Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
19 May

A Metabolic Paradigm Shift, or Why Fat is the Preferred Fuel for Human Metabolism

There’s a good reason so many people (mostly the sugar-burners, whose disparate group includes fruitarians, veg*ans, HEDers, body-builders, most MDs, the USDA and virtually every RD program in the country) can’t seem to grasp why a lower carb, Primal approach to eating is a better choice for health and fitness: their fundamental paradigm – the core theory that underpins everything else in that belief system – is flawed. They remain slaves to the antiquated notion that glucose is the king of fuels, so they live their lives in a fear of running low. The truth is, fat is the preferred fuel of human metabolism and has been for most of human evolution. Under normal human circumstances, we actually require only minimal amounts of glucose, most or all of which can be supplied by the liver as needed on a daily basis. The simple SAD fact that carbs/glucose are so readily available and cheap today doesn’t mean that we should depend on them as a primary source of fuel or revere them so highly. In fact, it is this blind allegiance to the “Carb Paradigm” that has driven so many of us to experience the vast array of metabolic problems that threaten to overwhelm our health care system.

It boggles my mind that such a large segment of the so-called health and fitness community would continue to defend high carbohydrate diets with such tenacity. It should all be very obvious by now. The studies keep piling up indicating that carbohydrate intake is the major variable in determining body composition and that excess glucose from carbohydrate intake (especially from processed grains and sugars) is the primary culprit in obesity and in many disease processes. It follows logically that if you can limit carb intake to a range of which is absolutely necessary (and even up to 50 grams a day over) and make the difference up with tasty fats and protein, you can literally reprogram your genes back to the evolutionary-based factory setting you had at birth – the setting that offered you the opportunity to start life as a truly efficient fat-burning organism and to continue to do so for the rest of your life as long as you send the right signals to your genes. Becoming an efficient fat-burner is the major premise of the Primal Blueprint eating and exercise strategies.

But logic doesn’t rule when you are stuck in the Carb Paradigm, so I still see some misguided bloggers decrying the Primal Blueprint eating strategy as potentially harmful for its relatively low carb intake or stating that my advice to “generally keep carbs under 150 grams a day unless you’re an athlete” is ridiculous. How many more times do I have to overhear a trainer advising a still-portly client to “eat 5 or 6 small meals throughout the day, always with some carbs, so you keep your blood sugar up and don’t go into starvation mode.”? It’s time to stop this nonsense and reframe the current views of human metabolism to accurately reflect the two and a half million years of evolution that shaped the current human genome – a perfect DNA recipe that fully expects us from birth to function largely on fats.

It’s time for a Metabolic Paradigm Shift within the health and fitness world.

The Faulty Carb Paradigm “Logic” Goes Something Like This

The basic underlying assumption is that glucose is the preferred fuel of most cells; BUT, because we can’t store very much glucose (as glycogen in liver and muscles), we need to provide a continuous source of glucose in the form of exogenous carbohydrate (high carb meals) to keep the brain, blood, and certain organs humming along and the muscles primed for activity. AND, if we don’t feed ourselves enough carbohydrate every few hours, our blood sugar will drop and we’ll go into “starvation mode” and cannibalize our precious muscle tissue. AND any lack of regular glucose refilling (i.e. skipping a meal or fasting) will cause cortisol to rise, which will have additional deleterious effects. FURTHERMORE, an excess of glucose in the bloodstream is known to raise insulin and will predispose excess calories (from all sources) to be stored as fat. THEREFORE, we should also be doing a lot of moderate-to-heavy cardio or lifting activity most days to burn off this excess stored body fat. HOWEVER, if we want to be ready and able to exercise frequently and strenuously to burn off our stored fat, we need to eat lots of complex carbohydrates between workouts to refill our glycogen stores. And ULTIMATELY, the only way to lose weight is to restrict calories (calories in<calories out), BUT if you’re working out regularly, it’s almost impossible to maintain a calorie-restricted regimen and still be able to work out hard enough to burn appreciable calories. Sheesh.

Sure, there are exceptions, like the driven and genetically gifted types, who can train long hours, refuel on carbs and not add much body fat (hey, I was one). But unless you love to work out incessantly and have really lucky familial genes, the Carb Paradigm is an unsustainable and ridiculous literal and figurative treadmill, a self-fulfilling prophecy for most people who tend to gain weight steadily and insidiously over the years and wonder why. If you are one of the 60+% of the American population who is overweight, the above scenario plays itself out because you have spent your life programming your genes in the direction of being an effective sugar burner and, as a result, have become dependent on a fresh supply of sugar (carbs) every few hours. Naturally, in the presence of all that glucose, and provided you actually do some exercise, your genes will eventually get the signals to up-regulate the enzyme systems, pathways and receptors involved in sugar-burning and fat storage and they’ll down-regulate all those involved in accessing and burning fat for energy. Of course, that doesn’t make it right, but it sure makes it appear as if glucose is king. What makes it worse, if you don’t exercise, you head down the path to insulin resistance and/or obesity.

The Problem: The Basic Assumption of the Carb Paradigm is Wrong

Glucose is not the preferred fuel of muscle cells under normal human resting metabolic conditions or even under most normal human movement patterns (exercise). Fat is. Sure, given an unlimited supply of glucose and regular refilling of glycogen stores, skeletal muscle will burn through it during exercise the same way a fire burns through kindling when that’s all you have to offer. The body can shift carbohydrate oxidation to keep up with intake. But skeletal muscle can burn fat with great efficiency (and far less oxidative fallout) at relatively high outputs for very long bouts. Cardiac muscle actually prefers ketones, and the brain can run just fine (maybe even optimally) on a blend of ketones and minimal glucose.  Our survival as a species has depended on these evolutionary adaptations away from glucose dependency. Entire civilizations have existed for ages on what is practically a zero-carb diet. Think about this: there is actually no requirement for any “essential dietary carbohydrates” in human nutrition. It’s possible to live a very long and healthy life never consuming much – if any – in the way of carbs, provided you get adequate dietary protein and fat. The same can’t be said for going too long without protein or fat. Cut too far back on either of those macronutrients and you will eventually get sick and die.

