• Your life and health are your own responsibility.
• Your decisions to act (or not act) based on information or advice anyone provides you—including me—are your own responsibility.


Carbohydrates Matter, At Least At The Low End (There Is No Such Thing As A “Calorie” To Your Body, Part VII)

Caution: contains SCIENCE!

In previous installments, we’ve proven the following:

  • A calorie is not a calorie when you eat it at a different time of day.
  • A calorie is not a calorie when you eat it in a differently processed form.
  • A calorie is not a calorie when you eat it as a wholly different food.
  • A calorie is not a calorie when you eat it as protein, instead of carbohydrate or fat.
  • A calorie is not a calorie when you change the type of fat, or when you substitute it for sugar.
  • Controlled weight-loss studies do not produce results consistent with “calorie math”.
  • Even if all calories were equal (and we’ve proven they’re not), the errors in estimating our true “calorie” intake exceed the changes calculated by the 3500-calorie rule (“calorie math”) by approximately two orders of magnitude.

(This is a multi-part series. Return to Part I, Part II, Part III, Part IV, Part V, or Part VI.)

Empirical Evidence: A Calorie Is Not A Calorie When You Add Carbohydrate To A Zero-Carb Diet

There are many anecdotal reports of people finding it difficult or impossible to gain weight on a zero-carb diet, even with massive overfeeding. Yet there are controlled trials that seem to show high-fat diets having no such overfeeding advantage. Why not?

This study provides some clues:

J Nutr Biochem. 2003 Jan;14(1):32-9.
Effects of dietary carbohydrate on the development of obesity in heterozygous Zucker rats.
Morris KL, Namey TC, Zemel MB.

“…We fed 6-week old male heterozygous (fa/+) lean rats carbohydrate-free diets containing primarily saturated fat either ad libitum or pair-fed. These diets were compared to standard chow and to a high saturated fat mixed diet containing 10% energy from sucrose for 4 weeks.”

This is a good start: many “high-fat” diet trials use industrial lard containing ~20% linoleic acid (an omega-6 fat), or industrial seed oils with even greater LA content—which, as we’ve seen in the previous installment, is strongly implicated in the development of obesity. Furthermore, most “high-fat” laboratory diets contain about 20% purified sugar…which, as we’ve previously noted, seems to be obesogenic by itself.

A Short Digression: “High-Fat” Almost Always Means High Sugar

The results of Morris 2003 call into question all obesity research featuring “high-fat diets”. First, they’re usually on a strain of mice (C57BL/6, or “black six”) specifically selected for its propensity to quickly become obese when fed high-fat diets, unlike other strains of mice (let alone other animals, like humans, that aren’t natural seed-eating herbivores). More importantly, in nearly every case, they use D12492—a mix of purified ingredients containing no actual food, and specifically designed to make C57BL/6 mice obese as quickly as possible. (More here, via Dr. Chris Masterjohn)

D12492 contains 20% purified sugars.

So be skeptical whenever you see a headline claiming negative effects for “high-fat diets”.

All diets were standardized to 20% protein and 11% corn oil. (Yes, these are industrial Frankendiets.) The carbohydrate-free diet contained 69% coconut oil; the 10% sucrose diet contained 59% coconut oil and 10% sucrose (table sugar), with no other carbohydrate; and the “standard chow” diet contained 59% cornstarch and no coconut oil.

Does that matter? 10% carbohydrate is still VLC, right? That’s only 50 carbs on a 2000-calorie diet…and it’s still almost 60% coconut oil, so they should be mostly in ketosis, right?

Here’s what happened after four weeks. First, the food intake figures, from Table 2:

Table 2

The zero-carb rats ate 36% more “calories” than the chow rats, and about the same (3% more) as the 10% sucrose rats…and the pair-fed zero-carb rats ate the same number of “calories” as the 70% carb (“standard chow”) rats. (That’s what “pair-fed” means: one group is fed only as much as another group eats.) So if the CICO zealots are correct (IT’S PHYSICS!!!1!!1), the standard chow and pair-fed rats ought to be lean, while the zero-carb and 10% carb rats ought to be obese.

Meanwhile, back in reality, here’s what happened:

Figure 1A

Grams of fat gained during the 4-week feeding period, by diet.

“Weight gain was negligible in the carbohydrate free groups compared to standard diet and 10% sucrose diet (p = 0.03). This was reflected in energy efficiency which was markedly reduced (90%) in the carbohydrate-free groups compared to the other groups (p = 0.04).”
“Animals consuming the standard or mixed (10 en% sucrose) diets gained 90% more weight (p = 0.03) than animals consuming the carbohydrate-free diet ad libitum (Fig. 1A).” -Ibid.

The data is presented confusingly, so I’ll put it all together in table form.

There are a couple problems with the data presentation in this paper. First, the “feed efficiency” graph doesn’t appear to agree with the primary data they present, so I’ve used the values from Table 2 and Figure 1A to recalculate it. Second, the paper doesn’t give the actual weight of the rats, just the change in weight…but given the typical developmental schedule of a heterozygous Zucker rat, it’s likely between 200g and 400g.

