease).

A primary distinction between protein and carbohydrate/fat is that only protein contains dietary nitrogen (which is technically an essential nutrient).  Since humans can’t ‘fix’ nitrogen from the air like plants, we have to obtain it from the diet.  And that nitrogen is found in the individual amino acids that make up whole food proteins.   Also, while there can be some interconversion of protein (more accurately, amino acids) to carbs or fat (this last one is very rare), neither carbs nor fat can be made into amino acids.

Proteins/amino acids have a number of crucial roles in the human body but most of them are structural (meaning the protein is used to build things).  Many hormones are made of protein (some examples are IGF-1 and Growth Hormone), your organs, muscles, skin and hair all contain protein; protein has numerous other roles in the body as well.  Protein can also be used to produce energy in the body, usually by conversion to other nutrients (almost always glucose).  For example, during long-term aerobic exercise, the breakdown of amino acids (specifically leucine) can provide 5-10% of the total energy generated.

Something to note is that, in contrast to carbohydrate (which is stored in both muscle and liver) and fat (which is stored on your butt and stomach), there is no real storage form of protein unless you count the relatively small amount floating around in the bloodstream and the protein that makes up your muscles and organs.  But this isn’t a true storage form like for carbohydrates and fats since, in general, breaking down body protein is a bad thing (as I mentioned above).

In the diet, protein is found to some degree in almost all foods with the exception of pure fats like vegetable oils and such and some totally refined carbohydrates such as candy (e.g. jelly beans). Fruits and vegetables contain fairly small amounts of protein (perhaps a gram or two per serving) while beans and nuts can contain significant amounts of protein. But most people in modern society get their protein from animal based products: meat (red meat,  chicken, fish), milk, cheeses, etc.

In terms of caloric content, protein has traditionally been assigned a value of 4 kilocalories/gram (~16.8 kj/g) but this is currently a topic of some debate.  Because of how it is digested and assimilated in the body, at least one researcher is suggesting strongly that protein be given a lower caloric value (roughly 3.2 kcal/g or 13 kj/g) than the traditional value.

I covered a great deal of detail regarding different dietary proteins on the site in What’s Are Good Sources of Protein; of course The Protein Book also discusses this topic in detail.

Carbohydrate

The term carbohydrate refers to a number of different organic compounds ranging from simple sugars (e.g. glucose and fructose) to disaccharides (e.g. sucrose, lactose) all the way up to starches (long chains of individual carbohydrate molecules bound together).   Because of it’s chemical structure, you will often see carbohydrate abbreviated as CHO (for carbon, hydrogen, oxygen).

In the body, carbohydrate’s role is primarily energetic, that is it provides energy (through breakdown) in various tissues of the body.  Most tissues in the body can use glucose for fuel and, quite in fact, most will use glucose if it is available (they will switch to using fats or ketones if glucose is not available in sufficient amounts).  A few tissues of the body can only use glucose for fuel.

And while the above might suggest that dietary carbohydrates are essential, this isn’t the case.  Recall from the discussion above that, to be considered essential a nutrient must not only be required by the body but cannot be made in sufficient quantities.  And, as I’ve also discussed elsewhere, the body is able to produce some carbohydrate from the breakdown of other nutrients, specifically about half of the amino acids, glycerol (the backbone of both dietary and body fat) and lactate.

In general this process (called gluconeogenesis which simply means the production of new glucose)  is able to cover the body’s basic daily needs.  As well, with low-carbohydrate diets, there is a whole body shift in fuel use from carbs to fats and ketones which reduces carbohydrate requirements.  This is discussed to some degree in nearly all of my books but the greatest detail can be found in The Ketogenic Diet.

I would finish by noting that high-intensity exercise tends to increase carbohydrate requirements beyond what the body can make putting carbohydrates into the conditionally essential category I discussed above (e.g. the body needs more than it can produce itself).  For those individuals who wish to perform high-intensity activity such as intensive weight training or even high intensity metabolic work, some amount of carbohydrates generally becomes required in the diet.  The issue of daily carbohdyrate requirements is discussed in much more detail in How Many Carbohydrates Do You Need?

Carbohydrates can be stored within the body in the liver or muscle as glycogen (a long chain of glucose molecules bonded to each other) and is found in small amounts (~5-10 grams total) as free glucose in the bloodstream.  Liver glycogen exists primarily to help maintain blood glucose levels while glycogen within skeletal muscle can only be used by the muscle that it’s stored in; it can’t be released back into the bloodstream.