The Evolutionary Model

Fat and protein were the dominant macronutrients (when food was even available) over the majority of our two-and-a-half million years as evolving humans. The lack of regular access to food and a scarcity of carbohydrates for much of this time necessitated that we adapt efficient pathways to readily store and access body fat for energy if we were to survive day-to-day and generation-to-generation. Our movement patterns were such that we never required large amounts of glucose or that we needed to store very much glycogen. It was predominantly fats, ketones and the minimal infusion of glucose via gluconeogenesis that got us here. Dietary carbs were insignificant. In fact, when you consider how ridiculously small the body’s glycogen reservoirs are, you understand that it would have been impossible for us to survive as a species if glucose were truly the “preferred” fuel. The liver, the main back-up glycogen/glucose storage facility for the brain and other glucose-burning organs, can only store about 100 grams of glycogen. Less than a day’s worth. Your muscles can only hold another 350-500 grams, barely enough to run for 90 minutes at a reasonable clip, and that glycogen isn’t even available to provide fuel for the brain. Meanwhile, we have a virtually unlimited storage capacity for fat (like 100,000 grams or close to a million calories on some people). The reason glycogen storage wasn’t necessary is because, between our copious fat storage capability, easy access to fats as fuel, gluconeogenesis and ketones, we just didn’t need much. Evolution tends not to reward structures or functions that take up unnecessary space or waste energy.

So How Much Glucose Do You Really Need?

Much less than most people assume. At any one time, the total amount of glucose dissolved in the bloodstream of a healthy non-diabetic is equivalent to only a teaspoon (maybe 5 grams). Much more than that is toxic; much less than that and you pass out. That’s not much range for a so-called “preferred” fuel, is it? Several studies have shown that under normal low MET conditions (at rest or low-to mid- levels of activity such as walking and easy work) the body only needs about 5 grams of glucose an hour. And that’s for people who aren’t yet fat-adapted or keto-adapted. The brain is the major consumer of glucose, needing maybe 120 grams a day in people who aren’t yet on a low carb eating program. Low carb eating reduces the brain’s glucose requirements considerably, and those who are very low carb (VLC) and keto-adapted may only require about 30 grams of glucose per day to fuel the brain (and little-to-none to fuel the muscles at <75% max efforts). Twenty of those grams can come from glycerol (a byproduct of fat metabolism) and the balance from gluconeogenesis in the liver (which can actually make up to a whopping 150 grams a day if you haven’t metabolically damaged it with NAFLD through fructose overdosing). Bottom line, unless you are a physical laborer or are training (exercising) hard on a daily basis, once you become fat-adapted, you probably don’t ever need to consume more than 150 grams of dietary carbs – and you can probably thrive on far less. Many PBers do very well (including working out) on 30-70 grams a day.

The Fat Paradigm

The Fat Paradigm, under which the human species has thrived quite effectively for two and a half million years, recognizes that human metabolism is pre-programmed by evolution to be primarily fat-based (the real preferred fuel). In other words, our genes expect us to function optimally when we consume fats and can easily access our stored fat. The Fat Paradigm acknowledges that the body is able to manufacture adequate glucose as needed. It acknowledges that most typical human movement patterns can be fueled almost entirely by fats and/or ketones (PDF) if need be, but can draw on glycogen when energy bursts are required (and which can then be replaced over time). It acknowledges that fat (and cholesterol) are not the proximate cause of heart disease. It acknowledges that fat cells are designed to release stored fatty acids as required, especially during times of scarcity or fasting. It allows for intermittent fasting as a means of accelerating fat loss without sacrificing muscle tissue. It increases insulin sensitivity, modulates energy and mood swings, and allows for a normal and healthy drop in hunger and cravings. There is a downside, however: you can’t train long and hard day-in and day-out in the fat paradigm.

Now then, having explained all this, please understand that I am not carb phobic. I actually permit more carbs in the Primal Blueprint than many other low carb eating strategies. I prefer to view carbs as the “elective” macronutrient, as a tool to use to manipulate your glycogen levels as needed. Low carb isn’t even the main objective of eating in the PB: eliminating grains, sugars and seed oils are the primary objective. Of course, when you get rid of that crap and naturally limit your carb intake to veggies, root tubers and a few fruits, you almost invariably decrease carbs to under 150 grams a day. And that emulates our ancestral dietary intake.

I came up with a simple Carbohydrate Curve a few years ago that offers a pretty concise picture of where most people ought to fall if they are seeking optimum health and energy, depending on their size, weight, sex, age, goals, etc. Now, many hundreds of thousands of user experiences later, I am finding that the Curve is pretty much spot on for a large segment of the population.

When I say generally that a chronic intake of over 150 grams of carbs can lead to insidious weight gain over a lifetime, I am factoring in the concept that many people are at the effect of a familial genetic predisposition to storing fat easily under the carb paradigm (the 60+% overweight). I am also factoring in the drop in metabolism that happens naturally with age, as well as the fact that PBers don’t NEED to purge and refill glycogen stores every day via exercise. Yes, there are some people (a small percentage of outliers) who might maintain pretty decent body composition at up to 300 grams a day on little exercise. I would bet that they also are selective about the carb sources and do a better job of controlling overall calories, so there’s little excess to store. For most of the population, that 150 mark remains a good average level for maintaining ideal body composition.

Well, that was a lot to digest today. You see where I’m going with this. I need your help in showing the health community that their basic assumptions are wrong and that they need to make a Metabolic Paradigm Shift. I’m sure there will be lots of specific questions, so bring  ‘em on and I’ll do a follow up post in a week or two.

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. JAMA. 2003 Apr 9;289(14):1837-50.

    Efficacy and safety of low-carbohydrate diets: a systematic review.


    We performed MEDLINE and bibliographic searches for English-language studies published between January 1, 1966, and February 15, 2003, with key words such as low carbohydrate, ketogenic, and diet.


    There is insufficient evidence to make recommendations for or against the use of low-carbohydrate diets, particularly among participants older than age 50 years, for use longer than 90 days, or for diets of 20 g/d or less of carbohydrates. Among the published studies, participant weight loss while using low-carbohydrate diets was principally associated with decreased caloric intake and increased diet duration but not with reduced carbohydrate content.

