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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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.

This is a topic that I discussed in some detail in Carbohydrates and Fat Controversies Part 1 and Carbohydrate and Fat Controversies Part 2 and I’d recommend readers take a look at those for a slightly different look at the issue than what is discussed here.

Arguments over recommended carbohydrate intake have a long history and it doesn’t appear to be close to ending any time soon. Typical mainstream recommendations have carbohydrates contributing 50% or more of total calories while many low-carbohydrate advocates suggest far fewer (ranging from the 40% of the Zone diet to close to zero for ketogenic diets).

This article looks at the topic in detail. And while I originally wrote it quite a while back (some of you have probably seen it before), it was nice going over it with fine toothed comb for an update. While the majority of it stands up well over time, I was able to make some slight changes to the values, along with removing some original stuff that wasn’t really relevant. Enjoy.

Introduction

It’s safe to say that most carbohydrate recommendations that you will see are put in terms of percentages, you should be eating 45% of your calories as carbs, or 65% or whatever number is being used.

As I discussed in Diet Percentages: Part 2, I don’t like this method. Rather, putting nutrient recommendations in terms of grams per kilogram or per pound is generally more valid (with one exception I discuss below). The percentages are simply meaningless without knowing how many carbohydrates are being provided in terms of gram amounts.

In that context, a typical ketogenic/low-carbohydrate diet might contain 0.5 g/lb (~1 gram/kilogram) of carbohydrate. An average moderate carb diet (such as The Zone or Duchaine’s Isocaloric Diet) might contain 1 g/lb (~2 g/kg) of carbohydrate or slightly more.   A typical high-carbohydrate diet would, of course contain more than that (perhaps 2-3 g/lb or more).  Typical recommendations for endurance athletes are in the 3-4 g/lb (6-8 g/kg) range and carb-loading may require 5-8 g/lb (10-16 g/kg) of carbohydrate.

Still, whether you’re looking at carb recommendations in terms of percentages of g/lb (g/kg), there is still a huge discrepancy between different experts. Some recommend lots of carbs, some recommend medium amounts, some recommend almost none.

Who’s right? Well, I am. Because rather than giving some single carbohydrate recommendation (that can’t possibly take into account all possible situations), I look at the individual and their needs to decide how many carbohydrates should be consumed daily.

Which is what I’m going to look at in detail in this article. The punchline, of course is that I’ll end up concluding that how many carbohydrates someone needs (or should consume) daily depends on the same factors that affect other nutrient recommendations: goals, preferences, types and amounts of activity, and our old friend, genetic variation. By the end of the discussion, I’ll have set both minimum and maximum intake values depending on different conditions that might crop up. Let’s start with minimum amounts.

Are Carbohydrates Essential?

Despite oft-heard claims to the contrary, there is no actual physiological requirement for dietary carbohydrate. Even the RDA handbook acknowledges this, right before recommending that a prudent diet should contain a lot of carbohydrates.

To understand why carbs aren’t essential, I need to discuss the concept of an essential nutrient briefly. And, in brief, an essential nutrient is defined as:

1. Any nutrient that is required for survival.
2. Can’t be made by the body.

Quoting from my own Rapid Fat Loss Handbook:

The second criterion is the reason that dietary carbohydrate is not an essential nutrient: the body is able to make as much glucose as the brain and the few other tissues need on a day-to-day basis from other sources. I should mention that the body is not able to provide sufficient carbohydrate to fuel high intensity exercise such as sprinting or weight training and carbs might be considered essential for individuals who want to do that type of exercise. I’ll come back to exercise later in this article.

But from the standpoint of survival, the minimum amount of carbohydrates that are required in a diet is zero grams per day. The body can make what little it needs from other sources. What, you ask, are those other sources? Read on.

Where Does the Glucose that the Body Makes Come from?

When carbohydrates are restricted completely, the body still has a small requirement for glucose (although this decreases over time) and the body has to find something to make glucose out of. That something is lactate and pyruvate (produced from glucose metabolism), glycerol (from fat metabolism) and some amino acids. It’s the amino acid use that can be problematic since they have to come from somewhere.