Dietarily, traditionally carbohydrates have been divided somewhat simply into two major categories (this is especially true in athletic subcultures but is often used generally) which are fibrous and starchy.  Please note that this is mainly a division of convenience but it tends to be useful practically so I’ll stick with it.

Fibrous carbohydrates generally refers to vegetables which, with a few exceptions, tend to contain very small amounts of digestible carbohydrate while containing a lot of fiber.  Pretty much any vegetable you care to name (with the handful of exceptions mentioned next) will fall into this category of carbohydrates and it’s often stated that you can eat these types of carbohyrates ‘without limit’ due to their generally low caloric content.  I’ll come back to this shortly.

Starchy carbohydrates are, more or less, everything else: breads, pasta, rice, and grains, basically any carbohydrate that contains a good bit of digestible carbohydrate. I should note that there are a few starchy vegetables such as carrots, peas, corn and potatoes: vegetables which contain larger amount of digestible carbohydrate and which need to be counted as starches in terms of real-world meal planning.  Fruits, while not technically a starch, are usually grouped with starches since they contain quite a bit of digestible carbohydrate (the majority of which are simple sugars).

Explaining the caloric value of carbohydrates can be somewhat confusing. Starchy carbohydrates are generally assigned an average value of 4 calories per gram (16 kj/g) although this can vary slightly from food to food.   Fiber is where it gets more confusing; as I recently discussed in Fiber – It’s Nature’s Broom, some types of fiber can be broken down to other things in the intestine and, recently, fiber has been given a caloric value of 1.5-2 kcal/g (~6.3-8.4 kj/g).  While this isn’t a large amount given most people’s average fiber intake, for people who are eating enormous amounts of vegetables (which don’t just contain fiber, mind you), the calories can start to add up.

And with those topics covered, I’ll stop here for today.  On Thursday, I’ll take another quick look at dietary fats along with the ‘everything else’ category of human nutrition: alcohol, vitamins, minerals and fiber (again).

Thankfully, soon thereafter leptin was discovered and nutritional researchers could start looking at things more interesting than why eating high-fiber vegetables were good for you (a nutritional tidbit that I file under the ‘Grandma was right’ category).

Even so, there is still some confusion regarding fiber out in the world of nutrition regarding fiber.  And boring or not, it’s a topic worth clearing up.  So today I want to take a fairly comprehensive look at dietary fiber, what it is, what it does in the body, how it impacts on things like body composition (and health to a lesser degree) and finish by looking at some (admittedly vague recommendations).

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What is Fiber?

Generally speaking, fiber is included within the category of dietary carbohydrates (many athletes or bodybuilders divide carbohydrates into starchy and fibrous for example).  But fiber is distinct enough to be considered separately from other types of digestible carbohydrates.  Perhaps surprisingly, defining what is and isn’t a fiber is actually a more complicated issue than most would think.

Chemistry, botanical and physiology types all sort of want to use different definitions and spend altogether too much time arguing about what is and what isn’t a fiber.  Since I’m less interested in chemical or botanical issue than physiological ones, I won’t bore people with the details of those of those definitions and arguments.  Rather, I’m interested in the physiological effects and, hence, the physiological definitions.

Even there there are two primary definitions which are used:

1. Soluble vs. insoluble (aka viscous vs. non-viscous)
2. Fermentable vs. infermentable

I suspect that most are at least passingly familiar with the first definition above.  If not, here’s what it means.  Soluble fibers go into solution in liquid.  A good example is guar gum, if you put a spoonful in water and mix it, it will turn into this gel-like mass; that’s because it’s soluble in fluid.  Insoluble fibers, in contrast don’t do this, you can mix them until the cows come home but they won’t ever go into solution.

I suspect that readers are relatively less familiar with the fermentable vs. infermentable definitions.  I’ll come back to this below when I talk about the caloric value of fiber but, simply, some fibers can be fermented (specifically by bacteria in the intestine) into other things (e.g. short-chain fatty acids, CO2 or methane) while others are infermentable (they cannot be converted into those other things).

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What Does Fiber Do?