    Seth wrote on June 1st, 2011
    • “There is insufficient evidence to make recommendations for or against the use of low-carbohydrate diets”

      Yup. One of the fundamental laws of real science is that if you refuse to ask the right questions, the answers you get are meaningless. Even if they are correct. What passes for science in the field of nutrition is mostly superstition. Low-carb diets are simply NOT STUDIED, or if they are, it is invariably using partially hydrogenated corn oil as the main source of fat (e.g.

      OTOH, I have yet to see a study in which dietary carbohydrate was reduced, even slightly, that did not produce health improvements. Although said improvements are *ALWAYS* attributed to something other than the carbohydrate reduction.

      Howard wrote on June 1st, 2011
    • OK Seth,

      Lot’s to consider from your posts:


      “I can understand why one would believe this to be evidence for preferential use of fat by the body. However, it’s misleading. The reason animals have evolved to store calories in the form of fat is because adipose (fat) contains very little water compared to stores of glucose (glycogen). For every gram of glycogen, there’s something on the order of 3-4 grams of water with it. We evolved to store energy as fat simply because it’s a very efficient calorie storage mechanism….I don’t think it’s accurate to say that energy is stored as fat because the body prefers to utilize fat….”

      I was kinda hoping you would take this approach to defend the lack of glycogen storage due to water storage requirements AND energy efficiency. This observation on your part allows evolutionary pressures (my thing remember) to come into their own.

      AGREED – you cannot conclusively state that “that energy is stored as fat because the body prefers to utilize fat”, however that does not mean you cannot hypothesise the following:

      What you have just stated is that the organism (i.e. animals including humans) prefers fat storage due to the fact that carbs require significantly more water to be stored with them AND fat is a more energy dense nutrient.

      So, why do you assume that evolution works in only ONE direction? By the VERY fact that carb storage is inefficient and cumbersome due to water storage needs, this would provide SELECTION pressures for the organism (ALL of them) to FAVOUR fatty acid metabolism.

      Due to the fact that you SO ELOQUENTLY and emphatically NAIL the final nail in the coffin for carbs as an energy source – i.e. they SUCK as an energy for storage for an living organism, then the organisms that developed EFFICIENT metabolisms for the energy source that IS EASILY stored would prosper when food was scarce etc, which happened often before we humans worked out how to used OIL energy to counter nature (fertilisers, pesticides and intensive farming ALL rely on oil energy – without it, we cannot feed the population)

      You have just provided the VERY reason that fats are a preferred energy source, because over MILLIONS of years of evolution (even before we were humans) we (and all other animals) evolved with a selection pressure for efficient use of the energy source that is most EASILY stored – FATS

      NOW in anticipation of your (and probably others reading this) chomping at the bit for all the “VEGETARIAN” animals, I have the trump card for you.

      Let me quote from a great website I found on the subject (written by a PhD no less!!!):

      “No mammal — not even the herbivores — has developed an enzyme that will digest vegetable fibre. This is why we tend to discount it when calculating our calorie intakes. However, while mammals have not developed an enzyme that will digest fibre, there are lots of micro-organisms and bacteria that can the job for them. The herbivores employ billions of these bacteria.”

      “In a herbivore such as the gorilla, the caecum and colon harbour huge colonies of bacteria which ferment carbohydrates, particularly fibre, and use it to produce short chain fatty acids (SCFA) — principally acetic, proprionic and butyric acids. These are then absorbed into the body to be used as a source of energy.

      If we look at the gorilla’s diet, we now see that the authors of the study into the western lowland gorilla’s diet find that the fibre provides some 1.5 kcals of energy per gram of fibre, in the form of SCFA. As the fibre averages about three-fourths of the gorilla’s diet, this energy forms a highly significant proportion of the gorilla’s total energy intake.

      These SCFAs must be added to the fats already present in the gorilla’s diet, which gives us the following proportions:

      Overall energy
      (kcal) per 100g %age
      Protein 47.1 24.3%
      Available carbs 30.6 15.8%
      Fat 4.9 2.5%
      SCFA from fibre 111.0 57.7%

      This gives totals of:

      protein = 24.3%
      carbs = 15.8%
      fats = 59.8%

      In other words, although the western lowland gorilla’s diet, exclusively of leaves, looks like a very low-fat, carbohydrate-rich diet, it is actually a high-fat, moderate-protein, low-carb diet.”


      1. Popovich DG, et al. The Western Lowland Gorilla Diet Has Implications for the Health of Humans and Other Hominoids. J Nutr 1997; 127: 2000-2005.

      Ruminants do the same.

      Let that sink in… The fibre is fermented by intestinal bacteria to produce short chain FATTY acids (i.e. FATS). The kicker is these SCFA are also almost ALL saturated!!!

      This is found at the following web site:

      There are references for the article (about 8 or so I believe)

      Even those herbivores are running on fats (they just need a symbiotic relationship with some bacteria to make the fats from the otherwise nutritionally poor fibrous plants).

      Secondly you write:

      “I just can’t make an argument that the body prefers fat, mainly because the brain does not utilize fat. Most physiological processes in the body (e.g., cardiovascular, metabolic, etc.) function so as to serve the brain first.”

      This is not entirely true. The brain DOES utilise (sorry I’m Australian – I spell English, not American) fats, via the utilisation of Ketones… Sure it does not use a fatty acid, but the conversion of fats into ketones provides the brain with an energy source… and quite an effective one at that.

      However yet again you are making an ALL or NOTHING argument…WHY?! Why can’t the body prefer fats in general… again to remind you no one is saying eat NO CARBS.

      And even if you did, apart from ketone bodies, with sufficient protein in the diet (over what is needed to prevent use of muscle tissue) the utilisation of gluconeogenisis would provide enough glucose for the brain, and to your point about acetone… if you needed it constantly, with NO carbs, but consuming over 50, 100 or up to 150 in carbs a day would easily supply enough (approx 120) for your brain either alone or with some gluconeogenisis.

      I just do not get why you fall back into the assumption of NO carbs is what is being proposed? The ENTIRE premise here is that fats are a GREAT energy source for most of the body, and what carbs you do need for your brain is so low as to NOT require the consumption of carbs by eating grains of any sort.

      Also, the fact we thrived and survived as a species PRIOR to the consumption of grains, just PROVES a diet minimal in carbs is absolutely FINE, if not preferential.


      ““We found (range of medians in en%) intakes of moderate-to-high protein (25-29), moderate-to-high fat (30-39) and moderate carbohydrates (39-40).””