Now, if no food is being consumed (e.g. total starvation), that somewhere is generally muscle tissue (the body will also break down liver proteins); the body will readily break down body protein to scavenge the amino acids it needs to produce glucose. In doing so, the muscle released alanine and glutamine (produced in the muscle from the breakdown of leucine and the branch chained amino acids, so you know) which can be converted to glucose in the liver. This process goes by the unwieldy name of gluconeogenesis which just means the production of new glucose.

Protein losses during total starvation are extremely high to start, gradually decreasing as the brain switches over to using ketones for fuel (this reduces the body’s glucose requirements which means less protein has to be broken down to make glucose). Even so, during complete starvation there is always some loss of body protein. Over long periods of time, this goes from harmful (because function is compromised from muscle loss) to downright fatal. Especially as folks get extremely lean and body protein breakdown increases.

In this context, an under-appreciated fact of liver and protein metabolism (but discussed in detail in The Protein Book) is that over half of all ingested amino acids are broken down in the liver in the first place. A good portion of those can be used to make glucose and this is especially true when carbohydrates are restricted.

Switching from starvation to dieting, this is fundamentally a big part of why protein requirements go up when folks are dieting, more of the ingested protein is being used in the liver to make glucose, meaning that more total protein has to be ingested to make sure there is sufficient amounts to support things like protein synthesis in skeletal muscle.

I don’t want to discuss this in detail here (since this article is about carbohydrates) but the topic is covered to some degree in nearly all of my books. My original Ketogenic Diet had a thorough examination of protein sparing on a diet and, of course The Protein Book discusses how protein requirements change during dieting in detail.

I’d also note that, as long as protein intake is sufficiently high (e.g. the diet is covering the increased breakdown of protein in the liver and elsewhere), the amount of carbohydrates which are truly required is still zero; this is the basis of my Rapid Fat Loss Handbook approach: eliminate all non-essential nutrients (including carbohydrates) and provide only those that are essential (in this case large amounts of high-quality protein and essential fatty acids) to generate the largest deficit and maximum fat loss per day.

But, let’s assume that you don’t just want to eat massive amounts of protein, how many carbohydrates are needed to limit (or prevent) protein loss on a diet?

How Many Carbs Do I Need to Spare Protein Loss?

Early research into the topic of starvation and low-carbohydrate dieting found that as few as 15 grams of carbohydrates per day can limit nitrogen loss in the body. And raising carbohydrate intake to 50 grams per day severely limits the need for the body to use amino acids for gluoconeogenesis (which is why I suggested setting daily carbs on the low-carb days of The Ultimate Diet 2.0 at 50 grams).

This occurs via at least two mechanisms:

1. The increased carb intake maintains blood glucose and insulin at a higher level (inhibiting cortisol release).
2. The carbohydrate provides glucose for the brain, limiting the need to break down body protein.

Basically, in the context of dieting, dieters can either jack up dietary protein to cover the increased carbohydrate requirements of dieting or simply eat slightly more carbohydrates to provide them directly. Both have the same end-result. 15-50 grams per day limits the body’s need to break down protein and will allow protein requirements to be set lower than a diet providing essentially zero carbohydrates per day.

But What About Ketosis?

Since I’m going to use the term in just a second, I need to define what it means. When fatty acid burning is ramped up to high levels (as when carbohydrates are restricted), the body starts producing ketone bodies in the liver. As noted above, many tissues in the body can use ketones for fuel, basically they are an alternative energy source to glucose when it’s not available. When ketones build up in the bloodstream beyond a certain point, a condition called ketosis is said to develop. In contrast to the diabetic ketoacidosis (which occurs in poorly treated Type I diabetics), dietary ketosis is not dangerous and is an adaptation by the body to total starvation.

Many diets such as The Atkins Diet and other very low-carbohydrate diets are based around establishing ketosis for various reasons which are beyond the scope of this article. I only bring this up as most ketogenic diets set a carbohydrate intake level of roughly 30 grams per day (allowing some vegetables but little else) although I’ve never found support for that specific value.

