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.

In theory, you can make arguments for or against any of these approaches in terms of superiority. In the real world, it’s not quite that simple. You can always find folks (and this is true whether they are bodybuilders or just general dieters) who either succeeded staggeringly well or failed miserably on one or another approaches.

Before going on, I want to mention that protein recommendations tend not to vary that significantly between diets and most of the arguments tend to revolve around the varying proportions of carbohydrate and fats in the diet and that’s what I’ll be focusing on here. Simply, I don’t consider low-protein fat loss diets in the equation at all for the simple fact that they don’t work for anybody but the extremely obese. Any dieting bodybuilder or athlete needs 1-1.5 g/lb lean body mass of protein on a diet. Possibly more under certain circumstances.

My general experience has been that individuals who respond very well to high-carbohydrate/lower fat diets tend to do very poorly on low-carb/higher-fat diets. They feel terrible (low energy and a mental fog that never goes away), don’t seem to lean out very effectively and it just doesn’t work.

This cuts both ways: folks who don’t respond well to higher carbs do better by lowering carbs and increasing dietary fat. Sometimes that means a moderate carb/moderate fat diet, sometimes it means a full blown ketogenic diet. I should also note that some people seem to do just as well on one diet as another.

Some of this may simply be related to adherence although this tends to be less of an issue in bodybuilders (who take obsessiveness to a new level). Carb-based diets make some people hungry even if they follow all the ‘rules’; so they eat more and don’t lose fat effectively. For many of those people, reducing carb intake allows better calorie control in the long-term. People who hate moderation tend to like cyclical ketogenic diets, they can handle no-carbs during the week and massive carb-ups on the weekend; moderate carbs drive them crazy.

But how does all of the above help the neophyte dieter looking to diet down. Put differently, how can someone know ahead of the fact what diet might be optimal for them? Current research is starting to explore a link between diet and genetics and suggesting biological differences in how people respond to diet; that might explain some of the real-world results I described above.

With regards to fat intake, studies have identified what researches call low and high-fat phenotypes (phenotype is just a technical word for the interaction between your genetics and your environment) (1). Some people appear to be better able to increase fat burning in response to higher fat intakes; they stay lean in the face of such an intake. Others, however, do no such thing. Other aspects of metabolism and appetite were associated with being either a high- or low-fat phenotype.

Unfortunately, no practical way of determining which one you might be ever came around. It was also never exclusively determined if the effect was due to inherent biology or simply adaptation to a habitual diet. But the point still stands, biologically, some people seem better able to increase fat oxidation in response to higher fat intakes than others. I think this goes part of the way to explaining the response (good or bad) to high-fat ketogenic diets. People who upregulate fat oxidation well tend to thrive on them; people who don’t just get bloated and don’t lose fat well.

More recently, an interaction between diet effectiveness and both insulin sensitivity and insulin secretion after a meal has been proposed (2). Noting that all of the research to date has been on obese individuals (not dieting bodybuilders), I still think it explains some of what is going on. As well as allowing us to predict ahead of time which diet someone might do best on.

A Very Brief Primer on Insulin Secretion and Sensitivity

To understand the research I want to talk about next, I need to briefly discuss two different but somewhat related aspects of insulin metabolism: insulin sensitivity/resistance and insulin secretion.

As I imagine all of the readers of this know, insulin is a storage hormone released in response to eating with carbohydrates having the largest impact on insulin secretion, protein having the second greatest and fat having little to no impact on insulin secretion. Insulin sensitivity refers to how well or poorly the body responds to the hormone insulin. Individuals who are insulin resistant tend to have higher baseline insulin levels because the body is releasing more in response to try and overcome the resistance.

