February 29, 2012

Nutritional Biochemistry

Do calories matter?

Read Time 9 minutes

In a word, yes.  But, technically this is the wrong question.

 The correct question is probably closer to, “What is the impact of the calories I consume on my body’s ability to store fat versus burn fat?

The immediate follow-up question to some variant of this first question is, “Should I be counting calories?” In a word, no. But you’ll want to read this post fully to qualify that answer.

Before I answer these important questions, let’s spend a few moments reviewing five key concepts.

Key concept #1 – the definition of a calorie

A calorie is a unit of measurement for energy content. By formal definition a calorie is the amount of heat energy required to raise one gram of water from 14.5 to 15.5 degrees Celsius at atmospheric pressure.  One-thousand calories is equal to 1 kilocalorie, or 1 kcal for short.    Here’s where it gets a bit tricky.  Most people use the term “kilocalorie” and “calorie” interchangeably.  So when someone says, “a gram of fat has 9 calories,” they actually mean 9 kcals.   The important thing to remember is that a calorie (or kcal) tells you how much energy you get by burning the food.  Literally.  In the “old days” this is how folks figured out the energy content of food using a device called a calorimeter.  In fact, to this day this is how caloric content is measured when doing very precise measurements of food intake for rigorous scientific studies.  As a general rule carbohydrates contain between 3 and 4 kcal per gram; proteins are about the same; fats contain approximately 9 kcal per gram.

[If you’re wondering why fats contain more heat energy than carbohydrates or proteins, it has to do with the number of high energy bonds they contain. Fats are primarily made up of carbon-hydrogen and carbon-carbon bonds, which have the most stored energy.  Carbs and proteins have these bonds also but “dilute” their heat energy with less energy-dense bonds involving oxygen and nitrogen.]


Key concept #2 – thermodynamics primer

It might be a good time, if you haven’t done so recently, to give a quick skim to my previous post, revisit the causality of obesity.  In this post I review, among other things, how the First Law of Thermodynamics explains fat accumulation and loss.  To reiterate, the First Law of Thermodynamics says that the change in energy of a closed system is equal to the energy entering the system less the energy leaving the system.  When we apply this to fat accumulation, it looks like this:


People like me (and others) get a bad rap from folks who lack the patience (or training, perhaps) to actually hear the entire argument through before throwing their hands in the air, waving them frantically, and screaming that we’re violating the First Law of Thermodynamics for asserting the Alternative Hypothesis (more on this below).

Let me be as crystal clear as possible, lest anyone feel the need to accuse me of suggesting the Earth is flat.  The First Law of Thermodynamics is not being violated by anything I am about to explain, including the Alternative Hypothesis.


Key concept #3 – current dogma

Conventional wisdom, perhaps better referred to as Current Dogma, says that you gain weight because you eat more than you expend.  This is almost true!  To be 100% true, it would read: when you gain weight, it is the case that you have necessarily eaten more than you expended.   Do you see the difference? It’s subtle but very important — arguably more important than any other sentence I will write.  The first statement says over-eating caused you to get fat. The second one says if you got fat, you overate, but the possibility remains that another factor led to you to overeat.

If you believe Current Dogma, of course you’ll believe that “calories count” and that counting them (and minimizing them) is the only way to lose weight.

Key concept #4 – the rub

Most folks — but not all — who subscribe to Current Dogma do so, in part, because they don’t appreciate one very important nuance.  In the equation above, explaining the First Law of Thermodynamics, they assume the variables on the right hand of the equal sign are INDEPENDENT variables.

Let me explain the difference between independent and dependent variables for those of you trying to suppress any memories you once had of eigenvectors.  As their names suggest, independent variables can change without affecting each other, while the opposite is true for dependent variables.  A few examples, however, are worth the time to make this easy to understand.

  • The weather and my mood are dependent variables.  When the weather goes from gloomy to sunny my mood tends to improve as a result of it, and vice versa (i.e., when the weather goes from sunny to gloomy, my mood goes from good to bad). In this case the dependence is only one-way, though; my mood changing has no impact on the weather.
  • My countenance and my interaction with people are dependent variables.  When I smile it seems to cause a more positive interaction with the people around me.  Similarly, when I’m having a good interaction with someone I tend to smile more.  In this case the dependence goes both ways.
  • My height (while I was still growing) and my hair length are independent variables.  Both of these variables can change without any impact on each other.