Dietary group                  Dietary energy consumed
(1 kJ = ~4.2 dietary calories, or kcal)
% increase
in dietary energy
from baseline
% carbohydrate
in diet
Weight gain
per rat (g)
Weight gain
per megajoule
of energy consumed (g/MJ)
Standard (10% sucrose, 70% total carb) 22400 kJ 0% 70% 20 g 0.89
Zero-carbohydrate pair-fed 22700 kJ 1% 0% -1 g -0.04
10% sucrose, 10% total carb 29500 kJ 32% 10% 20 g 0.68
Zero-carbohydrate 30500 kJ 36% 0% 2 g 0.07

Let’s put these results in English:

  • The 10% sucrose rats ate 32% more food than the standard (70% carb) rats, but gained the same amount of weight (20g).
  • The zero-carb rats ate slightly more than the 10% sucrose rats, and 36% more than the standard rats—but gained an insignificant amount of weight (2g).
  • The pair-fed zero-carb rats ate the same amount as the standard rats (that’s what “pair-fed” means), but lost a negligible amount of weight (-1g).

Clearly, in this study, weight gain (and loss) doesn’t correspond at all to “calories” consumed! It corresponds more closely to the percentage of calories from carbohydrate—regardless of “calories”.

Conclusions: Carbohydrate Intake Matters (at least at the low end)

I’m reluctant to extrapolate directly from rats to humans—but these outcomes seem to correspond reasonably well to observed reality in humans.

  • A high-fat diet increased food intake—but the rats didn’t get fat, even on over 35% more “calories”, unless sugar was added.
  • Just 10% carbohydrate, from sugar, was enough to make a non-fattening zero-carb diet strongly fattening.
  • Even at 10% carbohydrate from sugar, it still took 32% more “calories” to gain the same amount of weight that the rats gained on a 70% carbohydrate diet.
  • It appears that much of the advantage of zero-carb diets is gone at just 10% carbohydrate.
  • The studies I’ve seen that claim no advantage to varying macronutrient intakes don’t reduce carbohydrate to 10% or below. (Or they reduce energy intake to starvation levels, which is a whole another article in itself.)
  • As I’ve previously warned in this article, almost-ketosis is a bad place to live. You get the pain of trying to adapt to ketosis without ever fully adapting—and, apparently, you also lose most of the associated resistance to weight gain. Most “paleo fails” I see are from hanging around 10% carbs, usually while exercising heavily.

This series will continue! Meanwhile, you can read earlier chapters by going back to Part I, Part II, Part III, Part IV, Part V, or Part VI.

Live in freedom, live in beauty.


Did this article clarify your own thoughts and experiences? Great! Share it using the widget below, and leave a comment. Do you feel like arguing? Please save us all some time and read the other installments (linked above) before bringing up points we’ve already covered at length.

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Permalink: Carbohydrates Matter, At Least At The Low End (There Is No Such Thing As A “Calorie” To Your Body, Part VII)
  • Ash Simmonds

    Ah what a pleasure to find my own silly writings against CICO as your first reference. :D

    Pingback from AussieExotics…


  • François "Wizz&

    “It appears that much of the advantage of zero-carb diets is gone at just 10% carbohydrate.”

    I knew it! I was certain that there was some kind of treshold to trigger the real benefits of low-carbing. I’ve tried to convince a couple of friends who tried “low” carb and failed, but of course they wouldn’t listen.

    I guess this treshold must have variations from individual to individual. I know mine is extremely low, close to zero (metabolic resistance blues…).

    Would be interesting to have studies on humans rather than laboratory animals… probably won’t happen anytime soon.

  • pzo

    Must still be dark in the Sierra’s, eh? Barely light here on the bayou in Florida.

    Empiricism, dontcha love it? It’s like what Dr. Eades has posted recently with his TV interviews; how the lipid hypothesis folks keep failing at their experiments but refuse to accept the obvious: They are wrong.

    In my many decades on this planet, observing my fellow so-called “homo sapiens” I’ve concluded that we really should be “homo emotocus,” or something. We emote, we react, then we claim a rational basis for those emotions. A further condensation of human “thought” is repeating something often enough makes it true. Joseph Goebbels, propaganda minister for the Nazi’s, understood this. And right here in America, disgraced Vice President Spiro Agnew of later disgraced President Richard Nixon, use a phrase I still love: “Nattering nabobs (of negativism).”

    So much conversation, especially on Spacebook, Twatter (!!), and on forums is just that, nattering from intellectually vacuous nabobs. And it certainly includes many in the world of nutrition.

    Oh, back on topic. If true, this horribly complicates real world carb experiences. When I’ve tried to practice VLC, I felt “spacey” a lot and could not get any performance on my mountain bike (Yes, it’s Florida now but my Trek and I have also done Monarch Pass, Colorado) There was no evidence over a month or more that I would adjust. And I found the diet terribly boring.

    I’m at 57% fat, 21% protein and carbs, + a “lot” of wine or distilled spirits, 2000-2100 calories excluding ethyl alcohol, and my weight won’t consistently drop below 240 pounds (I’m 6’2″.) Four years ago, during my VLC days, drinking just as much, I did lose weight, eventually down to 210. But I was exercising more, too.