I bring this up in the context of this article as many people start such diets with the specific goal of developing ketosis (again, for a variety of reasons). Since many books give the 30 g/day value for a ketogenic diet, folks get a little anxious about carb intakes that are higher than that.

However, strictly speaking, any diet with less than 100 g/day of carbohydrate will cause ketosis to develop to some degree (more ketones will be generated as carbs are lowered). I’d note that many ketogenic dieters use Ketostix to track ketosis, small sticks that measure urinary ketone levels. These are misleading for a number of reasons, not the least of which is that while ketosis (as defined by blood concentrations of ketones) may develop, urinary ketones don’t always show up, especially as carbs are raised to nearer the 100 g/day high end.

In any case, an intake of 15-50 grams per day of carbohydrate will still allow ketosis to develop and those ketogenic dieters attempting to ‘eat as few carbs as possible’ might want to consider that in the context of not only providing much needed food variety (at 50 g/day, even a small amount of fruit can often be fit in) but also in the context of the protein sparing issues I discussed above.

Getting to the point, although the physiological requirement for dietary carbohydrates is zero, we might set a practical minimum (in terms of preventing excessive body protein loss) at 50 grams per day. I’d note again that, within the context of The Rapid Fat Loss Handbook approach, carbs are limited to essentially trace amounts; however protein (which makes up the majority of the diet) is set high enough to limit muscle loss.

However, not everyone functions well in ketosis. They get brain fuzzed, lethargic and just generally feel awful. Even with weeks of being on a ketogenic diet, they never seem to adapt completely. That’s not a good recipe for long-term adherence to a diet or healthy functioning or training.

Tangentially, I’d note that this seems to be related to inherent levels of insulin sensitivity. Individuals with good insulin sensitivity, who typically run well on carbohydrates, tend to not do well on low-carbohydrate diets. In contrast, individuals with insulin resistance often do far better reducing carbohydrates and that often means going to ketogenic levels. Finally, some people seem to have the metabolic flexibility to do well with either diet. I address this issue in more detail in article Insulin Sensitivity and Fat Loss.

So what if people want to avoid ketosis? In general, assuming zero or very low levels of activity, an intake of 100-120 grams of carbohydrates per day will prevent the development of ketosis, just providing the brain with enough carbohydrates to function ‘normally’. So, for folks who want (or need) to just avoid ketosis, 100-120 grams per day will act as a practical limit. Again, this won’t quite work as a recommendation for people involved in high-intensity activity since not all of the incoming carbs will be available for the brain.

So, summing up mid-article, the absolute requirement for carbohydrates is zero grams per day. However, depending on protein intake, a practical minimum for carbs lies between 50 grams/day (if someone functions well in ketosis) to 100-120 grams per day (if they don’t function well in ketosis). Let me mention very specifically that I’m not suggesting those numbers are a recommended level, I’m simply using them to represent a practical minimum value.

As a final note, before addressing the issue of exercise, I want to note that the above values above don’t change significantly with body size (e.g. it’s one of the few places that an absolute number of carbs, rather than an amount set relative to bodyweight is appropriate). Most of the above discussion deals with the carbohydrate requirements of the brain which, for the most part, doesn’t change massively with body size. A 120 pound female and a 200 pound male have roughly similar carbohydrate requirements for their brains because brain size simply doesn’t differ that much between them.

The Impact of Exercise

So far I haven’t considered the impact of activity on all of this as this can affect daily carbohydrate requirements. I’d comment that all exercise is not the same and different types of activities will affect carbohydrate requirements very differently. The type, amount and intensity of activity will impact on carbohydrate requirements.

Typical low intensity aerobic/cardiovascular work doesn’t generally use a lot of carbohydrate. So if someone were only performing that type of activity (i.e. walking 3-5 times per week), there wouldn’t be any real need to increase carbohydrate intake over the above minimum. They might want to increase carbohydrates to higher levels than that (for various reasons) but, strictly speaking, they probably don’t need to.