How does this tie into the idea of the First Law? Let’s re-write the First Law with a bit more specificity:

The change in our fat mass is equal to what we eat and drink (the only source of energy entering our system) less all of the energy we expend.


Now let’s be even more specific on the “expend” part of the equation.  We expend energy in four ways: Digestion (all the energy we require to break down food, plus the undigested portions that leave our body); Exercise (everyone knows what this is, but I tend to separate it from daily activity since people really like to focus on exercise); Daily activity (the non-exercise activity we carry out); Basal expenditure (the energy we expend “underlying” any activity – e.g., when you are resting).

Let me clarify something before going further.  There are several ways to enumerate and account for our energy expenditure. I happen to do it this way, but you can do it other ways.  The important thing is to make sure that you are collectively exhaustive when doing so (and mutually exclusive if you want to make your life easier – we call this MECE, pronounced “mee-see”).

The First Law is only valid when you consider ALL of the energy entering and leaving the system (i.e., your body).


Back to the independence versus dependence issue for a moment.  If you look at the equation above, and believe the red box has no impact on the green box, and vice versa, you are saying that energy input and energy expenditure are independent variables.  However, this is not the case, and that is exactly why this problem of energy balance is so vexing.  In fact, the figure below is a more accurate representation of what is actually going on (and even this is a gross oversimplification for reasons I will mention shortly).


What you eat actually changes how you expend energy.  Similarly, how you expend energy changes what (and how) you eat.  To be even more nuanced, what you eat further impacts what you subsequently eat.  As you increase (or decrease) in size, this impacts how you expend energy.

So there are actually a whole bunch of arrows all over this diagram (I’ve only shown 2: what you eat impacting how you expend, and vice versa. If I included all of the arrows, the diagram would get out of control pretty quickly).

I’m not telling you anything you don’t already know, even though it may sound like it for a moment.  When you exercise your appetite rises relative to when you don’t exercise.  When you eat a high carb meal you are more likely to eat again sooner compared to when you eat a high fat/protein meal due to less satiety.


Key concept #5 – the Alternative Hypothesis

If, like me, you don’t subscribe to Current Dogma, you’d better at least have an alternative hypothesis for how the world works.  Here it is:

Obesity is a growth disorder just like any other growth disorder.  Specifically, obesity is a disorder of excess fat accumulation.  Fat accumulation is determined not by the balance of calories consumed and expended but by the effect of specific nutrients on the hormonal regulation of fat metabolism.  Obesity is a condition where the body prioritizes the storage of fat rather than the utilization of fat.

Why is this different from Current DogmaCurrent Dogma says it doesn’t matter what you eat, it only matters how many calories that food contains.  If you eat more calories than you expend, you gain weight.  The last part is true, but the first part is not. The Alternative Hypothesis says it DOES matter what you eat and for reasons far beyond the stored heat energy in the food (i.e., the number of calories).

Let me use an example to illustrate this.  Consider the following table of various substances known to contain a lot of stored energy.  The table shows their energy content in units we usually use to describe energy density, kilojoules per gram (middle column), and I’ve converted to units we typically only use for food energy, kcal/g or “calories” per gram, (right column). [Here we need to be very clear to distinguish between a technical calorie and a kilocalorie, which is almost always what we mean.]  A kilojoule is about 240 calories (not kilocal), so 1 kj is about 0.24 kcal, and therefore 1 kj/g is about 0.24 kcal/g.

I’ve highlighted, in bold, four rows of things we typically eat: fat (olive oil, to be specific) with about 8.9 kcal/g; ethanol with about 7.0 kcal/g; starch with about 4.1 kcal/g; and protein with about 4.0 kcal/g.

I’ve also included in this table some other substances known to contain chemical energy such as liquid fuels (e.g., gasoline, diesel, jet fuel), coal, and gunpowder.  Hard to imagine a world without these chemicals, for sure.

A quick glance of the table, which I’ve ordered from top to bottom in terms of caloric density, would suggest eating olive oil would be more “fattening” than eating starch since it contains more calories per gram, assuming you subscribe to Current Dogma.

But that same logic would also suggest eating coal would be more fattening than starch and gunpowder less fattening than ethanol.   Gasoline would be more fattening than jet fuel.  Hmmmm.  Anyone interested in testing this hypothesis (personally)?  Despite my wildest self-experiments, this is one self-experiment I’ll pass on.  Why?  Well for the same reason you’d pass on it – you know that there are far more important consequences to drinking diesel or snorting gunpowder than their relative energy densities.