    Guess I’d lose weight doing VLC again, stop drinking, but then, life would be misery. No mun, no hun, no oral fun.

  • Sofie

    No, life is completely enjoyable without drinking. Change can be difficult, but don’t pretend your happiness depends on nerga.

  • Annlee

    I would love to see the carb better broken out, too – since sucrose is 50% each glucose and fructose. Would the sugar composition matter? I suspect the answer is “yes.”

  • Sherwood

    Interesting read. Wonder what the results would be if various long chain carbs were used instead?

    While testing on humans is clearly desireable, the next stage would be to replicate with pigs, which are metabolically even closer to people than rats are.

    It would appear that at low levels carbs are acting as a catylist, or are an essential starting material for some metabolic process. No carbs means that some process is blocked, and another process is used.

    What happens to the extra calories? Are the zero carb rats, despite the surplus of calories burning them — are they more active, have higher body temps? Or are they excreting them in their waste?

    In one sense CICO will be true. As you said it’s physics. If it appears otherwise, it means that the biological bookkeepers aren’t doing their job. Conservation of mass/energy and all that. Those calories are there somewhere.

    Measuring the metabolic activity of a rat would require different cages to trap and measure the CO2. Measuring the energy in the crap would be fairly easy. Dry it, and do the calorimeter thing.

  • Paul Lee

    From my own experiences I agree with this. I’ve lost wait rapidly on low carb but it tends to stall after a while (though this might be carbs creeping back in). Begs the question of how to loose weight on high carb without starvation/fasting or spending hours on a treadmill. For example I know Indonesians who are wafer thin, yet seem to exist on several rice meals a day with a little fish etc.. If you are largely an inactive coach potato then zero/vlc will be the only way to go

  • MargaretRC

    That explains nicely why my husband was able to lose a fair amount of fat when he went very low carb and exercised a lot, but gained it all back as soon as he reduced exercise and allowed a relatively small amount of carbs (mostly wheat, not sugar) back in. He still doesn’t eat near as many carbs as most or as he did before, yet has as much fat around his middle as he did before he ditched the wheat and sugar. And yes, he has all the indicators of being insulin resistant. Wish I could convince him that even the little bit of carbs he’s eating is affecting him, but he’s resistant to change. Loves his bread and pasta. :( I suspect the only thing that will bring about a change in attitude is if he is diagnosed as actually diabetic.

  • MargaretRC

    Thank you for this, by the way.

  • Paleobird

    This article should be brought to the attention of the “Sugar Bees” over at Mark’s Daily Apple. They are the ones nattering on about the gospel according to R@y P##t so loudly and so long that most of the dedicated low carbers have given up and gone elsewhere.

    You don’t win an argument by being the loudest and last one standing. You win it with actual scientific fact.

    Thanks JS

  • Chris Highcock

    What about the Calories Out side of the equation?

  • Jacquie

    I’m confused, sorry. Are you conflating sugar and carbs?? (I’m still on my healing quest, trying to make sense of how to lose weight and fix an ailing body.) Are you saying that more than 10% carbs from non-sugary/non-starchy sources is still going to be a problem??

  • Sean

    Reducing energy efficiency by relying on fat for metabolism can be really bad for your health, and your heart's ability to pump blood: “Alterations in cardiac energy metabolism can profoundly affect cardiac efficiency. Excessive use of FAs has been shown to be especially important, either by decreasing the efficiency of producing ATP, or by decreasing ATP availability for contractile function.” http://www.heartandmetabolism.com/download/53/8.pdf

    [This is wrong, but understandably so and in an interesting way…make sure read my reply several comments below -JS]

  • Renaud

    Did they measure fat going strait to poop ?
    Did they mesure physical activity ?
    AFAIK rats grows for about 12 weeks (experiment started at 6)… so, do we observe healthy stabilisation of weight or stunted growth ?

  • Sean

    Renaud, great points there about growth vs stunted growth.

  • Johnnyv

    Interesting although as you say rats a very different to humans.
    If only there were some more metabolic ward studies with decent dietary compositions.

  • con

    This confirms my experience,
    I lost 95 lbs. no exercise at all, on a zero carb diet. When I added in a cup of fruit weight loss stopped. I maintain this loss without much effort by eating high fat, moderate protein and one carb daily ie. 1 salad, 2 c. kefir,1 fruit etc. Occasionally(1x month) a high carb chocolate bar, burrito or other fabulous favorite.

    Boring? not hardly! It represents freedom from obesity.

  • con

    This confirms my experience,
    I lost 95 lbs. no exercise at all, on a zero carb diet. When I added in a cup of fruit weight loss stopped. I maintain this loss without much effort by eating high fat, moderate protein and one carb daily ie. 1 salad, 2 c. kefir,1 fruit etc. Occasionally(1x month) a high carb chocolate bar, burrito or other fabulous favorite.

    Boring? not hardly! It represents freedom from obesity.

  • BawdyWench

    I’m with Jacqui. Is this total carbs, or just the sugar part of the carbs? For example, if the total carbs of a food total 13 grams, but the pure sugar carbs are only 5 grams, do you count the 13 grams or the 5 grams?