The carbohydrate requirements for weight training actually aren’t that great. I did some rough calculations in The Ketogenic Diet and concluded that, for every 2 work sets (assuming a set length of 30-45 seconds) or so, you’ll need 5 grams of carbohydrates to replenish the glycogen used.

So if you did a workout containing 24 work sets, you’d only need about 60 extra grams (24 sets * 5 grams/2 sets = 60 grams) of carbohydrate to replace the glycogen used. So if you were starting at the bare minimum of 50 grams per day and were doing roughly 24 sets/workout, you’d need to consume an additional 60 grams (total 110 grams/day) to cover it. If you didn’t function well in ketosis and were starting at the 100-120 g/day, you’d increase to 160-180 g/day. I’d note that, for the average male lifter, this works out to about 1 g/lb or ~2 g/kg lean body mass carbohydrate per day

In this context, bodybuilding nutrition (much of which has been determined empirically over the years) has long recommended carbohydrate intakes ranging from 1 g/lb on fat loss diets to 3 g/lb for mass gains so we’re definitely in that range at this point. General recommendations for strength athletes by the nutrition mainstream are in the range of 5-7 g/kg or 2.2-3 g/lb so these values are all pretty consistent.

Higher intensity cardiovascular exercise is a little bit harder to pinpoint in terms of carbohydrate requirements and can vary pretty significantly depending on the intensities and volumes. A sprinter running 60m repeats isn’t using a lot of glycogen, a trained endurance athlete working near their lactate threshold for extended periods can deplete glycogen fairly completely in 1-2 hours. Even at lower intensities, the 2-6 hour sessions done by endurance athletes can completely deplete both muscle and liver glycogen stores on a daily basis.

Full skeletal muscle glycogen depletion for these athletes might represent 300-400 grams of total carbohydrate or more. For an average sized endurance athlete this might represent 3 g per pound or ~6 g/kg on a more or less daily basis. Under less extreme circumstances, carbohydrate requirements won’t be as high. And while current recommendations for endurance athletes are in the 7-10 g/kg (3-4.5 g/lb) range, studies show that most athletes consume closer to 5 g/kg (2.2 g/lb).

However, only the most highly trained athletes are going to be able to do that on a daily basis. Even with exercise, the average recreational trainee won’t have carb requirements near that level. Essentially, if competition athletes are getting sufficient carbohydrate intake at a level of ~5 g/kg (roughly 2 g/lb), I see little reason for the average individual to consume more or for people to recommend that they consume more.

I should note that the above sections assume that maintenance of muscle glycogen is the goal. Under some situations (generally fat loss), glycogen depletion, or maintenance of glycogen at a lowered level is the goal. This means that an athlete or dieter may deliberately under consume carbohydrates such that, over some time period, glycogen concentrations decline. In such a situation, where someone deliberately wanted to maintain muscle glycogen at lower levels, the above values would be too high since they are aimed at full glycogen repletion after heavy exercise.

Of course, there are also situations where dieters or athletes want to increase muscle glycogen levels far above normal; this will require higher carbohydrate intakes than the values above.

Is There a Maximal Level of Carbohydrate Intake?

Logically, a practical upper limit for carbohydrates intake would be a situation where they made up 100% of someone’s total energy intake. An average individual has a daily caloric intake in the realm of 14-16 cal/lb. Since carbs have 4 calories/gram, this would represent a maximum intake of roughly 4 grams/lb (8.8 g/kg). Of course, athletes involved in heavy training (who are burning far more calories than 14-16 cal/lb) have higher caloric (and hence carbohydrate requirements). But for the typical person at maintenance, a realistic upper limit would be ~4 g/lb and this would leave no room for either dietary protein or fat (without going over maintenance calories).

Of course, there are also situations where a dieter or athlete wants to super-compensate their muscle glycogen levels; that is load the skeletal muscle far above the levels which are normally maintained. This is often done by endurance athletes looking to improve performance and various cyclical diets (such as my Ultimate Diet 2.0) use glycogen compensation for anabolic (muscle building) purposes.