Sure, everything on this list is an organic molecule largely composed of the following four atoms: carbon, hydrogen, oxygen, and nitrogen.  Not to bore everyone with a lesson on organic chemistry, but it’s the actual bonds between these atoms that are responsible for their energy densities.  When you “liberate” (i.e., break) the bond between an atom of carbon and hydrogen, for example, you release an enormous amount of stored chemical energy.  This table tells you exactly how much energy you would release if you were to break the bonds in these molecules, but that’s all it tells you.  You can’t actually know, just by looking at this table, if jet fuel is more paraffinic than diesel or if gasoline has more isomerization than propane.  And, you certainly have no idea, from the information contained in this table, of exactly how each of these substances will impact the hormones, enzymes, and cell membranes in your body if you ingest them.

Is it relevant to our bodies that olive oil has about the same energy density (i.e., calories) as biodiesel (also known as fatty-acid methyl-ester)?  Or, is it more relevant to us that consuming olive oil has a very different effect on our bodies than consuming biodiesel beyond anything to do with the calories contained within them?  Obviously consuming equal caloric amounts of olive oil versus biodiesel will have a very different impact on our body.  Why then is it so hard to appreciate or accept that equal caloric values of olive oil and rice could also have very different impacts on our body?

The upshot

Let’s get back to the question you actually want to know the answer to.  Do calories “matter”, and should you be counting them?

Energy density (calories) of food does matter, for sure, but what matters much more is what that food does in and to our bodies.  Will the calories we consume create an environment in our bodies where we want to consume more energy than we expend?  Will the calories we consume create an environment in which our bodies prefer to store excess nutrients as fat rather than mobilize fat?  These are the choices we make every time we put something in our mouth.

Our bodies are complex and dynamic systems with more feedback loops than even the most elaborate Tianhe-1A computer.  This means that two people can eat the exact same things and do the exact same amount of exercise and yet store different amounts of fat.  Does it mean they have violated the First Law of Thermodynamics?  Of course not.

Similarly, genetically identical twins can eat different macronutrient diets (i.e., differing amounts of fat, protein, carbohydrates) of the same number of calories, while doing a constant amount of exercise, and accumulate different amounts of fat.  Does this violate the First Law of Thermodynamics?  Nope.

What you eat (along with other factors, like your genetic makeup, of course) impacts how your body partitions and stores fat.  In case anyone is wondering how I got over 2,000 words into this post without mentioning the i-word, wonder no longer.  Insulin, while not the only factor involved in this process, is probably at the top of the list. When you eat foods that have the double whammy of increasing insulin levels AND increasing your cell’s resistance to insulin, your body prioritizes fat storage over fat utilization.  No one disputes that insulin is the most singularly important hormone for causing fat cells to accumulate fat.  Somehow the dispute centers on what causes people (full of billions of fat cells) to accumulate fat.

All calories are not created equally:  The energy content of food (calories) matters, but it is less important than the metabolic effect of food on our body.

Photo by Aaron Barnaby on Unsplash

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  1. Superb article! And as an international instructor of Applied Physics, I fully approve of its content.
    Thank you, Peter!
    P.S. I’ve been following this wisdom for 16 months and am living proof that it is true.

    • Steve, thank you for your endorsement! Hopefully anyone thinking I’m suggesting the First Law doesn’t matter will read this. Good luck with your journey.

  2. Dear Dr. Attia,

    Thank you for this website. As I’m sure many of your readers here do, I try to read a lot of the different LC/Paleo/Primal/health blogs on a daily basis. And many times I’m left shaking my head or concerned I may be making less than optimal choices.

    Can you address the issue of developing insulin resistance on a low carb or VLC diet? I thought I fixed that by going LC. Now I’m reading it may lead to IR and/or Thyroid issues.

    Having gone LC a little over a year ago, I’ve both trained and competed while in Ketosis with no impact on performance. FWIW, I compete in a power related sport, all anaerobic. What I’m reading doesn’t jibe with my personal experience, but then again I’m only a year in, maybe it’s too soon to see a problem.

    PS – If I’ve missed it on another post my apologies, but where can a person donate to this site?

    • Michael, I do plan to write about the thyroid issue, but frankly I do not know the answer right now. I do know, however, that in humans, insulin resistance is absolutely reversed (i.e., we get more insulin sensitive) with a reduction in carbohydrates.