Fiber has a number of different effects in the body which are relevant to both health and body composition.  It’s worth noting that, strictly speaking, fiber is not an essential nutrient.  That is, you won’t die if you don’t eat it regularly (or at all) and there are cultures such as the Alaskan Inuit and the African Masai that subsist on a diet that is essentially devoid of fiber.  However, that doesn’t mean that a sufficient intake of dietary fiber isn’t good for you or can’t provide either health or body composition benefits.

Below, I’ve listed a bunch of the major effects of dietary fibers (and note that some of these occur in the upper GI tract, others in the lower but I’m not getting into that much detail) in terms of their physiological effects.

1. Promoting fullness/satiety
2. Slowing gastric emptying
3. Decreasing nutrient absorption
4. Improved glycemic control, secondary to delayed gastric emptying and impaired nutrient absorption
5. Decreasing blood cholesterol
6. Decreasing mineral absorption
7. Effects on insulin sensitivity via fermentation to short-chain fatty acids
8. A number of effects relevant to colon cancer
9. Helps with poopin’

I want to touch on each below although I’m going to focus more on some than others.

Satiety

One of the myriad signals for fullness during or after a meal has to do with the physical stretching of the stomach.  And high-bulk foods are far more likely to do this than low-bulk foods.  In this context, meals or foods high in fiber generally contain a lot of bulk in few calories (a topic I discussed in more detail in Energy Density).

Thus they tend to make people feel fuller both in the short- and long-term.  In this context, I recall a rather ‘brilliant’ study a few years back which found that people who ate salad first in a meal ate less total calories; the high-bulk, high-fiber items filled them up so that they ate less of the more calorie dense foods.   Another one for the ‘Grandma knew best’ file.

In a slightly different context, it’s worth noting that individuals who have trouble meeting their energy requirements (e.g. athletes or ‘hardgainers’) may find it better to save salads for the end of the meal specifically so that they don’t get full too soon before eating the higher calorie part of the meal.

Slowing Gastric Emptying

As I mentioned above, soluble fibers tend to form a gel-like substance in liquids and one consequence of a high soluble fiber intake is that gastric emptying (the rate at which foods empty the stomach) is slowed when they are eaten.  Basically, they cause the chyme (the partially digested nutrients in the gut) to form this big gel which empties the stomach more slowly.  This, along with the physical stretching of the stomach tends to keep people fuller in the longer term because the food stays in the gut longer.

Impaired Nutrient Absorption

Another effect, again primarily seen with soluble fibers, is an impairment of nutrient absorption, and this holds for carbohydrates, fats and dietary protein.  Essentially, due to the gel-like mass that is formed, digestive enzymes can’t get access to the other nutrients so that more is carried out of the body.  This means that high-fiber diets will result in less total caloric absorption, basically the left-hand side of the equation discussed in The Energy Balance Equation will be lower when a large amount of soluble fiber is consumed.

I’d note that the effect isn’t massive, fiber may reduce total fat absorption by about 3%, protein by 5%.  I can’t find a good value for carbohydrates at the moment.   Put more concretely, an increase in dietary fiber from 18 to 36 grams per day might reduce total caloric absorption by 100 calories per day.

Now, depending on how you want to look at this, it can be seen as either a good or bad thing.  For individuals trying to lose weight, higher fiber diets will not only have positive effects on fullness and the rest but will result in less total calories being absorbed from the diet.  Again, the high-fiber nature will reduce the Energy In side of the equation (which only counts calories which are actually absorbed).

On the other hand, for athletes or bodybuilders, the impact of a high-fiber intake could be seen as detrimental, especially given that soluble fibers impact on protein absorption.   While it would be nice if fiber only impacted on carb or fat absorption, that simply isn’t the case. As well, for athletes with very high energy demands, losing digestible energy due to a high fiber intake might not be the best thing.  Again, I’d note that the total impact isn’t massive but it is worth considering.

Improved Glycemic Control

One of the most well-known and talked about effects of a high-fiber intake is improvement in blood glucose control. Between the slowing of gastric emptying and impairment of carbohydrate digestion, high soluble fiber intakes tend to improve blood sugar control; rather then seeing larger spikes (due to rapid digestion) which can be followed by crashes, blood sugar levels are balanced out.  In that crashing blood glucose can be another stimulus for hunger, this can have an additional impact on hunger control between meals (especially important when dieting).