And while a great majority of insulin resistance is determined by lifestyle (training and diet play a huge role, as does body fatness), so do genetics. At the same bodyfat level, insulin sensitivity can vary nearly 10 fold for genetic reasons. So it’s possible that even lean athletes and bodybuilders could have some degree of genetic insulin resistant (I’ll talk about how to determine this at the end of the article). As it turns out, individuals also differ in how much or how little insulin they release following a standardized meal; some people release more insulin than others in response to a meal. While this can be related to baseline insulin sensitivity, it doesn’t have to be.

It turns out that both issue relate to fat/weight gain or loss (2). In contrast to what is generally believed, good overall insulin sensitivity tends to correlate with weight/fat gain and insulin resistance is thought to be an adaptation to prevent further fat/weight gain. However, some research suggests that a tendency to release too much insulin in response to feeding may predispose people towards weight/fat gain. One huge confound in all of this, mind you, is that high insulin secretion tends to make people eat more. Studies of diabetics find that decreasing insulin secretion with drugs tends to cause a spontaneously lower food intake (2).

The Impact of Insulin Sensitivity or Insulin Secretion on Response to Different Diets

While the research is in its infancy, there have been studies examining the weight loss response relative to either insulin sensitivity or insulin secretion. For the most part, no major difference in terms of weight loss has been found in subjects with different insulin sensitivities (2). However, at least one study found that the specific diet given interacted with baseline insulin sensitivity to determine the magnitude of weight loss (3). In that study, obese women with either high or low insulin sensitivity were placed on either a high carb (60% carb, 20% fat) or low carb (40% carb, 40% fat) diets.

So there were four groups: high carb/insulin sensitive, high carb/insulin resistant, low carb/insulin sensitive, low carb/insulin resistant. The results were intriguing: insulin sensitive women on the high carb diet lost nearly double the weight as insulin sensitive women on the low-carb diet. Similarly, insulin resistant women lost twice the weight on the low-carb diet as on the high carb diet. Unfortunately, it’s not clear what caused the divergent results. The researchers mentioned a gene called FOXC2 which is involved in energy expenditure and found that it was upregulated in the individuals who responded best to diet; further research into this topic is needed (3).

Even less data relates to insulin secretion status and diet although a recent study suggests that it may (4). In that study, subjects were given either a high glycemic load (60% carbs, 20% protein, 20% fat) or a low GL diet (40% carbs, 30% protein, 30% fat diet) and weight loss was examined relative to baseline insulin secretion. In that study, subjects with high insulin secretion lost more weight on the low glycemic load diet while subjects in the low insulin secretion group lost slightly more on the high glycemic load diet.

Getting to the Point

Overall, I think the limited data available on both high and low fat phenotypes as well as how individuals with differing baseline insulin sensitivity/secretion respond to diets supports the observations occurring in the real world in terms of both subjective feelings on a given diet as well as the weight/fat loss response. So how can we put this to use?

Unfortunately, there’s no easy way to see if you’re a high or low fat phenotype so I’ll focus on insulin sensitivity. There are a lot of complicated and impractical ways to determine insulin sensitivity and insulin secretion. All involve blood work and looking at either baseline insulin or blood glucose or how insulin changes in response to a meal.

However, in practice, there are signs as to whether you have good insulin sensitivity or not and possibly whether you over-secrete insulin. Here’s two very simple questions to ask yourself regarding your response to diet.

1. On high-carbohydrate intakes, do you find yourself getting pumped and full or sloppy and bloated? If the former, you have good insulin sensitivity; if the latter, you don’t.
2. When you eat a large carbohydrate meal, do you find that you have steady and stable energy levels or do you get an energy crash/sleep and get hungry about an hour later? If the former, you probably have normal/low levels of insulin secretion; if the latter, you probably tend to over-secrete insulin which is causing blood glucose to crash which is making you sleepy and hungry.

I consider it most likely that superior bodybuilders couple excellent insulin sensitivity with low insulin secretion in response to a meal. This would tend to explain why bodybuilders have often gravitated towards high carb/low-fat diets and been successful on them.