      • HIgh Peter,

        I’ve also seen this claim in numerous places. The idea is that, once your metabolism has switch to burning fat for fuel, you become peripherally insulin resistant, meaning your muscles and some other tissues will become insulin resistant in an effort to preserve glucose for your brain. If you then eat a big load of carbs, it takes longer for your muscles to decide to burn all of the suddenly available sugar, leading to elevated blood sugar. Of course, your body will quickly resume burning glucose after a few carb heavy meals, so it’s a short term phenomenon quite distinct from the insulin resistance caused by metabolic damage.

        • Yes, I have heard of this very transient issue, though, I’ve seen many cases to counter it (take a look at my OGTT pre- and post- low-carb): https://eatingacademy.com/how-low-carb-diet-reduced-my-risk-of-heart-disease
          After carb-restriction (though not yet ketotic), my glucose response was much better. So, like many things, I suspect this is highly dependent on many factors and probably tough to overly generalize.
          I still maintain that carb-restriction does not produce the same “variant” of IR that forms the cornerstone of metabolic syndrome, even when this transient issue is present.

      • Pete, are you saying when we go low carb, then eat carbohydrates, our insulin spikes to a higher level than if we were to just be eating a “normal” western diet to begin with? Maybe I’m confusing resistance and sensitivity?

        And, by this article are you saying that we CAN eat too much fat on a LC diet? In other words, x grams of fat (which may be different for everyone) = too many calories no matter how low carb you are, therefore you won’t lose fat? I know you agree that we can eat too much protein, as you’ve said over 150 grams of protein is too much (still waiting on the blog that explains that one 🙂 and can slow down or stall weight loss because that protein is just converted into glucose (or carbs I think). In other words, you believe that if 2 people were on low carb diets (both under 20g per day), but one ate too many grams of protein (200 for the sake of argument), and the other ate too many grams of fat (some arbitrary number that I won’t pretend to know), that neither would be able to lose weight because they either ate too many calories, or too much protein that was then converted to act like a carb by the body?

        Sorry, just trying to wrap my head around this because I’ve always thought Gary wrote and believed you basically can’t eat too many calories as long as you eat LC. You’ll either just not store them as fat, or you’ll be so full you just won’t be able to consume enough to gain fat?

        Looking forward to your response.

        • IR means the cells need more insulin than they would “normally” need to process glucose. When you reduce carbohydrates you experience lower levels of insulin basally (at rest), which has been shown repeatedly — especially in people who are insulin resistant — to reduce IR (which is the same as increasing insulin sensitivity). This is why virtually all Type 2 diabetics can stop using exogenous insulin with months (in some cases weeks) of eliminating carbs.
          What I am saying here is that if you CAN overdo it. Your body wants to be in a state of equilibrium. What that equilibrium is depends on what you eat. I used to weigh 200 pounds eating about 3,200 kcal/day. Today I weight 170 pounds eating about 4,500 kcal/day. Probably less exercise, too. So I have a new equilibrium based on a change in my “inputs.” If I ate 10,000 kcal/day for a month (even if still ketotic), I *do* believe my body would figure out a way to dispose of some of that excess, but not all of it. I’m just interested in doing that experiment as I don’t think I could force that much food down.

        • I’m responding to Peter’s response to Gary. I’ve been eating low-carb for a few months, and have found that my weight still fluctuates. When I ate a lot of nuts – 5-6 ounces – I’d gain. Perhaps I should try extremely low carb, and a tremendous amount of fat – but, I’m a little scared of that – and it seems a bit unappealing. I like my vegetables and salad. I’d love to lose 10 pounds, but that’s not happening, and I can’t see cutting back more on carbs.

  3. Thanks for another great post Dr. Attia,

    I have always been a “hard gainer” when it comes to adding lean muscle mass. Strength gains are usually consistent becuase of neuromuscular addaptation, but adding muscle is very difficult for me. My question is for an ectomorphic, carb-resistant person (and on a ketotic diet) what is the ideal way to add muscle mass? Do you know of any resources or have anectodal experiences that would help? Should I just learn be happy with my natural morphology? I think you partially addressed this on your reply to Nick M.

    Thanks, Eric

    • Eric, let’s throw this out to the group. I don’t know the answer beyond my hypothesis. Obviously, eating the *right* AA during and after the *right* kinds of workouts matters most.