    As Jacqui said, “Are you saying that more than 10% carbs from non-sugary/non-starchy sources is still going to be a problem??”

    Can someone respond, please?

  • Jacquie

    Hmm- just to clarify, I was talking about the effect of real whole food and whether you are now saying that veges are also a problem? I’m trying to figure out how this paper might reflect on the ‘eat like a predator” page here.
    Thanks JS, this is my go-to blog for making sense of this stuff, but I feel like I’m missing something this time

  • Ash:

    While the plural of “anecdote” is not “fact”, there exists enough anecdotal evidence that I felt it necessary to keep an open mind.



    “I was certain that there was some kind of treshold to trigger the real benefits of low-carbing. … I guess this treshold must have variations from individual to individual.”

    I believe you're correct…and I'll be exploring metabolic individuality in detail in future installments.



    Much of what passes for “nutrition information” is just provocation marketing.  Make bold claims that YOUR CURRENT DIET IS KILLING YOU!!11!, throw in a couple half-assed scientific references to an obscure biochemical pathway with no real-world relevance, and you too can sell a $39.95 e-book.

    That said, my purpose here is not to advocate low-carb for everyone: I'm not even low-carb myself!  I'm suggesting that, based on the evidence, “mostly-sorta-low-carb” is a bad place to live: you're getting most of the negatives without most of the benefits.  Result: either go keto or don't.

    Also, it's not clear that alcohol has the same effect as sugar or maltodextrin: see, for instance, this study.

    Yes, going keto will leave you with a much smaller glycolytic reserve for sprinting, on a bike or anywhere else.  You have to decide for yourself if that's worth it.  And “feeling spacey” is keto-adaptation: again, being “mostly-sorta-low-carb” generally stops you from keto-adapting.



    I'm not ready to dismiss fine liquor as nerga, but I take your point.  We all have to decide what's most important to us.  Relevant: “Just Say It,” Jim Steel.



    I suspect it'll matter, but I'm not sure by how much.  My guess is that it's is likely to be an insulin-mediated response and fructose doesn't stimulate insulin secretion, so other carbs would be at least as bad or worse — but I'm not going to invest much in that hypothesis.

    Frankly, a combination of measurement error and metabolic individuality means you'll most likely have to experiment on your own anyway.



    “Wonder what the results would be if various long chain carbs were used instead?”

    As I said above to Anniee, I suspect they won't be much different unless they're so long as to have a meaningfully lower GI.  However, if they're so long that they're soluble fiber (i.e. indigestible except by colon bacteria) instead of carbohydrate, they probably won't have the same fattening effect.

    “It would appear that at low levels carbs are acting as a catylist, or are an essential starting material for some metabolic process. No carbs means that some process is blocked, and another process is used.  What happens to the extra calories?”

    I agree.  One guess would be peroxisomal oxidation, which would waste much of the energy as heat, but I don't know. 

    Note that some of the studies in previous installments measured fecal losses, oxygen consumption, etc…unfortunately, this one did not.


    More soon!


  • neal matheson

    Hi J
    “I’m not even low-carb myself!” What would be your definition of low-carb?
    I think I would fall into the “mostly sorta lowcarb” space I eat a small amount of carbohydrates in fruit and starch mostly every day.

  • Paul Lee:

    “Begs the question of how to loose weight on high carb without starvation/fasting or spending hours on a treadmill.”

    1. Restore metabolic flexibility if possible, through a combination of moderate exercise over time

    2. Pay close attention to nutrient density, as hunger is primarily nutrient-driven and it's easy to consume lots of empty starch

    “If you are largely an inactive coach potato then zero/vlc will be the only way to go”

    I think that's usually true: if you're not fortunate enough to be naturally skinny, and you're not willing to exercise to keep your met flex, you'll probably need to force your RQ down with VLC/ZC.



    “That explains nicely why my husband was able to lose a fair amount of fat when he went very low carb and exercised a lot, but gained it all back as soon as he reduced exercise and allowed a relatively small amount of carbs (mostly wheat, not sugar) back in.”

    That's a double whammy: he lost the advantage of VLC, and he probably lost some met flex due to no longer exercising.  Maybe even a triple whammy, given how sensitive some people are to gluten.

    I'm glad you find my work valuable!



    P*atarians are remarkably resistant to the introduction of facts.  If you want a laugh, read this and note the lack of response.


    Chris Highcock:

    As I noted above, this experiment doesn't tell us where the extra energy went — though other experiments measured it, or attempted to (e.g. Part VI). 

    We know it didn't vanish, because physics is true — but that's not helpful.  Analogy: If my toilet overflows, it's not helpful to say “Your problem is obvious: more water is entering your toilet than leaving it.”  We're only interested in how to get more water to leave the toilet, and “how?” is a much more pressing question than “why?”

    Therein lies the difference between physics and the naive application of CICO.  Physics says “In a closed system, energy is neither created nor destroyed.”  CICO says “Calories out has a direct linear relationship to exercise, calories in (as approximated by Wilbur Atwater based on the average of a series of empirical measurements in the 1800s), and nothing else.