At the same time, mediocre bodybuilders frequently get less than stellar results from that same diet. Lowering carbs and increasing dietary fat seems to be more effective in that case some of the low-carb bulking strategies out there probably work better for those individuals. The same goes for fat loss. Cyclical low-carb diets such as my Ultimate Diet 2.0 or the more generic cyclical ktogenic diet (CKD) described in my first book The Ketogenic Diet allow such individuals to briefly enjoy the benefits of heightened muscular insulin sensitivity.

Putting it Into Practice

If you have good insulin sensitivity and low insulin secretion, odds are you will do well with a traditional bodybuilding type of diet which means high protein, highish carbs and low fat. Let’s say you’re consuming 1 g/lb of protein at 12 cal/lb. That’s 33% protein. If you go to 1.5 g/lb, that’s 50% protein. That leaves you with 50-67% of your calories to allocate between fat and carbohydrate. 15-20% dietary fat is about the lower limit as it becomes impossible to get sufficient essential fatty acids below that intake level. So, at 1 g/lb, your diet will be roughly 33% protein, 47-52% carbs (call it 45-50%) and 15-20% fat. If protein goes to 50% of the total, carbs should come down to 35% of the total with 15% fat.

If you’re not insulin sensitive and/or have high insulin secretion, a diet lower in carbs and higher in fat (don’t forget that protein can raise insulin as well) is a better choice. Assuming, again, 40% protein, a good starting place might be 40% protein, 20-30% carbs and 20-30% fat. A further shift to a near ketogenic (or cyclical ketogenic) diet may be necessary, 40% protein, 10-20% carbs and the remainder fat may be the most effective. If protein is set higher, up to 50% protein, carbs would be set at 10-20% with the remainder (20-30%) coming from dietary fat.

Summing Up

Hopefully the above has given you some insight into choosing what might be an optimal fat loss diet without having to go through so much tedious trial and error. However, please don’t treat the above as more than a starting point. Adjustments to diet in terms of calories or nutrient intake should always be based on real world fat loss. You should be tracking your fat loss every 2 weeks (4 at the most); if you’re not losing at a reasonable rate (1-1.5 lbs fat loss/week), you need to adjust something.

Bio: Lyle McDonald received his BS in physiology from UCLA in 1993 and has been obsessed with all aspects of human performance (training, nutrition, supplements) since then. He has written extensively about fat loss, especially low carbohydrate dieting. He is currently working on a book covering all aspects of protein nutrition for athletes as well as an approach to getting rid of stubborn bodyfat. His website is http://www.bodyrecomposition and his books can be ordered there by clicking on the store link.

References:

1. Blundell JE, Cooling J. High-fat and low-fat (behavioural) phenotypes: biology or environment? Proc Nutr Soc. 1999 Nov;58(4):773-7.
2. Pittas AG, Roberts SB. Dietary composition and weight loss: can we individualize dietary prescriptions according to insulin sensitivity or secretion status? Nutr Rev. 2006 Oct;64(10 Pt 1):435-48. Review.
3. Cornier MA et. al. Insulin sensitivity determines the effectiveness of dietary macronutrient composition on weight loss in obese women. Obes Res. 2005 Apr;13(4):703-9.
4. Pittas AG et. al. A low-glycemic load diet facilitates greater weight loss in overweight adults with high insulin secretion but not in overweight adults with low insulin secretion in the CALERIE Trial. Diabetes Care. 2005 Dec;28(12):2939-41.

In this chapter, I want to give readers a very brief and simplified overview of human metabolism and nutrient use. Which, for those who know a lot about the topic will realize, is an understatement of vast proportion. The complexities of human metabolism can and do fill up hundreds of pages in physiology books and this chapter should be taken with that in mind.