Generally speaking, to generate maximal levels of glycogen requires first depleting the skeletal muscle with the combination of heavy training and a low-carbohydrate diet. Given those conditions, carbohydrate intakes in the realm of 16 g/kg (a little over 7 grams/pound) of lean body mass can be tolerated over a 24 hour period. This probably represents a practical maximum for carbohydrate intake but it would only be achievable under this very specific situation.

Summing Up

So let’s sum up, looking at both practical minimum and maximum carbohydrate intakes under different circumstances. For illustrative purposes, after each of the g/lb recommendations, I’ll give an absolute number of carbohydrate, assuming an athlete with 160 pounds of lean body mass.

 

1. All values are in g/lb. To convert to g/kg, multiply by 2.2.
2. Note: If protein intake is sufficient, this amount of carbohydrate is not required.
3. All values above this line assume no exercise and do not change significantly with body weight.
4. Assumes a set length of 30-45 seconds.
   

Clearly the above represents a pretty drastic range of carbohydrate requirements, depending on the specifics. For a typical male with 160 pounds of lean body mass, daily carbohydrate intake could range from the physiological requirement of zero grams per day to a near maximum of 1120 g/day during a carb-load. Which makes it no wonder that people are confused.

Simply, the question “How Many Carbohydrates Do You Need?” has no singular answer. The goals of the person, the amount and type of activity, their individual needs (e.g. insulin sensitive vs. resistant, whether or not they function well in ketosis or not), their individual goals all determine how many carbs are ideal in the diet.

Examining Both Sides of the Debate

As noted, the usual argument goes that high-fat diets cause high-cholesterol, heart disease, cancer, obesity and the rest, as evidenced by the high incidence of those disease in modern diets (which are typically high in fat). But that’s a questionable conclusion to draw.

Modern diets are also high in carbohydrates (and mainly the highly refined, high GI, low-fiber stuff that the body often doesn’t handle well), low in fruits and vegetables, and generally contain the wrong types of fats (an excess of saturated and trans fats with insufficient amounts of healthy fats). Such an intake is typically coupled with inactivity, the folks eating them tend to be overweight/obese, smoking and alcohol play a role, etc. That is, there are a number of inter-related factors at work here.

Pinning the blame entirely on fat intake or expecting only a reduction in fat to fix the problem is disingenuous: there are a lot of variables at work here. Some research suggests that the entirety of the problem rests with excessive saturated fat intake with the other variables (activity, fruits and vegetables, etc.) playing a relatively minor role. It’s awfully hard to tease out all of the relationships when there are this many variables at play.

Similar comments can be made in terms of obesity. Fat is more calorically dense than carbohydrates and studies comparing high-fat (40%) to low-fat (25%) meals find that people tend to eat more in the higher fat conditions; this is usually referred to as passive over-consumption and leads to excess calorie intake. These studies have problems, mind you, but that’s beyond the scope of this article. The point does stand, though, that dietary fat is tasty (giving food mouth feel) and folks do tend to eat more of foods that taste good.

But while it’s common to blame obesity on high-fat diets, not all researchers agree. Some cultures have fairly high fat intakes but have no problems with obesity and researchers are starting to realize that fat isn’t the ONLY problem. Increasing intakes of refined carbohydrates (contributing large numbers of calories to the diet), decreasing activity, increasing portion sizes and other factors all contribute. You can’t dismiss an excessive fat intake as part of the obesity problem; it’s simply not the sole factor. I don’t want to get into a massive discussion of the carb versus fat debate in terms of caloric intake, preferring to focus on the health issues here.

The fact is that not all studies link a high fat intake to an increased risk of disease. For example, recent analyses of our ancestral diet (what we ate during 99.9% of our evolution) suggests a much higher fat intake and much lower daily carbohydrate intake. Exact numbers vary depending on what assumptions you use but carb intakes of 20-40% (most of which came from low GI, high fiber fruits and vegetables; grains were almost non-existent), fat intakes of 28-60% (which had a significantly different quality than our current diet), and protein intakes of 19-35% of total calories are the current best estimates.

Studies of extant hunter-gatherer societies show little incidence of any of the diseases of modern society and it’s thought that our evolutionary diet was NOT atherogenic (promoting heart disease) despite the high fat intake.