    First, optimum health and fat loss are not exactly the same goal.  They're usually congruent — but I view fat loss as a consequence of good health.  If your body is functioning properly and well-nourished, it should be happy to let go of some fat stores — whether VLC or not.

    That being said, not everyone has good metabolic flexibility, or can restore it quickly via exercise (there's a study I can't find now showing that people who became T2D at an early age did not restore met flex with exercise, unlike people who became T2D later on), in which case VLC can help.

    Moving on to the type of carb: I don't think we can know, based on this experiment, whether it's only the refined sugar, or whether other carbs have the same effect at 10%.  If I had to guess, I'd say what I said above to Anniee: any sugary or starchy carb will have the same effect.  Exception: green veggies that aren't sugary/starchy root veggies (onions, carrots, potatoes), whose few carbs tend to be mostly theoretical and used in digestion.  (I tend to agree with Paul Jaminet that veggie carbs don't count.)

    That being said, it's something you have to experiment with on your own, because my thoughts on a rat study don't trump your own direct experience.

    Finally, let me be clear: the point of this article is not that everyone should eat VLC or zero-carb!  (I don't prescribe a specific carb intake in “Eat Like A Predator” beyond “don't eat lots more carbohydrate than you need to.”)  The message I'm hoping to communicate is this: stay out of the no-man's-land between 5% and 15% carbs.  (Higher if you're very physically active, and carbs from green veggies don't count.)

    Does this help?


    More soon!


  • neal matheson

    To elaborate, it is unlikely that I would be able to eat (or afford) a ketogenic diet due to well, basically I don’t want eat seperately from my family.

  • Renaud

    Hi J,

    I’m with you about this no man’s land between 5-15% (and also about things like CKD). I just think this study is nowhere near convincing.

  • Paul Lee

    My own experience of keto like diets is that appetite diminishes markedly which offsets their costs a little, which perhaps ties in JS’s feeling that hunger is indicative of deficiency of some sort. My own theory is that some extent humans are fativores and crave fat. After all if you don’t eat, that is what the body provides you with from your own store! But I agree bags of rice and potatoes are cheap, and tempting!

  • Dave

    Thanks for another great article! You reiterated a point I first read on Peter’s Hyperlipid blog: clinical rodent studies on ‘high fat’ diets are also high sugar diets. So, are we really testing the effect of dietary fat in isolation? Apparently not.

    Though fat loss is no longer a concern for me, I have seen benefits from continuing to eat low carb in conjunction with intermittent fasting. For one, fasting is easy. Secondly, I ride my bicycle to and from work. At the start of my low carb lifestyle nearly two years ago, I did notice a drop in strength on climbing hills. I think I’ve since regained my metabolic flexibility. Now, at my ‘most fasted’ part of the day, riding my bike uphill to get home, I’ve got energy I never knew I had before.

  • Sean:

    You're misunderstanding the paper you quote, which is understandable: Lopaschuk tends to overrepresent his search for a drug to help CHD patients as a quest for heart health in general.

    It's an interesting scientific detour, though, so I'll explain what's going on.

    First, anyone who has read a basic biochemistry textbook will know that “Fatty acids are the heart's main source of fuel, although ketone bodies as well as lactate can serve as fuel for heart muscle. In fact, heart muscle consumes acetoacetate in preference to glucose.” (Biochemistry, 5th edition, section 30.2)

    Why might this be the case?

    “Unlike skeletal muscle, heart muscle functions almost exclusively aerobically, as evidenced by the density of mitochondria in heart muscle. Moreover, the heart has virtually no glycogen reserves.” (Ibid.)

    Therefore, a heart running on fat is not an accident, nor a sign of sickness!  The heart is very specifically designed to run completely on fat. 

    This is not just true of humans: it is true of all known animals.  (At least the ones with hearts.)  This means that hundreds of millions of years of evolution have selected all known animals for the ability to run their hearts completely on fat.

    This is no surprise.  The liver's glycogen reserves (200-400 kcal) are rounding error compared to the body's fat reserves (typically over 100,000 kcal) — and since a stopped heart results in death in very short order, it's absolutely necessary that the heart have a consistent supply of energy.  (Also, fat-burning is “cleaner” than glucose-burning, but that's a whole another digression in itself.)

    Furthermore, the heart cannot ever “go anaerobic”, because a state in which the heart cannot deliver the necessary amount of oxygen because it's recovering from anaerobic exertion would be fatal within minutes.

    So: why would the Lopaschuk paper imply that running on fat is bad?

    “Efficiency” is a loaded word in everyday talk, but in the Lopaschuk paper, it's used with one very specific meaning: production of energy per unit of oxygen.  The paper explains at length why glucose metabolism is more “efficient” than fat metabolism — in the single, very specific sense of using less oxygen per ATP generated.

    Of course, in everyday reality, oxygen efficiency is not important at all to the heart — because the lungs and bloodstream can deliver far more oxygen than it's possible to use.  For normal people, the limitation on oxygen delivery is the amount of blood that the heart itself can pump.  See, for instance, Bassett 2000: “…The increase in VO2max with training results primarily from an increase in maximal cardiac output (not an increase in the a-v O2 difference).”  This is a limitation of the heart's strength and endurance, not its oxygen supply — and it only occurs when exercising at maximal intensity! 