      Nice citation. A few things:

      1) I’m wary of these studies with HUGE ranges, especially if conducted be recent observations… unfortunately (for them) no tribe on this planet hasn’t had some external influence from our “science” and “knowledge”… Even the authors state: “The objective of the present study was to reconstruct multiple Paleolithic diets to estimate the ranges of nutrient intakes upon which humanity evolved.” Reconstruct is not observe.

      2) You left out a conclusion that was important enough to be in the abstract “We conclude that compared with Western diets, Paleolithic diets contained consistently higher protein and LCP, and lower LA. These are likely to contribute to the known beneficial effects of Paleolithic-like diets, e.g. through increased satiety/satiation. Disparities between Paleolithic, contemporary and recommended intakes might be important factors underlying the aetiology of common Western diseases. Data on Paleolithic diets and lifestyle, rather than the investigation of single nutrients, might be useful for the rational design of clinical trials”

      I love this, all people like, myself, Mark (and others like us) want is for the DOGMA of low fat is good, high fat is bad to be at least TESTED scientifically. As your initial reaction has demonstrated, the prejudice AGAINST this dietary approach is SO vehement that opponents even MISS crucial facts (like it isn’t NO CARB) and go on the attack. Again without any evidence, just feelings, they cannot get around the fact that the reason you see the brain running on glucose only, is because you have NEVER let your brain run without what is in evolutionary terms a VERY high level of blood glucose.

      I was going to ignore your human milk factoid, as it’s relevance to overall human nutrition is obvious. What human milk provides a human infant is hardly proof of anything other than what a human breast is capable of producing!!! Additionally, this nutrient analysis was almost CERTAINLY conducted on mothers that eat MOSTLY carbs due to the current nutritional DOGMA! Perhaps if they were fed a diet that was richer in fats and protein they milk would be nutritionally different?! We know that milks of ALL animals are a product of the food eaten by the animal producing them (hence the issue with drug consumption during breast feeding – almost ALL drugs get into breast milk)…

      However in the end your factoid provides an answer “1.1% protein, 4.2% fat, 7.0% lactose” SO YES the % of carbs is higher… but CALCULATE the energy provided by each nutrient then you get:

      Protein – 6.27% of the energy
      Carbs – 39.89% of the energy


      Fats – 53.85% of the energy

      Again, us pro fat anti carbers are not being as basic as saying if you eat 20 gms of carbs you need to eat at least 21 gms of fats – we are saying that the MAJORITY of your dietary energy should came from fats!!!

      And this leads to the next posts you had about nutrient profiles, but first:

      “(I also agree that a ketogenic diet my be healthy in some respects for the brain, based on some interesting research articles I read today).”

      WOW – amazing (and not unexpected from me)… care to share the citation for this article (like you have for others), so that other skeptics can read for themselves and perhaps have their own epiphany!? Once again, I have to say you are better than most, for being so open to finding out more… Perhaps all this typing on my part was worth it if you even take that nugget of “new” (it isn’t new) information to counter your indoctrination… sorry I mean education by the “academics” in nutrition and physiology.

      Anyway onwards:

      “the rest of the daily requirements just for resting metabolic function (1600 kcal, for example) would have to be made up in large proportion in fat and protein. 100 grams of carbohydrate is only 400 kcal. Healthy, daily activity would about double the required calorie intake. This paradigm (100-150 grams carbo) seems to be okay just to meet resting metabolic needs (or to lose weight), but remember that our primitive ancestors were also distance runners! There’s has to be room for calorie intake for physical activity.”

      Again a few things:

      1) True 100gms is only 400 kcals (and 150gms (Mark’s suggested upper limit) is 600 kcals). However consider how the primitive man would get even 100 gms of carbs. You have already acknowledged that primitive humans did not eat wheat, rice or corn (we couldn’t as they are toxic until processed and then cooked). They mostly ate leafy plants and fruits… I trust you still agree.

      Well lets just do the math as they say.

      You can look this up yourself, but the carb content per 100gms for almost ALL leafy plants ranges between 1g – about 5gms, with an average of 3gms (I haven’t found higher, in checking spinach, lettuce, cucumber (technically the fruit), celery, etc but there may be). Let’s be generous and say that for some reason plants have LESS carbs than they had in the past (unlikely as humans have actively SELECTED for increased sweetness in ALL domesticated plants).. and even add 50% to the TOP figure that so we say (artificially mind you) that ALL vegetable matter that humans eat has about 7.5 gms of carbs per 100gms (i.e. 7.5%). And let’s assume that when it isn’t season for fruit that you can only get carbs from vegetable matter – fair assumption I believe?

      So to get 100gms of carbs (JUST 400 kcals as you point out), you would have to eat 100/7.5% = 1333.33 gms – or 1.33 KILOGRAMS (2.93 POUNDS) of vegetables!!!

      Mind you this would be RAW until we were able to cook!

      For 150gms (600kcals) = 2kgs (4.4 lbs) I call BULLSHIT!!! There is no way our primitive ancestors were chewing 2kg/4.4lbs of raw vegetables every day… what’s worse if we take the ACTUAL average 3% carbs the figures are mind blowing, with 5kgs/11lbs for a measly 150gms of carbohydrate!!!! NO WAY, they would spend all day eating… let alone the rest squatting to excrete all the undigestible fibre.

      Now let’s say they did have fruit during the seasons. And let’s take bananas, because they are some of the HIGHEST % carbs of any fruit.

      A banana has 22.8 gms of carbs per 100 gms – or 22.8% (data from Now taking this as the % carbs for ancient man (which it WASN’T bananas are THE food that has consistently been artificially selected by man to add more sweetness, wild bananas are borderline sweet – but i’ll concede it for this comparison, as I cannot know what the ancient carb composition of bananas was, even if I’m near certain it was less) and then doing the same calculation:

      150 gms (600 kcals) of carbs would require 150/22.8% = 657.89 gms (1.45lbs) of banana. According to that roughly equates to nearly 4.5 “EXTRA large (9″ or longer)” bananas!!! There is NO way we were walking around finding that many LARGE bananas each and EVERY day – let ALONE more than that.