The Basics: Energy and Building Blocks

Very simplistically speaking, we can divide the uses of the nutrients (discussed last chapter) into three categories, of which I only really want to talk about two. One category, which I won’t discuss much has to do with the vitamins and minerals which both act, essentially, as nuts and bolts in the body. They fulfill any number of different roles; depending on which one you’re talking about. While critical to human health, they simply aren’t that important to the topic of this book. If you’re interested, go get yourself a book on vitamins and minerals and go to town. All I’m going to say is that you should make an effort to ensure your vitamin and mineral intake. A basic one-per-day multivitamin should probably be good “nutritional insurance” for everyone, the obsessed can look at versions containing mega-doses or what have you of the different nutrients.

The second category is for use as building blocks. Most parts of the human body are in a constant state of breakdown and buildup and nutrients must come in to the body to provide building blocks for those processes. One I imagine all readers are familiar with is that of calcium (a mineral) being the building block for bones. Additionally, skeletal muscle, organs and many hormones have amino acids (coming from protein) as their building blocks. As well, both fats and cholesterol play a role as a building block for cell membranes and a few other substances in the body.

The third category, and the one I’ll spend the most time on in this chapter, is as an energy (fuel) source. Even as you sit reading this and growing bored, your body is using energy at some rate. So your brain, your heart and other organs, skeletal muscle, liver and even your fat cells are using energy, although the rates at which each uses energy varies from high (e.g. brain, liver) to extremely low (e.g. fat cells). Surprisingly and quite contrary to common belief, at rest skeletal muscle doesn’t burn that many calories. The idea that adding muscle mass will turn you into a calorie burning inferno is simply incorrect.

Where Does the Energy Come From?

So where does that energy come from? At the lowest level of cellular function, the only form of energy that your cells can use directly is something called adenosine triphosphate (ATP). I doubt that factoid is very helpful to readers except perhaps as the answer to a Trivial Pursuit or game show question. If you happen to sit around having polite conversation about ATP, please send me an email: I want to hang out with you.

Of more use to us, the body generates ATP from the burning (oxidation or combustion to use a more sciency term) of either glucose from carbohydrate or fatty acids from fats. Under specific circumstances protein can be used to produce ATP, either directly or via the conversion to either glucose or fat (usually protein is converted to glucose to be used for fuel). I’ll come back to this below.

With a few exceptions that I’ll talk about in a second, every tissue in your body can use either carbohydrate or fat for fuel. What determines which they use? For the most part, it’s the availability of carbohydrates: when carbs are available (because you’re eating plenty of them), those tissues will use carbohydrates, in the form of glucose, for fuel. When carbs are not available (because you’re restricting them), the body will switch to using fat for fuel. That fat can either come from your diet or from the fat stored on your butt or stomach. This has another implication that is often forgotten in weight/fat reduction programs: when you eat more carbohydrates, your body uses less fat for energy; when you eat less carbohydrates, your body uses more fat for energy.

So what about those exceptions? A few tissues in your body such as the brain/central nervous system and one or two others can’t use fatty acids for fuel; they can only use glucose. The brain is the main one I want to talk about here. It’s usually (and incorrectly) stated that the brain can only use glucose for fuel, and this is true if you only consider glucose, amino acids, and fat as potential fuel sources. But this leaves out a fourth, extremely important, fuel source: ketones (also known as ketone bodies). Ketones are made from the breakdown of fat in the liver and function as a fat-derived fuel for the brain during periods of starvation/carbohydrate restriction.

I’ll talk about starvation in more detail in a second but I want to mention that, after a few weeks in ketosis (a state where ketones build up in the bloodstream such that fuels such as the brain start using them for energy), the brain can derive 75% of its total energy from ketone metabolism. The other 25% comes from glucose.

So Aren’t Carbohydrates Essential?

At this point you may be slightly confused about the role of carbohydrates in the diet. In the last chapter, I stated that carbohydrates weren’t an essential nutrient and above I mentioned that a few tissues can only use glucose and that even the brain gets about 25% of its total fuel requirements from glucose after adaptation to ketosis. So if those tissues still require glucose for energy, you may be wondering how carbohydrates aren’t essential in the diet. Remember from the last chapter what the two requirements of an essential nutrient are

• That nutrient is required for the proper function of the body.
• The body can’t make that nutrient in sufficient quantities.