    Thus, we can see that “oxygen efficiency” of the heart muscle is a red herring: it seems like it ought to be important, but it isn't.

    With one single exception: Lopaschuk's primary area of research is attempting to find drug therapies for heart disease patients.  In CHD, the heart is unable to supply itself with enough blood to provide the oxygen it requires, due to narrowed arteries.  Therefore, causing the heart to switch to glucose as a fuel can provide a temporary reprieve, since glucose is more “oxygen-efficient” than fat.

    This could be a life-extending therapy if he ever discovers a way to do it (though not a permanent solution: it'll keep people alive until they can get heart surgery) and I don't mean to minimize it — but Lopaschuk appears to dramatically overrepresent his quest for oxygen efficiency as a general health measure, when both biochemistry and evolutionary biology tells us this is wrong at the most basic level.

    I hope this helps!


  • Renaud, Sean:

    As I said above to Sherwood, we don't know where the extra energy went.  Re: your second question, I see no evidence that growth was stunted by the zero-carb diet.

    1. Zucker rats are sexually mature at six weeks.

    2. Note the abstract: “The subscapular and epididymal fat pats were increased 42% and 44%, respectively, in animals consuming the 10% sucrose diet compared to all other groups.”

    3. We don't have figures for total weight…but a mature non-fatty Zucker rat weighs perhaps 400g, and the rats gained 20g in four weeks, so weight gain during the four-week experiment (20g) was perhaps 5%.  Even if they were half adult size, we're still talking about a difference between 10% weight gain on the most fattening lab chow possible and zero weight gain. 

    A 5-10% difference doesn't qualify as “stunted”.



    No, rats aren't human — but they're much more like humans than mice are, being naturally omnivorous, so I take rat studies more seriously than mouse studies.  (Exception: fatty Zucker rats, and anything else bred to be obese.)

    The only human study I'm familiar with that features similarly extreme dietary compositions is Keckwick and Pawan 1956 — which comes to similar conclusions, though I'm reluctant to rely on it because it was so short.  (Note that the “refutation” of Keckwick and Pawan (Hood 1970) only ran for eight days, therefore featuring exactly the same problem.)

    People like to cite one and disparage the other, depending on their preconceived bias, but the only difference I see is that Keckwick and Pawan were honest about the real-world problems of getting people to stick to an extreme diet, even when they're hospital inpatients.  (Therefore, Keckwick and Pawan is a “metabolic ward” study, because all that means is the subjects slept in a hospital.  It's no guarantee they didn't cheat: there's plenty of food in hospitals.)



    That's why I wrote this article: it seems to jibe with many people's observed experience.

    Congratulations on losing 95# and keeping it off!  Statistically, almost no one does that without gastric bypass.


    BawdyWench, Jacquie:

    See my reply above to Jacquie.


    neal matheson:

    I'm certainly “low-carb” compared to average consumption and the nutrition guidelines — but I don't make any effort to restrict my intake beyond eating like a predator and not cheating too often, so I don't feel comfortable calling myself “low-carb”.

    Again, I'm not recommending that you go ketogenic…I'm just cautioning about ending up in “kinda-sorta-low-carb” by accident.  Fortunately, dietary experiments are easy to do, and inexpensive compared to medical intervention!



    “I just think this study is nowhere near convincing.”

    Convincing of what?


    Paul Lee:

    In general, I believe the effects of food on hunger are more important than their differing “caloric” value…but I already wrote that series of articles.



    I remember the first time I ate nothing all morning or for lunch, rode my bicycle in the afternoon, and made it back without feeling like I was going to starve or faint…it was wonderful!  I think the best part of regaining metabolic flexibility is the freedom from having to eat every few hours.

    One advantage of fasted training is that it increases your basal rate of fat oxidation, so you're less dependent on glucose.  I'm glad it's working for you!


    I'm finally caught up!  Thanks, everyone, for bringing an interesting discussion to the table.


  • Michelle T

    Hmmm … very interesting study. I don’t eat many carbs because I can’t digest bread and pasta, but this is definitely something worth sharing. I will admit that I am a calorie counter, though :/

  • Michelle T:

    As I've said before, I think most of the benefit of calorie counting comes from the simple act of keeping a food log, regardless of calories: it's easy for junk to sneak back into our diets, and keeping track of what we eat is often enough to cause us to cut down our consumption of junk.

    That being said, there can be a place for calorie counting once you've determined a roughly optimal diet and are simply trying to figure out how much of your preferred foods to eat. Otherwise, you're not just comparing apples to oranges — you're comparing them to coconut cream, potatoes, broccoli, and prime rib!


  • js290


    re: efficiency

    Per carbon atom, fatty acids supplies more ATP, and RER is lower. This would indicate fat uses less oxygen. Also from Cahill’s Fuel Metabolism in Starvation:

    β-HYDROXYBUTYRATE: THE MOST EFFICIENT FUEL Veech and colleagues discovered that administering β-hydroxybutyrate to the perfused rat heart in place of glucose increased work output but decreased oxygen consumption (35).