The reasons for this are many-fold, of course and that’s the key to keep in mind when you consider fat intakes and potential health problems. In our ancestral diet, fiber intakes were monstrous, averaging 100-150 grams per day. As well, despite the high fat intake, the source of that fat was far, far different than our modern intake. Much higher intakes of polyunsaturated and mono-unsaturated fats and far lower intakes of saturated fat were fairly typical. Activity levels were also much higher and folks generally stayed pretty lean. Alcohol intake was low or non-existent, as was smoking. Although our ancestors dealt with various stresses, they didn’t deal with the kinds of chronic stress that occurs in modern societies.

Related to this, studies of the Mediterranean diet have found few problems in terms of heart disease and all the rest despite a relatively high fat intake (40% of total calories). Although the reasons are, as always, multi-factorial some of the contributing factors are that the fat intake is primarily from mono-unsaturated sources (e.g. olive oil).

As well, a tremendous amount of fresh vegetables are typically consumed (with far less reliance on refined carbohydrates). Other factors such as activity, bodyweight, moderate alcohol intake and lowered stress levels probably play a role. Studies of the Alaskan Inuit show similar results, despite an extremely high-fat intake, heart disease is almost unheard of. This has typically been attributed to the high intake of fish oils but there may be genetic adaptations as well.

Of course, some studies on low-carbohydrates diets (which are typically high in fat) will show a big improvement in blood lipid levels; this is especially true for individuals with insulin resistance. I’d note that this effect primarily occurs when weight is lost; in studies of very low-carbohydrate diets where weight is gained, blood lipid levels often get much much worse.

Thus, whether or not you’re gaining or losing weight probably impacts on whether or not dietary fat is a health risk. I’d note that studies in cyclists find that high intakes of saturated fat don’t pose a health problem as long as the athletes are in calorie balance. As I mentioned above, activity (which will affect whether ingested dietary fat is stored or burned off) plays a big role here.

Studies in diabetics are finding that higher mono-unsaturated fat intakes (and lowered carbohydrate) intakes may be healthier than the converse. This, of course, only holds if calories are strictly monitored and controlled to avoid weight gain. When weight is gained, from nearly any dietary approach, blood sugar control in diabetics worsens.

Of course, there’s a flip side to the anti-fat dogma and reducing fat to extreme levels can cause its own set of problems. First and foremost, most people find extremely low-fat diets to be tasteless and this tends to limit adherence in the long-term (as I mentioned above, high-fat diets tend to be very tasty and people frequently eat too much).

And while caloric intake typically goes down in the short-term, folks frequently end up increasing caloric intake because they are hungry all the time. Dietary fat slows gastric emptying (keeping food in the gut longer) although some work suggests that this effect is lost with chronically high-fat diets. Extremely low-fat diets tend to leave people hungrier for this reason.

There is also evidence that the fat-soluble vitamin absorption may be impaired when fat intake is taken too low. And while total cholesterol typically decreases when fat intake is lowered, the decrease occurs in both the good (HDL) and bad (LDL) sub-fractions so overall health risk may not be improved. From a body recomposition or performance standpoint, some studies show a lowering of testosterone with very low fat diets.

There is another set of issues that crops up as well. Again, it relates to the simple fact that people have to eat something. In reducing fat intake, most people increase carbohydrate intake. Most researchers would say that this is just fine as long as the increase comes in the form of unrefined, high fiber, complex carbohydrates. I would say that most researchers need to get out of the lab and look at the real world for a while.

The simple fact is that the majority of people who reduce fat do NOT increase carbohydrate intake from unrefined, high-fiber, complex sources. This is especially apparent in the US (I can’t speak for other countries) where companies rapidly jumped on the ‘fat is bad’ bandwagon and brought tons of ‘low-fat’ high-carbohydrate sources that were highly refined to market.

Such foods may have as many, if not more, calories than the same higher-fat items. Even when they don’t, humans play a cute psychological game, tending to eat more of a given food when they are told it’s low or no-fat.