      2) “remember that our primitive ancestors were also distance runners! There’s has to be room for calorie intake for physical activity”

      I am confident about this (as I have done my own research into this subject) and I even contributed to one of Mark’s posts last year, after which he asked me for the reference, and then wrote his own piece summarising the data. The original post Mark wrote is here:

      My comments (as Luke in Oz (Oz being Australia)) pointed out research by Dr. Daniel Lieberman. It also included the excellent youtube link that shows that we walk/jogged/sprinted/walked when we hunted (not an all out run):

      On that tip about the Lieberman research Mark looked into it and wrote this post:

      Between both those you will see we were NOT the long distance runners that some want us to believe we are. We mostly walked and tracked, with some jogging and sprinting as well.

      ALSO – not EVERYONE in the tribe hunted (although an interesting factoid is that the females also hunted at times). The hunting party was a select group (no doubt chosen for their skills), and as the victors of the hunt, no doubt go to choose the select animal parts to eat. aLso interesting is that it has been shown that hunter-gatherer tribes that have dogs to assist with the hunt or in their camps do NOT feed the dogs the organs, offal and fatty cuts, they eat these preferentially (due to nutritional value) and throw the dogs the LEAN cuts of meat.

      So these members of the tribe definitely had high energy expenditure on days of the hunt and were fed accordingly with PROTEIN and FATS.

      However it is well documented they did NOT hunt every day. After a long hunt like the one in the video they would REST for at least a day (if not more). Additionally many studies have demonstrated that hunter gatherer cultures were NOT in constant search for food and that they had significant leisure time, especially compared to us rat-race modern humans.

      Again let’s do some maths:

      25yo – 5’11” (180cm) male, weighing about 158.7lbs (72kgs) (BMI of 22.2 – which would be typical for a hunter-gatherer, I trust you agree). I picked 25, as it is a fact that hunting and tracking is NOT an easy skill, and the lead hunters were at least this age if not older (the Lieberman study shows the age was about 35).

      Basal metabolic rate = 1789 kcals

      Based on the data from Lieberman of average of about 6km/h (~4mph) for about 4 hours average (which is about right, as the typical distance was 35kms (~22 miles), then from I calculate the energy expenditure as 2,885 kcals

      Meaning that day the expended ~ 4674 kcals – massive huh!?

      Yet, next few days they rest (one kudu or wilder beast yields ~ 120kgs (265lbs) of edible mass – so even for a tribe of 20 that provides 6kgs (13lbs) of meat per person – which is enough for DAYS without another hunt (humans learnt to dry meat for preservation) very early), basically lounge around to recover, so lets say compared to BMR, they burn ~2,200 kcals.

      Although without refrigeration they tended to FEAST up big on the meat and fat from the hunt on the night of the hunt and morning after the hunt and then just eat the gathered nuts, seeds, leafy plants and fruits in the days between. They also could fast for some time if needed.

      Anyway lets say one day hunt then 3 days off, total energy over 4 days is 2819 kcals average per day.

      With 6kgs of meat and nuts and seeds and leafy vegetables, this is not hard to fulfil. Also note that non-hunters needed far less, as they didn’t have that spike.

      Now let’s say from the average of 2800 kcals they did consume half of their carbs from vegetables, and the other half from bananas (which would be a rare luxury – but hey I’ll give it to you, EVEN at the artificially HIGH 5 carbs per 100 gms of 7.5%). To JUST meet your requirement of at LESST 150gm of carbs per days suggests:

      600kcals from the carbs in leafy stuff and fruits (1kg leafy stuff AND 2 bananas EVERY day)

      That leaves 2200 kcals

      Lets say a typical human just cannot eat more than about 200gms of protein a day without feeling stupidly full (anyone that tries to eat that much protein a day usually can’t because the ability of protein to make you feel full means they just can’t shove any more in their mouths!!)

      Assuming ~25% protein per 100gms (typical for most meats that are not LEAN), then this means they eat about 800gms of meat to get another 800kcals

      Leaving 1400 kcals for fats… fats are the ONLY way they could get the rest of their energy.

      At 9kcals per gram, they would need to consume about 156 gms of fats (~1404 kcals) to get to the daily requirement.

      THEY HAVE TO EAT fats (from the animal, nuts, seeds – wherever), because if the even ate JUST half that amount of fat to give only 700 kcals per day from fats, they then need to make up the other 700kcals from carbs or protein.

      With both being 4kcals per g – that means another 700/4 = 175 gms of carbs or protein or a combination of both. Lets split it down the middle at 87.5gms for carbs and 87.5 for protein.

      Thats another ~600gms (1.3lbs) of leafy stuff PLUS ANOTHER banana to make up the 87.5 gms for carbs and another 175 gms of meat… REALLY!?

      If you want to argue their energy expenditure was higher, then you just make it even HARDER for carbs to be the energy source!!!

      The most efficient way for ancient humans to get their energy requirements for each day was to eat FATS – PERIOD. Without grains (that give ~ 50-80% per 100 gms carbs) at their disposal, then the only way to get all that energy, without spending your WHOLE day chewing and crapping was to eat FATS.

      If you look at the available carbs in the foods they could get, the only choice was to eat more fat, otherwise they would starve. There is no way they ate kilograms of green stuff, and so many bananas (when if at all they were available)… without grains they HAD to eat fats and protein, and this is why the human body MUST run fine on fats and protein with a few carbs.

      Now for your quote from a paper:

      ““Our macronutrient projections for worldwide hunter-gatherer diets indicate that these diets would be extremely high in protein (19–35% of energy) and low in carbohydrate (22–40% of energy) by normal Western standards, whereas the fat intake would be comparable or higher (28–58% of energy) than values currently consumed in modern, industrialized societies.””

      1) This looks like observations of current hunter-gather tribes. These tribes have cooking, so they can now eat tubers and more starchy vegetables.

      Now I know we can cook, but for at least 75% of the existence of homo sapiens we did not have cooking, so our biochemical pathways are skewed towards not eating starchy vegetables.

      Additionally even when we did learn to cook, we only started FARMING about 10,000 tears ago… prior to that finding a tuber or starchy vegetable was not as easy as grabbing a bag of spuds from the grocer!!! So again, whilst they no doubt ate and very much enjoyed those bags of carbs when they found them, you could not assume they ate these regularly, let alone every day!!!