    (35) Control of glucose utilization in working perfused rat heart.

    re: CICO

    The other fundamental problem with CICO is it incorrectly treats CI and CO independently. In the reality of the coupled system that is metabolism, CI and CO affects each other.

  • js290:

    You are correct that fat uses less oxygen per ATP generated — but glucose contains much more oxygen than fat does (remember: C6-H12-O6 vs. long chains of carbon and hydrogen attached to one glycerol), so the net result is that more exogenous oxygen is required to oxidize fat.

    This short letter neatly sums up the situation: “…Each gram of palmitate produces significantly more high-energy bonds than a gram of glucose, and the caloric value of the stored high-energy phosphate bonds derived from the oxidation of a gram of palmitate is 2.4 times greater than that derived from a gram of glucose, albeit at a greater relative cost in oxygen. Hence, when oxygen is abundant and food is scarce, there is an advantage in utilizing fatty acids for fuel as opposed to using glucose. The reverse, however, would occur when food is plentiful and oxygen is scarce.

    Result: fat should be the preferred and most efficient fuel any time we are not pushing the limits of our aerobic capacity (“oxygen is scarce”). 

    And, in fact, this is how animal bodies work.


  • Howard

    @Sophie: “No, life is completely enjoyable without drinking.”

    I had to read that twice before I noticed the comma. ;)

    Back in college, I had plenty of opportunity to observe people who considered it fun to get drunk. I tried it. Exactly once. The experience was excruciatingly bad. To this day, I’m utterly bewildered as to why anyone would do that more than once. I conclude that enjoyability of life without drinking may depend heavily on both genetics and epigenetics, since my experience with that differed substantially from that of most of the others I have observed.

    BTW, I have also experienced morphine (legally, routinely used as a pre-op sedative in Navy hospitals back when I was in the Navy). I also wonder why anybody would want a second hit of that stuff, too. It was awful.

    There is one drug that I have experienced about which I completely understand the addiction potential. A Navy doctor sprayed some mist up my nose before examining my sinuses, and within a few seconds, I could tell it was the most powerful decongestant I had ever experienced. I also felt 10 feet tall and bulletproof. *Everything* was suddenly better. I asked him what the hell that was, and he replied that it was 0.5% cocaine in distilled water. Which really scared me. I know for certain sure that I really need to avoid that stuff, because if I ever got started, it would kill me. I would not be able to stop.


    @JS: “Congratulations on losing 95# and keeping it off! Statistically, almost no one does that without gastric bypass.”

    I lost a little over 100 lbs, and have kept it off for 13 years now (no gastric bypass) using a grain-free low-carb diet, with about a 15 lb fluctuation. Only problem is that I needed to lose 150 lbs, and that last 50 lbs is proving to be truly stubborn. I may need to try Jimmy’s nutritional ketosis experiment. Or, since those keto strips are prohibitively expensive, I may need to just go below 10% carb (I generally stay around 35-40g/day), and cut the protein back a bit (which I started a couple of weeks ago, but haven’t since any huge results yet).

    I’ve heard that you can actually make a living bragging about a 100 lb weight loss, but I think that folks looking at me would definitely notice that I’m still chubby, so I lack the credibility needed to pull that off. However, 50 lbs overweight beats 150+ lbs overweight.

  • Howard:

    Drug responses are strongly individual.  Some people, like yourself, find alcohol uninteresting, while others center their lives around obtaining it.  Others find cocaine uninteresting, while you find it strongly addictive.

    I'm sure this is because different drugs tickle different receptors and boost (or inhibit) different hormones and neurotransmitters — as do different dietary compositions.  I'll explore metabolic individuality in future installments.

    As far as “that last 50 pounds”, that's going to be very difficult, because you're strongly fighting leptin dynamics at that point — you don't get to 150# of extra fat without some adipocyte hyperplasia (more fat cells, not just bigger fat cells).  ItsTheWooo has posted at length about her usually-successful strategies for dealing with this.  Others find that reintroducing some amount of carb cycling helps…but at some point you may have to kill off some of those tiny shrunken non-leptin-producing fat cells, whether invasively (lipo) or non-invasively (cryolipolysis, lasers). 

    The good news is that none of this is necessary to be in good health: it's purely a cosmetic problem.


  • Johnnyv

    “that last 50 pounds”
    Better hope you were overeating butter and not soy or fish oil.

    Look at the difference in adipocyte number!
    I think I would write a different conclusion to the paper authors based on the data: “A diet low in polyunsaturated fat vs saturated and monounsaturated fat protects against adipocyte hyperplasia under conditions of overfeeding!”

    Essential fatty acids indeed but only in tiny quantities.

  • Johnnyv:

    That's a very interesting case of equal total weight and fat gain causing dramatically different metabolic effects...

    …and I'm sure similar situations contribute to the dramatic inter-individual variation in weight loss outcomes at the same “caloric deficit”.  Thank you for bringing it to my attention!