Recent studies are finding that, when carbs are increased from those sources, other problems show up. In addition to the changes in blood cholesterol I mentioned above (both the good and bad subfraction decrease), the increase in refined carbohydrate intake causes an increase in blood triglyceride levels and small LDL particles; both of which are independent risk factors for heart disease and all the rest. The chronically high insulin levels which commonly occur with such a diet cause other problems including insulin resistance and all of the issues that accompany it.

I should probably note, and this could certainly be an entirely separate article, that the new scapegoat for obesity and all of the health problems in the world is excessive carbohydrate intake, with a lot of the focus on insulin release. I don’t have space here to address that side of the argument, a future topic for another day.

Sufficed to say that while there is certainly an element of truth to this (in that excessive intakes of any nutrient, and that includes refined carbohydrates, is bad), it’s still true that simplistically arguing that ‘fat is good and carbs are bad’ is just as moronic as arguing that ‘carbs are good and fat is bad’. Again, it depends on the context.

Summing Up

Now, I want to make it very clear that I’m not trying to make this either a pro-fat or anti-carbohydrate article or trying to make a low-carbohydrate diet the default choice for anybody. My point is simply that the idea that ‘fat is bad’ and ‘carbs are good’ (or the opposite) is too simplistic to be meaningful.

Not all fat is bad and not all carbs are good. The source, the composition of the rest of the diet, the total amounts you’re eating of each, your activity level and other variables all factor in. Whether you’re talking about health risk or obesity, you can’t simply pin the blame on one factor or the other.

So, under conditions of high caloric intake, with a high intake of refined carbohydrates (meaning chronically high insulin levels), poor quality fat choices (too much saturated fat and/or too little unsaturated fats), little activity, minimal fruit and vegetable intake, etc. a high-fat intake is probably very detrimental from a health standpoint. Sadly, this describes a fairly typical diet in the modern world (especially the US).

In contrast, with reduced or even controlled caloric intake (such that bodyweight goes down or is maintained) and most of the fat coming from unsaturated sources (note: excessive polyunsaturated fats has its own set of problems), a high fruit and vegetable intake, reasonable activity levels, keeping body fat levels down, etc. higher fat intakes may be no problem at all. In some situations, an increased fat intake (again, from healthy sources within the context of activity and a high fruit and vegetable intake) may be beneficial compared to the alternatives (e.g. increasing carbohydrate intake).

In this article, I want to look at carbohydrate and fat intake in terms of the various arguments and debates that tend to surround them.

The main controversy here revolves around what amounts of carbohydrates and/or fat are ideal, healthy, recommended, etc. and that’s what I’ll focus on. I’m not going to deal with body composition explicitly in this article, I’ll save that for another day.

Two (or Three) Dietary Camps

Generally, folks fall into one of two camps regarding whether they think carbohydrates or fats are good or bad. For a couple of decades now, the mainstream of dietary advice has been more or less stuck in the mindset of ‘fat is evil and ‘carbohydrate is good’.

Various attempts to promote so-called ‘high-fat’ or ‘low-carb’ diets have usually been shot down as fads although there is increasing research evidence that, at least for some individuals (usually those with insulin resistance) higher fat intakes and lowered carbohydrates may be both beneficial and preferred.

However, for the most part, I’d say that mainstream dietitians are still on the carbs = good, fat = bad bandwagon with higher fat/lower carbohydrate diets being relegated to the diet ‘fringe’.

Both groups can bring impressive (or at least impressive looking) data to the table but, as usual, extreme stances are invariably incorrect and the truth lies somewhere in the middle; this particularly debate is no different.

The third group (and the one I put myself in) recognizes that whether or not carbohydrates or fats are ‘good’ or ‘bad’ depends on the context. The source of the carb or fat, the rest of the diet, the goal of the individual, genetics, activity, etc. all factor into this issue. So while it may be convenient to give simplistic recommendations of the ‘X is bad, Y is good’ variety, simple in this case tends to be incorrect.