    • Eric,
      Sounds like we share body types. I am skinny and always have been. When I work out consistently I gain a pound or two, my muscles develop better definition, but that’s about it. Do you need to be ketotic? Perhaps for we scrawny folk need to edge a little into glucose land in order to bulk up… but really my take is – “yes” to your question of being happy with your natural morphology, and assuming you are able to do what you want to do with your body. I mean if there is some goal (sport, athletic event, etc) that weighing an extra stone would help you achieve a higher level that is one thing, but there is so much to life, why sweat it if you’re ten pounds less than you would “like” to be? Probably easier to change your attitude.

    • Eric,

      Purely anecdotal, but here goes. Heavy, below parallel back squats. I’m more of a mesomorph but I ran cross coutnry in high school and 1 year of college. I added about 15 pounds of muscle in my early 30’s, when I ditched the leg extensions and leg curls, and starting doing heavy multi-joint exercises. Back squats was the cornerstone.

  4. I believe I have read every low carb, protein, insulin book and article in the world lately. In the end, aside from eating sugar and white bread all day, it’s still calories in and calories out that matters. Peter, are you telling us your eating 5000 calories a day and not doing enough activity to use those calories and your not gaining weight or fat? Is your entire blog suggesting we can over the course of a week eat more than we use and lose fat?

    Differing diets pushing one macro nutrient ratio over the other and even intermittent fasting all do one thing, the help a person consistently reduce calories.

    Calories in, calories out, with the exception of starvation type long term diets, is the only answer. Always has been, always will be.

    I tried low carb, higher protein, higher fat, aside from water loss, nothing happened. Nope, I was not over my maintenance level either.

    • Mike, I’m not saying that, actually. I happen to eat about 5,000 calories per day BECAUSE of how much I exercise. When I travel, for example, and can’t workout like I normally do, my caloric intake goes down. If you subscribe to Current Dogma, you believe weight gain is determined by the balance of calories consumed. In other words, fat cells will always accumulate fat based solely on the balance of caloric intake. The Alternative Hypothesis says something different — the more important factor from what you eat is how those foods actually impact the “choice” your fat cells make with respect to storing vs. burning fat.

    • Hi Mike,

      “In the end, aside from eating sugar and white bread all day, it’s still calories in and calories out that matters.”

      I think what Peter is saying is that, all though the “calories in/calories out” is true, it’s only a surface observation and that to understand why one person’s body will store fat while another’s won’t requires us to look below the surface.

      For example, you could say that all books are the same. On the surface this is true. They all have covers, pages within the book, etc. However, there are differences in the content contained within the book. There are fictional subjects and non-fictional subjects, romance novels and how-to manuals. Even when two people read the same book they will respond differently to what they read.

      So, back to “calories in/calories out” – this is only a surface fact. What Peter is encouraging us to understand is that under the surface, our bodies in general respond differently to what nutrients constitute the calories. And then even further below the surface, each person responds to those nutrients differently.

      Peter has given us a place to start, but it’s up to each individual person to take the information and experiment to find out what our own bodies need and how it responds.

  5. If you are looking for more topics to write about… 😉 I would like to know more about what kind of tests can tell me more about my body’s metabolism and condition, e.g. the insulin response test, and which you would suggest to get a good baseline on where the problems are or areas of improvement. Thanks for what you’ve written so far!

  6. Thank you for another excellent post!
    I am family physician and since I’ve started reading Gary Taubes and you I have changed the way I eat and also what I tell my patients to eat. Several of them have already thanked me and told me they feel much better, some of them also started losing weight. I must say that reading all this has completely changed my understanding of nutrition, obesity and my belief in “common wisdom” and “accepted medical practice”. It’s amazing what we have been taught for so long.
    I wanted to ask you about weight loss and a low carb diet. Let’s say someone removed all simple carbs from his diet – no sweets, no white sugar, no white flour, no rice, potatoes, pasta etc. He does eat a little whole grain bread, some fresh fruit and vegetables and the rest is cheese, fish, poultry, cream and milk. No Ketosis. Do you think that there is a need to limit the amounts eaten, or that it’s enough to eat according to appetite or hunger. We have learned for so many years that you cannot rely on hunger or appetite, that we all tend to eat much more than is good for us and that the only way to lose weight is to be extremely careful about how much we eat. If you say it’s usually not necessary to count the calories of the fatty foods going in, then where does the extra fat go? Excreted? Burned? It must be very easy to eat more cream or cheese than you really expend in daily living and excercise.