Decreasing Blood Cholesterol

I’m actually not going to talk about the impact of fiber intake on blood cholesterol levels in great detail.  Sufficed to say that high-fiber intakes tend to improve blood lipid levels and do this through a variety of different and inter-related mechanisms.  If you want more detail than that, pick up a nutrition textbook.

Impairment of Mineral Absorption

In addition to global impacts on carbohydrate, protein and fat absorption, dietary fibers can also negatively affect mineral absorption especially calcium, magnesium, sodium and potassium.  I’d note that, in general, this isn’t really an issue for concern unless the intake of those nutrients is insufficient in the first place.

As well, when fiber intake is increased from foods (as opposed to dietary supplements), there is generally an increase in mineral intake in the first place which should help to offset any issues.  For example, the fiber intakes of our evolutionary diet is thought to be massive (some have estimated it at 100-150 grams per day) but nutrient deficiencies aren’t seen; this is most likely due to the fact that the fiber is coming from nutrient dense fruits and vegetables.

However, when people start adding horse-doses of fiber supplements to their diet, problems can start.  Older readers may remember the bran craze in the 80′s, when bran was found to lower cholesterol, people starting eating it in massive amounts.  But they were often doing it from purified sources rather than whole foods.  While this may have improved cholesterol levels, it ended up causing issues with mineral imbalances because the massive fiber intake was not accompanied by an increase in nutrient intake.

Effect on Insulin Sensitivity via Fermentation to Fatty Acids

As I mentioned above, another categorization of fiber is that of fermentable vs. non-fermentable, referring to whether a given fiber can be fermented (via the bacteria in the gut) to other things.  The other things that most are familiar with are hydrogen, carbon dioxide and methane; these are what cause the gassiness that can occur with high-fiber intakes.  Specifically, methane is what give farts their wonderful smell.

But fiber can also be fermented to short-chain fatty acids such as acetate, propionate and butyrate that are re-absorbed into the body and which have a variety of physiological effects.  One of those is to provide calories, a topic I’ll come back to shortly.  But the other is to impact on fuel metabolism.

The short-chain fatty acids provided by fiber fermentation impact on both fat cell metabolism and insulin sensitivity.  And while these short-chain fatty acids positively impact on insulin sensitivity, they appear to do it by blunting the release of fatty acids from the fat cell.   Yes, that says what you think it says: high-fiber intakes may be limiting fatty acid release from fat cells.  I’ll come back to this below.

A Number of Effects Relevant to Colon Cancer

Again, not a topic I’m going to get into much detail on.  Sufficed to say, high-fiber intakes have a number of physiological effects that reduce the risk of colon cancer.  Get a textbook for more.

Helps with Poopin’

And, of course, possibly the most well known effect a high-fiber intake is regularity and comfort in pooping.  That’s actually what the title of this piece refers to, I have often commented that fiber is nature’s broom.  It helps sweep stuff through the intestines and out the other end.  It does this through a number of mechanisms.

First and foremost, fiber speeds the transit time of food from one end of the intestines to the other.  So rather than sitting in the intestines, it moves towards the exit more quickly.  As well, fiber contributes to fecal bulk, essentially the size of the poo that is produced.  This increase in bulk also pulls more water into the fecal mass which makes the poop softer and easier to pass.  Both of these latter effects further contribute to the decreased transit time and all of this contributes to better regularity.

And, at the end of the day, who can argue with a good poop?

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Fiber and Energy Balance

Relevant to issues of body composition, fiber can contribute in a number of ways to The Energy Balance Equation.  As noted above, fiber impacts on caloric absorption (decreasing it, generally) along with fullness (which may cause people to spontaneously eat less) along with blood glucose control and several other mechanisms.  In general, the effect is to reduce either total food intake or caloric absorption, facilitating weight loss.

I’d mention again that the effect of fiber on fat cell metabolism via the conversion to short-chain fatty acids is perplexing, one way of looking at this is that high-fiber intakes might hurt with fat loss.  This might become more relevant when people get very lean and fatty acid mobilization is becoming more difficult (for reasons discussed in The Stubborn Fat Solution).  At the same time, real-world results call the real-world significance of this into question.  High-fiber intakes have been part of hardcore diets for decades and folks seem to be doing alright.

Depending on the goal (e.g. weight loss vs. weight gain), this can be seen as good or bad depending on the context.  For individuals trying to lose weight, most of the effects of a high-fiber diet could be seen as generally positive.  Being fuller with more stable blood sugar and absorbing fewer calories would seem a good thing.