      2) By the way, taking the low end of 22% carbs (come one I have given you so many overestimates above), then 600 kcals, if 22% of daily intake = a total intake of ~2730 kcals per day… up near where the hunters above would need… and WAY lower than the 200-300 gns of carbs in the western diet (300gms of carbs with a 50% – 80% carb content per 100 gms is NOT a lot of rice, pasta, bread, corn etc, it is near IMPOSSIBLE to get to eating leafy vegetables and some fruit (unless you make that fruit a juice)


      We performed MEDLINE and bibliographic searches for English-language studies published between January 1, 1966, and February 15, 2003, with key words such as low carbohydrate, ketogenic, and diet.


      There is insufficient evidence to make recommendations for or against the use of low-carbohydrate diets, particularly among participants older than age 50 years, for use longer than 90 days, or for diets of 20 g/d or less of carbohydrates. Among the published studies, participant weight loss while using low-carbohydrate diets was principally associated with decreased caloric intake and increased diet duration but not with reduced carbohydrate content.”

      OK this one gets me slightly peeved…

      You have studies from 1996 – 2003…

      The whole fat is bad, carbs are good hypothesis (Ancel Keys is the “scientist” responsible for this whole mess) started in the 70’s… after that the US government decided to issue food pyramids based on Key’s flawed data.

      After that almost all studies were conducted from the assumption that low carb (and hence higher fat/protein) were bad. In double blinded studies this sort of bias could still influence the interpretation of the results, because whilst the measurements were blinded, the analysis and reporting is not.

      In DIET studies that by definition CANNOT be blinded (people know what they eat, and researchers know what they are eating), the possibilities for bias are HUGE.

      This is what I like to use the logic of the maths of above combined with the knowledge of what people did eat – you can’t just say – oh well, Palaeolithic man must have been eating rice – we KNOW this is not true. We know what they had available both prior to cooking and after, but prior to agriculture and eating grains. Using the KNOWN nutritional values of these foods, we can determine whether eating 2-5kgs of leaves for 600 kcals makes sense!!!

      The other issue is design… the type of fat used can skew results, particularly if in an attempt to reduce variables (i.e. bias), the participant is fed some sort of “food goo” that is made up of either fat, protein or carbs… this approach is often results in bias towards carbs, as sweet stuff is alway more palatable than protein goo and fat goo (especially COLD fat goo).

      Additionally, often the diet studies do cross overs, with LESS than the 2-4 weeks that is recognised for the human body to get off the carb addiction and firing efficiently on the fat burning mode – hence AGAIN they bias the results, as often the participants will feel fatigued and drop out – like ALL addictions, slowly removing carbs and weening off is the approach to reduce withdrawal symptoms – although cold turkey gives the best results if you can get through the initial stages!!! 😉

      Finally (for this one) the conclusions do NOT mean low carb diets are NOT the best nutritional approach – they just mean these studies, with all the possible flaws in design they would likely have, cannot say they are good OR bad… so what?! At a minimum this conclusion means that low fat/higher carb diets are the SAME (as this would have been the comparison diet!!!)… so if there isn’t enough to say low carb isn’t good or bad, then the SAME can be said of the comparison.

      Finally, look at one of the criteria for the “particularly” exception – less than 20g/d of carbs!!!

      WHERE on this site, and WHEN has ANYONE suggested less than 20g/day (OK on a fast day you get less than 20g/day, but you also get ZERO fats and proteins!!!)… the recommendation is 50-100 for weight loss “sweet spot” and 100-150 for maintenance… this is WAY above this criteria!!!

      I do note your statement that you are more in agreement with all of this now… although I noticed all these citations and statements, which suggests you are still holding out.

      I REALLY do hope you don’t mind me bashing out these monster replies, but each point is worth addressing, and hopefully you WILL keep looking into this.

      Trust me, as I said I came from the most CONVENTIONAL WISDOM of industries (Big Pharma), and I was skeptical at first… However the science DOES support this approach, but it means going beyond nutrition science and drawing on evolution, biochemistry, anthropology, history, politics (BIG PART of the nutrition policy debacle) and economics (lets face it – if we never jumped onto cheap nasty carbs, probably AT LEAST 50% of the human population wouldn’t even exist – removing grains from your diet (particularly corn and soy products) means 80% of what is in a supermarket is now inedible!!!). Lastly you need to apply natural skepticism to “official” views and have the ability to apply some logic (as above – 5kgs of leave PER day – not likely!!!)

      When you taking a broader multidisciplinary view to the question, the answer is ALWAYS the same – the human body (and that of all animals once you include the fatty acids created the symbiotic bacteria in herbivore intestines) runs optimally on a diet predominately consisting of fats, protein and a FEW carbs.

      This is how Charles Darwin came up with evolution by natural selection. He was not stuck in one view of the world through the eyes of biology, he also recognised and understood geology and geological time (which immediately gave him more than 6000 years, he understood environments and climates and recognised ecological niches, which allowed him to recognise the similarity of “role” that certain animals had in many different countries and ecosystems (an apex predator, the small mammals, rodents, birds, ruminants, each with a similar evolutionary niche in their environment. And finally he was a keen observer and was willing to discard what he thought he knew about the world and was taught about how all the animals and plants came into being. He also had the ability to use logic to look at seemingly different data and see that one thing lead to another and it was consistent with what was observed… This is why he is the GREATEST scientist that existed… he literally changed our understanding about EVERYTHING… what is more, what he proposed was before the explosion in fossil discovery, and then DNA, both of which reinforce his insight into how things evolved on this planet… Was he 100% right – NO, but he was a damned side more correct than the official view of the world.

      So I can only encourage you to look beyond nutrition journals (all your citations are from nutrition journals) and read some journals in the other areas I mentioned above, and even more areas if it adds to the knowledge of this area. Also, don’t just read journals… read books and blogs and websites (they are NOT all intellectually lacking – granted most are)…

      Anyway, I rarely post here, and usually I have my say and then leave everyone else to have their say for a good 3-6 months (check in every 2nd day and read 1-2 articles a week though), so I will leave this MONSTER post as my last for now.

      Good luck with your exploration of this topic, I know that like your views on ketones have shifted, the more you look, the more you will realise that there is a better way for human nutrition… the fact you are so qualified and discovering this now is brilliant, as it may mean as an insider you could change it all!!!

      Over and out!!!