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. 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.

So how is the glucose made? The answer is a biochemical process with the unwieldy name of gluconeogenesis, which simply means the making of new glucose. This process primarily occurs in the liver. When necessary, the body can make glucose out of a number of other substances including glycerol (which comes from fat metabolism), lactate and pyruvate (which comes from carbohydrate metabolism), and certain amino acids (from protein).

Which brings me back around to the topic of protein as a fuel source for the body. Readers may have read that “carbohydrates spare protein” and this is part of the basis for that claim: when carbohydrates are being eaten in sufficient quantities, the body has no need to break down protein for fuel. By extension, when carbohydrates are being restricted for whatever reason, some proportion of protein will be used to make glucose, leaving less to be used for building blocks. This has an important implication for dieting, namely that protein requirements go up when you’re restricting either calories or carbohydrates.

What About Starvation?

Now seems like as good of a time to talk about starvation, the consumption of zero food. I should mention that therapeutic starvation (as it was called) was tried during the middle of the 20th century for weight loss, frequently causing rather rapid losses of weight. But it had an unfortunate problem, which I’m going to address below. For now, let’s look at starvation and what happens.

So let’s say you stop eating anything and look at what happens (a much more detailed examination of this and many other topics can be found in my first book The Ketogenic Diet). Over the first few hours of starvation, blood glucose and insulin levels both drop. This signals the body to break down glycogen (stored carbohydrate) in the liver to release it into the bloodstream. As well, the body starts mobilizing fat from fat cells to use for fuel. After 12-18 hours or so (faster if you exercise), liver glycogen is emptied. At this point blood glucose will drop to low-normal levels and stay there. Blood fatty acids will have increased significantly by this point.

After a day or so, most cells in the body, with a few exceptions, are using fatty acids for fuel. Obese individuals may derive over 90% of their total fuel requirements from fat while leaner individuals may only derive about 75% of the total from fat. So far so good, right, the body is mobilizing and utilizing an absolute ton of fatty acids for fuel: 90% of your total energy expenditure if you’re fat and 75% if you’re lean (I’ll talk about what fat and lean is in another chapter).

There must be a drawback and here it is: the few tissues that require glucose are getting it via gluconeogenesis in the liver. As above, gluconeogenesis occurs from glycerol, lactate, pyruvate and amino acids. Now, if the person isn’t eating any protein, where are those amino acids going to have to come from?

That’s right, from the protein that is already in the body. But recall from last chapter that there really isn’t a store of protein in the body, unless you count muscles and organs. Which means that, during total starvation, the body has to break down protein tissues to provide amino acids to make glucose. The body starts eating its own lean body mass to make glucose to fuel certain tissues. This is bad.

Now, as fatty acids start to accumulate and be burned in the liver, ketones will start to be produced. Initially, for reasons totally unimportant to this book, muscles will use the majority of ketones that are produced. As I mentioned above, after a few weeks, the brain will adapt so that it is using ketones and deriving most of its fuel from them; the small remainder comes from the glucose being produced via gluconeogenesis.

Now, the adaptation to ketosis occurs for a profoundly important reason. Once again, much of the glucose produced in the body is from amino acids which are coming from the protein in muscle (and to a lesser degree, organs). If such a breakdown continued in the long term, so much muscle would be lost that the individual who was starving would be unable to move. Quite in fact, the loss of too much lean body mass (muscle and organs) causes death. The shift to using ketones decreases the need to break down body protein to make glucose.

As I mentioned above, therapeutic starvation was often used in the cases where rapid weight loss was needed. And while it did generate rather high levels of weight and fat loss, it had as a problem the loss of excessive body protein. So researchers decided to find a way to try and generate similar levels of weight/fat loss while sparing LBM. And that’s the topic of the next chapter.