As noted above, for individuals trying to increase their energy intake and/or gain weight, a high-fiber intake could potentially be a negative.  Between making the individual fuller at a given meal and/or keeping them fuller longer during the day, along with impairment of caloric absorption, high-fiber intakes might have a negative impact overall for some people.

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Newsflash: Fiber Provides Calories to Humans

But there is another effect of fiber on energy balance that often goes unappreciated.  Backing up, it’s often stated that fiber provides no calories to the body since humans lack the enzymes necessary to digest it.  This has often been taken even further to claim that high-fiber vegetables are ‘negative calorie foods’, that is they take more calories to digest than they provide (assumed to be zero).

Here’s the thing: it’s not true.  Not entirely anyhow.

Above I discussed the issue of fermentation of some types of fiber to short-chain fatty acids which are then reabsorbed by the body.  Well, those fatty acids provide calories to the body.  While there is still some debate in the area, researchers have assigned a caloric value to fiber of 1.5-2 cal/gram (depending on the specific type).

Admittedly this is an average and will depend on the specifics of the diet and the type of fiber but, simply, the idea that fiber provides no calories to the body is not true. While the caloric value of fiber is still lower than starchy carbohydrates (4 cal/g), it is not zero.

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How Much and What Kind of Fiber?

So how much fiber do we need?  As noted above, strictly speaking fiber is not an essential nutrient; you might be healthier with it but if you never ate another gram you would not die.  You might want to die when you tried to poop but you wouldn’t actually die without it.

But due to the non-essentiality of fiber for human survival, it’s hard to make specific recommendations for daily fiber intake.

The American Dietetic Association recommends an intake of 10-13 grams of fiber per 1000 calories consumed.  This is roughly 20-30 grams per day for an average day’s diet of 2000-3000 calories per day.  It’s worth noting that the average fiber intake in the modern diet is about 10-11 grams/day which is far below this. Most people would probably benefit from eating more fiber but they’d also generally benefit from eating more fruits and vegetables generally.

As I mentioned, our evolutionary diet is thought to have contained absolutely massive amounts of fiber on average, intakes of 100-150 grams/day has been thrown around in some scientific papers.  I would note again that this would have come from the intake of massive amounts of fruits and vegetables, providing numerous other nutrients (especially minerals and vitamins) that wouldn’t be found if you tried to get that much fiber from supplements.

In that context, it’s worth mentioning that high-fiber foods, typically fruits and vegetables, contain tons of other nutrients important to health or what have you so looking only at the fiber content can be a bit misleading.  Getting adequate amounts of high-fiber fruits and vegetables on a daily basis has benefits far beyond just the fiber content; getting some at each meal would seem to be a good thing.

And yes, I am waffling on this.  There is very little hard and fast data on optimal fiber intakes for any goal.  Too little is bad, too much is probably bad.  Somewhere between those two extremes is about right.    People eating the modern diet get too little fiber and should increase it.  I’ve seen some meal plans that, frankly, included absurd amounts of fiber (folks with eating disorders often do this type of thing to stave off the gnawing hunger).  Find balance, people.

Depending on meal frequency, somewhere between 5-10 grams of fiber per meal would seem a decent place to start.  That should provide anywhere from 30-60 grams of fiber per day, covering average recommendations without being excessive.

I would note that if you fiber intake is currently low, do NOT try to increase it drastically in a short period of time. The body needs time to adapt to big increases in any nutrient intake and people who jump their fiber intakes massively often pay a hard price in terms of gas and such.

Finally, on the topic of types of fibers, I don’t get overly concerned with it.  The soluble/insoluble fibers can be further subdivided into a whole host of other categories but I consider this nutritional minutiae of little real relevance.  If you strive to consume a variety of fruits and high-fiber vegetables on a day to day basis, you’ll get a mix of fibers and cover your bases.

In specific situations, fiber supplements may play a role (for example, soluble fibers such as guar gum can be put into yogurt/protein powder mixtures to thicken it up and/or help with fullness on a diet).  And many will use psyllium husks as a form of insoluble fiber if they are having issues with constipation or what have you.  But, for the most part, I’d rather see people increase their intakes of high-fiber whole foods rather than use purified supplements.