  • […] loss advantage if you stay really low-carb. It's from a mouse study, so take from it what you will: Carbohydrates Matter, At Least At The Low End (There Is No Such Thing As A “Calorie” To … If you do add carbs back in, post-workout is a good time to have them. Good sources are potatoes, […]

  • La Frite

    Hi J,

    Cool article. I just note that the study uses coconut oil, which is quite full of MCTs that are converted into ketone bodies. It would be nice to have a study as this one but using butter as well (far less MCT amount), and another rat group using say olive oil or something very low in PUFA anyway but very high in MUFA. I think that using coconut oil is a little biased towards ketone production. But on the other hand, just adding 10% of sucrose totally reverses the results. That’s amazing.

    For those who are LC dieters, just add resistant starch (30-40g / day) as described in details at freetheanimal.com


  • La Frite:

    Regarding your question, Romestaing 2007, from Part II, shows that coconut oil is indeed far less fattening per calorie than butter — but butter causes greater satiation and satiety, causing the rats to eat less of it.  (Butter is still less fattening per calorie than standard chow.) 

    The RS stuff is very interesting, but it's being oversold so hard (I've already encountered several straight-up misrepresentations of the scientific literature) that I don't take any of the hype at face value.  And vinegar has many of the same properties (e.g. improvements in blood glucose control — documented by scientific studies, not just uncontrolled n=1), plus it's an amazing topical AND internal antibacterial (SIBO? Drink vinegar, it'll be gone soon).  The main difference I see is that no one's driving the hype train for vinegar.  (PROTIP: acetic acid is the shortest SCFA.)


  • greensleeves

    “The RS stuff is very interesting, but it’s being oversold so hard (I’ve already encountered several straight-up misrepresentations of the scientific literature) that I don’t take any of the hype at face value.”

    Ty for that JS. The core issue here is that the world’s expert on fibers of all kinds, Dr. J Slavin of Minnesota, is happy to remark that different people digest different amounts of various fibers. There are people who do digest supposed “insoluble” fiber, depending on their microbiome, just as there are apparently people who can digest a large amount of that “resistant” starch.

    Notice that altho’ Slavin is the recognized expert, the starch proponents never cite her work at all. They just avoid the tower that is her research. Wonder why?

  • phd-er

    Hi JS! This is sorta off-topic but I’ve been a fan of your writings for a while and would be interested in your take on the following carb tale.

    I am struggling with high cholesterol and digestive issues and have been following a basically paleo / predator diet, with no grains or starches. (Rice and potatoes crash my digestion.) I gave up wheat a long time ago, too. BUT …

    I recently caught a virus and felt really sick. The only thing I wanted to eat in the world was saltine crackers and digestive biscuits. So I ate saltine crackers and digestive biscuits. And I felt great. My digestion handled these processed, gluten-loaded, trans-fatty (?) morsels of wheat like a dream. My energy rebounded, and right now I’m feeling tons better. What do you think is going on here???

  • greensleeves

    “What do you think is going on here???”

    I suggest that, like Melissa McEwen, you restricted yourself long enough to let yourself heal, and now you can perhaps experiment with a more WAPF-style diet in a careful way, if that interests you.

  • greensleeves:

    I'm not familar with Dr. Slavin's work, but I found and read her CV at your recommendation, and there's a lot there for me to investigate once I've covered my current subjects.  (That will take a while!)

    Remember, I said all the way back in mid-2012 that “Insulin, leptin, “food reward”, and the hypothalamus have all taken their turns: I predict gut flora will be the Next Big Thing.”  And here it is! 

    I further predict that most of the effects of RS will be due to its increase of serotonin production — which may be a good thing in the short term if you're dealing with insulin resistance and MetS, but which also explains many problems of the non-responders and negative-responders…and whose long-term effects may or may not be desirable, again depending on your individual metabolic history.


  • phd-er:

    1. If you've been avoiding starches, you're probably VLC.  Some people do better with some starches in their diet. To avoid the ones that give you trouble, try taking a tbsp of vinegar here and there, and follow the info from Norm Robillard's “Fast Tract Digestion” series (GERD/acid reflux, IBS/SIBO), which ranks foods according to their fermentation potential.  I know people having success with this protocol.

    2. As greensleeves said, the longer you've been paleo, the more your gut heals and the more tolerant you'll be towards gluten.  When I had only been paleo for a couple months, I cheated on pizza once and felt like I had been drugged: I walked around for an hour or so instead of driving straight home, because I didn't feel safe to drive!  Now I suffer only constipation and a bit of the non-specific blahs.

    That doesn't mean gluten is suddenly better for you…if you start cheating on a regular basis, you'll probably lose your tolerance again!  Again, check out Robillard's book for a guide to carbohydrates that should play nice with your gut.


  • greensleeves

    “I’m not familar with Dr. Slavin’s work, but I found and read her CV at your recommendation, and there’s a lot there for me to investigate once I’ve covered my current subjects.”

    Well good luck, JS. Slavin is apparently the expert on the gov’t food guidelines who dictated the fiber, grain & veggie parts. If you wanna attack those, wrestling with Slavin’s research will be inevitable.

  • greensleeves:

    I glanced through a couple recent papers and they seemed reasonable.  Of course, how they're represented, and how the government uses them to justify policy, are probably another matter entirely!


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