      Luke wrote on June 2nd, 2011
      • Hey, I REALLY appreciate everything you wrote down here. That was an amazing summary. It really helped me connect the dots.

        George wrote on October 23rd, 2011
  2. I guess everybody sees what they look for, I see “there is insufficient evidence” as “there is not enough evidence yet”, others see it as “this is proof against it”.

    Oddly, I just posted another study, done by the Heart and Vascular Institute of the Johns Hopkins University School of Medicine and its conclusions were predominately in favor of a LCHF diet. Of course they had to throw in the meaningless phrase, “healthy fats”, but at this point, such is to be expected.

    Bill DeWitt wrote on June 1st, 2011
  3. Actually, reviewing how that study was done, the phrase should be read, “We were unable to find sufficient evidence”… the evidence is there, you just have to know how to look for it.

    Bill DeWitt wrote on June 1st, 2011
    • Not unable. I would bet money the more accurate word would be “unwilling.”

      Howard wrote on June 1st, 2011
  4. Just ran across this, thought it might be of interest here –

    “The athlete with more efficient fat conversion moves at a faster pace when fat is the main energy source. In the 1989 Hawaii Ironman Mark Allen ran a 2:40 marathon (the fastest recorded in the event) following 5:30 of hard effort. No human has enough carbs left on board to sustain such intensity for 8 hours. In a state of carbohydrate-depletion, his rate of work in the marathon depended on an ability to oxidize fat at a rate of 1.15g/minute, which is roughly 50% higher than most national-class athletes can achieve. An average level of fat oxidation (.76g/minute) would have produced a much lower rate of work and a time for the marathon of 3:30.”

    Bill DeWitt wrote on June 9th, 2011
  5. OK, It held my previous post for moderation because of the link, but here’s the quote (below). I’m thinking about doing a 200 mile hike while fasting to see if it can be done. I’m pretty fully keto-adapted to moderate exercise, and have fasted for 3 and 5 day periods while walking 3-4 miles a day. If I get a break in my classes, it might make a good experiment.

    “The athlete with more efficient fat conversion moves at a faster pace when fat is the main energy source. In the 1989 Hawaii Ironman Mark Allen ran a 2:40 marathon (the fastest recorded in the event) following 5:30 of hard effort. No human has enough carbs left on board to sustain such intensity for 8 hours. In a state of carbohydrate-depletion, his rate of work in the marathon depended on an ability to oxidize fat at a rate of 1.15g/minute, which is roughly 50% higher than most national-class athletes can achieve. An average level of fat oxidation (.76g/minute) would have produced a much lower rate of work and a time for the marathon of 3:30.”

    Bill DeWitt wrote on June 9th, 2011
    • Athletes consume carbohydrate during these types of races. Mark Allen consumed carbohydrate during this race. They are not carboydrate-depleted.

      Seth wrote on June 12th, 2011
      • Well then, there you go. No need to even think about this anymore, we have our answer, since “Athletes consume carbohydrates during these types of races” and Mark Allen is an athlete in once of these types of races, presto facto, he clearly ate carbohydrates during this race, which proves that all atheletes are not carb depleted during these types of races, because they all eat carbs… A perfect circle of logic, defended from all sides, preventing the need to ever learn anything we don’t already know. Thanks Seth! And BTW, your links to that were fascinating!

        Bill DeWitt wrote on June 12th, 2011
  6. Thanks Bill Dewitt….for the post about Mark Allen in the ’89 IRON MAN run…
    Take that …Mr. “bag of cornstarch”…
    LOL GROK ON>>>

    Daveman wrote on June 9th, 2011
  7. Excuse my ignorance, but what’s an HEDer.


    Rizsa wrote on June 11th, 2011
  8. Why does the myth that the more you exercise (read, athletic), the more carbs you need to fuel energy?

    In exercise, as in daily activity, protein converts to glycogen in the absence of carbohydrates.

    I have cycled (mountain biked) up the Andes (now this was day in day out for over 17 days) and many similar terrains. I have run 10km+ fun runs and run around 8km at least 4-5 times per week and neither I or my performance has suffered. In fact most people are astonished that I can perform at the level that I do on “low-carb”.

    I have also lived and traveled extensively in Asia. Westerners assume Asians eat rice in the same quantities that we do when we frequent an Asian restaurant.

    They do not. The Japanese would eat a finger bowl of rice and then leave some in the bowl. The Chinese would eat a finger bowl of rice. The Indians eat the most rice. Asians do not pile their (large) bowls up, Mt Vesuvius high and then order second and third servings of rice to “mop up the sauce”. In an authentic chinese restaurant (in the US, UK), the waiting staff are often surprised when tables order more rice than served initially.

    Finally as to comments that carbohydrates are older than “civilisation itself” – this is true. Carbohydrates were probably on this earth before primates even got to the trees.

    However, man eating carbohydrates is not as old as civilisation itself (other than in PB quantities). Man only began harvesting wheat and grains 7k or 20k (Im sorry, I forget which) years ago!.

    Finally addressing the same posters comments – if we only ate the amount of carbs that our grandparents did, we’d all be fine. The copious consumption of carbs at every meal and even as meal substitutes is a very modern day phenomena (about 50 years and getting worse each subsequent decade).

    Epigenetics aside, it takes much much longer than that for evolutionary changes to occur. We will not see the evolutionary changes required for some 100,000+ years.

    Keep up the good work Mark.

    A fantastic site.

    ps I have been low-carbing/PB’g for 11 years now!

    Buzzy2010 wrote on June 12th, 2011
  9. Anecdotes are indeed poor evidence Seth, but not nearly as poor as imaginary, untested, hypothetical situations which are asserted to work out in favor of your point of view. Mark provided his working definition of the term “prefer” and someone choosing a different definition and using that as an argument is a classical fallacy, which your education should name for you.

    Bill DeWitt wrote on June 18th, 2011
  10. none of you clowns can reproduce evolution purposefully in a laboratory but it all happened by accident in some swamp somewhere…sure glad those fruit trees crawled out of the oceans and planted themselves and the bees elovled themselves to pollinate them

    brad johnson wrote on June 23rd, 2011
  11. Great Post! I missed this post on my own personal holiday. Something about May 19th that always comes up for me.

    bradley wrote on July 11th, 2011
  12. Nutrition has always interested me, but I’m one of the “outliers” in the graph, being that I have always been classified as underweight. I would love to gain weight (lean muscle, of course) but nothing has worked so far.