Perhaps the most succinct way of describing what I’m going to detail is that there are no good or bad foods only good or bad diets. That is, within the context of one type of diet or individual situation, a specific food may be excellent; under other conditions it may be a poor choice.

What does the Body Require?

So that some of my comments will make sense, I need to cover a smidgen of nutrient physiology, mainly having to do with the issue of carbohydrate ‘requirements’ (a topic I cover in detail in How Many Carbohydrates Do You Need).

As I think I’ve managed to work into every book I’ve ever written, there is no strict physiological requirement for carbohydrates (this factoid is often used by the low-carb diet groups as part of the rationale for their dietary approach).

Most tissues in the body can readily use fatty acids for fuel just as easily as glucose. There are a few tissues such as the renal medulla, red blood cells and one or two other that can only use glucose. However, those cells essentially make their own glucose by recycling lactate (produced from glucose metabolism) back into glucose.

The brain is in its own weird category. Under most conditions, it relies exclusively on glucose. And while it can’t use fatty acids directly, it can use a fatty acid derived fuel in the form of ketone bodies. After roughly three weeks of adaptation to using ketones, the brain may only need 25 grams/day of glucose or so, which can be made by the body (in the liver and kidney) from sources such as lactate, pyruvate, amino acids and glycerol.

Even the American Dietetic Association bible, the RDA Handbook, states that there is no requirement for dietary carbohydrates. Any decent nutrition or physiology book will state the same. Despite this basic biological fact, many researchers and diet authorities still insist that the majority (50-60% or more) of the human diet should come from carbohydrates.

I’ve seen papers where researchers point out that the body requires no carbohydrates which then go on to say that a proper diet should contain at least 50% carbohydrates. It doesn’t make much sense.

At the same time, outside of a small essential fatty acid requirement (a few grams per day from the fish oils, EPA/DHA), fats aren’t truly required by the body either. All of the tissues I mentioned above will use glucose if you provide it (the heart is an exception, almost exclusively relying on fatty acids for fuel) and the body can make fatty acids out of other sources if need be (this pathway isn’t utilized massively in humans, although a few conditions will make it relevant).

So, outside of the small essential fatty acid requirement, one could make an argument for there being no physiological requirement for fats either.

What does the body then require on a day to day basis if there is no real requirement for either carbohydrates or fats? Well, outside of the basics like water and air, roughly eight amino acids are essential to get from the diet, there’s the small essential fatty acids requirements and of course vitamins and minerals. Everything else, strictly speaking is optional.

I would note that, to avoid starving to death, sufficient calories will be required. Since it’s generally unrealistic to consume your entire daily caloric requirement from protein, that means that carbs, fats, or a combination of the two, will generally be needed to supply sufficient energy to the body.

But, as noted above, most tissues in the body show a great deal of flexibility, using carbs when they are available and fats when carbs aren’t available. Note also that the body has its own store of fuel, primarily in the form of body fat that is mobilized when sufficient amounts of other nutrients aren’t available.

So Why Do Most Argue that Carbs are Good and Fats are Bad?

Despite the fact that there is no physiological requirement for carbohydrates in the human diet, the most common dietary recommendation in modern times is generally to reduce fat intake and increase carbohydrate intake. I’m going to address the issue starting from that standpoint.

A good question might be why is this stance taken. While I can’t read the minds of these folks (and I hate to contribute to grain lobby USDA conspiracy theories), I think the reasons is actually fairly simple: we have to eat something.

There’s usually a limit to how much protein can be reasonably consumed (and most authorities seem to be against ‘high’ protein intakes as well) so that means that the rest of the diet (in terms of energy) must come from either carbohydrate or fat.

In the 70’s, the stigma against dietary fat started to develop and it all pretty much went from there. Fat was implicated as the cause of heart disease, stroke, obesity, you name it and excessive fat intake was blamed.

Since people have to eat something and because of the general stigma against a high fat intake (some of which is warranted, some of which isn’t), policy makers recommend a high-carbohydrate intake by default.

The bigger question is whether or not this is a scientifically defensible position.

I’ll address this issue in more detail in Carbohydrate and Fat Controversies: Part 2