    Considering the common weight concerns in the nation right now, many people look at me with a mix of jealousy/envy/anger if I mention that I would like to put on a few more pounds to hide my skeleton. I feel like it is accepted as OK to be looking to lose weight, but arrogant, or even insulting, to be looking to gain weight. Let’s just say, not many people understand my situation.

    I’m 33, male, 6ft, 152 lbs. I’ve tried heavy weight lifting, protein shakes, raw eggs, etc, etc, but nothing seems to work.

    Just curious as to what the PB diet could offer to me. I’ve always planned to live till 100+( original plan was to be on Mars, but, oh well), but just now getting serious about that joke. :-)

    Any advice on healthy weight gain diets, or longevity in general? I’ve also seen studies related to fasting and longevity, and would love to hear thoughts on that.

    An underweight (yes, we are out there) nutrition hobbyist.

    Brandon wrote on July 25th, 2011
  13. So why does fruit taste soooo amazing then? And why am I not at all fat with a high fruit diet. I do have lots of energy.

    Saying all carbs are the same is like saying all fats are the same.

    Nick wrote on August 30th, 2011
  14. Hi,

    I understand all of this, but what if my goal is to gain weight and build muscle?

    I’m in my early 20s and began the paleo diet in 2008. I just recently stopped a few weeks ago because I wasn’t seeing any muscle growth and felt weak in the gym. I now eat rice before working out and have the energy to lift heavy. Prior to the paleo diet, I was a bread addicted teen and always ate low-fat. I was 130 and 5’8 (more muscular). When I went paleo, I went down to 120 (lost muscle, no energy, but no acne!). I tried increasing fat while on paleo, but still had little energy to lift.

    Am I just better suited to eating more carbs?

    `will wrote on September 14th, 2011
    • If you lost weight beyond excess fat, you probably weren’t getting enough calories. The paleo diet has far less variety than a carb heavy diet, and just requires a change of habit. Utilize fat sources, such as olive oil, coconut products, and seeds to boost your calories intake.

      Takes a bit getting used to when we are used to eating a bit of meat with a huge serving of mash potatoes or rice. Or whipping up some beans, or cranking out a huge bowl of cereal just for the heck of it. Or downing an entire pizza.

      Remember, lean mean isn’t that calories heavy. 4oz of lean chicken only has like 110 calories. So a plate of chicken and vegetables might be anywhere between 200-300 calories. You’d have to eat 6+ meals of that to get enough calories if you were lifting. Again, I think it’s all about utilizing fat sources.

      George wrote on October 23rd, 2011
  15. I remember when I was doing “Body For Life”, and after 5 weeks I got so frustrated that it was not working, I called the 1-800 number and they told me that the people who succeed on the program i.e., the ones who win the $$ are the “genetically gifted” types that Mark posted about above. Wow! What a scam! I was working out 6 days a weel and following the diet to a “t” with no results.

    KingdomWarrioress wrote on September 20th, 2011
  16. Hi Mark,

    What happens to a dietary fat that was not used as energy? Say due to an individual’s inactivity.


    Vlad wrote on September 21st, 2011
  17. I found the answer. “Excess fatty acids, glucose, and other nutrients can be stored efficiently as fat” from wiki

    Vlad wrote on September 23rd, 2011
  18. To the skinny ones, I’m skinny fat too due to fructose malabsorption (otherwise I’d probably just be fat!). Try picking low fodmap vegies and getting enough omega 3s and protein, as well as less omega 6s and more sat and mono fats. I’m just trying this now, after researching fats and then finding this site. Make sure you get heaps of vegies, there’s not much carbs in them.9 cups a day is probably ideal according to Dr Wahls.

    emily wrote on October 17th, 2011
  19. Is there a grain free bread?

    Is gluten free bread acceptable?

    Jon wrote on December 4th, 2011
  20. Don’t mind the theory, but have some issue. Especially when comparing these concepts to the diet of “primitive” man.

    A) There is no real evidence of what early man actually ate, but what we DO know points to not only meats but a diet high in sugars from fruits/vegetables, and actually rather LOW in fat since wild game, fish, and birds tend to be very lean. Saturated fats would be on the low end, most being poly/monounsaturated from nuts.

    B) If carbs impact longevity and health, please examine and explain far east culture. The Japanese are among those with the longest life spans, and leanest physiques on the planet. Their diet is RICH in rice products, and vegetable starches.

    C) The leanest and most healthy athletes are among fitness models, bodybuilders, runners, etc., all of which recommend high-carb diets. The reason they recommend them isn’t because they’ve been “brainwashed” by society – but because fat simply doesn’t deliver high-impact energy, and they see it first hand when they train. The only thing these athletes say about low-carb, is that you get thin, like for contest prep (and thin does NOT=healthy).

    I could understand this for a sedentary person, someone who doesn’t want to exercise and wants to become “thin,” where thin=healthy in their minds, but for a high performance athlete, there’s no way – those are very rare cases for a reason.

    Sorry, I’m going to go with what all 99.99% of the world’s elite athletes, and healthiest, active (present day) cultures do. Eat carbs.

    But good luck everyone!!

    Skeptic wrote on December 4th, 2011
    • well said bro! 100% true for me!

      Kalin wrote on April 10th, 2012
    • The elite athletes MUST eat lots of carbs because they have so little bodyfat and they train HARD. Fat truly IS the preferred fuel for exercise and resting levels below 50-60%VO2max. Even a slightly elevated heart rate above the resting heartrate still burns 90+% FAT and only 10% glucose. But endurance athletes train at levels much beyond the body’s ability to continue to provide free fatty acids to the muscles to be oxidized (burned). Their bodies flip from aerobic to ANaerobic and the fat:glucose used ratio decreases, i.e. they MUST eat carbs to continue performing at this level or they HIT THE WALL. THAT is why they “recommend” high-carb diets. But if you are not as active, this many carbs (read: CALORIES) will make you FAT, period. These athletes also eat 3000-5000+ calories a day. Are you going to do that too and remain a non-active adult? You’re reading too much into their “advice” and CLEARLY do not know the WHOLE story lol.

      Eric wrote on January 27th, 2013

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