    Thanks again!

    • Mira, I wish more doctors could be as open-minded as you are and at least question what they have been taught. As a general rule, whether in ketosis or not, appetite is a good guide to returning our weight to our “programmed” state (which does not mean everyone is genetically programmed to have a BMI of 21), IF we consume foods that don’t aggressively promote fat storage. For about a third of folks this seems to result in more calories, the same calories, and less calories, respectively, but I don’t know exactly why?
      So, while it’s tempting to tell someone to eat as much as possible (as longs as they avoid carbs), this isn’t true, as it’s “forcing” the thermodynamic equation towards fat storage. Every case is different, given the complexity of the human body, so I try to avoid suggesting a one-size-fits-all “prescription.”
      I know this is frustrating, because you are looking at an ACTUAL person with all of their own genetic and metabolic nuances.
      It’s not actually clear to me that most people are overeating (beyond hunger) out of habit, for example. Certainly some do, but I think most people aren’t eating THAT many calories. They are eating too many of the calories that promote fat storage, which is a vicious cycle (the foods that promote fat storage tend to make you crave more of the same foods).

      • I do think it’s very easy to eat to many calories even while avoiding carbs. I love cheese, cream, nuts etc. I could easily eat much more of these if I wouldn’t stop because I know I shouldn’t. I do think it’s easy to overeat because you like the taste of something. It doesn’t have to be carbs. I wonder what happens to these calories.
        I just wanted to say that even if you cut out most carbs (and all simple carbs), you still have to watch what you eat.
        I do have a BMI of 21, and this is the most I have had all my life. I could always eat whatever I wanted to, but in the last years I had to start watching what I eat, and if I don’t – I gain weight. I’m 52. For the last few months I tried to cut out most of the carbs and eat mostly fat and protein, but I didn’t lose the 2-3 pounds I had hoped to lose. I guess there is no way around it – if you want to lose weight you have to eat less…

      • I would like to share some of my experiences with dealing with carbs like cereals, breads, pasta etc. I found out I simply could not “limit” my above carbs intake. One bowl of cereal deserved another, 1 slice of fresh hot sourdough – forget it, you have to have 3 or 4 while its fresh. Point being I could not be trusted with these types of carbs, so the only way to deal with them was to elimiate them. I also found that off the carbs I no longer experienced the sudden drops in energy and raging hunger. I also found that I just wouldn’t overdo foods like cheese or cream. I never felt the urge or need to eat them like I would carbs. Since ditching carbs about 3 months back, I have not overeaten in the manner I would have if there was bread, cereal, rice or pasta involved. The desire, the urge or whatever it is, just isn’t there. For the record, I was not obese, and would only consider myself 10-15kg over a very lean weight. I don’t count calories or weigh my food, and the weight (body fat) has steadily come off. While on carbs I would at times be driven to anxiety over trying NOT to go back for more of the same. I can’t imagine how overweight & obese people cope like this.

        • Anthony, I share your experience with respect to carbs. It’s MUCH easier for me to limit them absolutely (as I do now) versus when I was just reducing them heavily and still intermittently eating them. But everyone is different.

    • I agree with you, Mira. I’m 56 and could happily eat cheese and nuts all day – and if I eat “too much” weight comes on. I really would love to hear from more women, especially older women, on this issue. I love that Peter Attia is telling us he doesn’t KNOW, that we’re all different, that the science isn’t there yet. How refreshing to be told the truth! But, the more experiential information we all share, the more we can learn.

  7. Peter, thanks for the excellent article on CICO (calories in, calories out). However, you have one underlying assumption wrong, which is that the FIRST Law of Thermodynamics applies to humans. It doesn’t. The First Law applies to closed systems like car engines, which is definitely not us.

    It is the Second Law of Thermodynamics which fits your argument perfectly. For an explanation of this and a thorough debunking of CICO, see:

    There you will also read why your answer to Lal (#12) about what would happen if you ate enormous excess LOW CARB/HIGH FAT calories is incorrect. You wrote: “ASSUMING they can physically eat that amount of food… they almost certainly WILL gain weight.”

    Turns out, not so. You can read the actual data on the thread, but to summarize: “To prove how ridiculous CICO really is, two young, healthy male MagicBus members agree to eat excess thousands of high fat/low carb calories every day for a month, with no exercise. Their measured RMR was between 2300-2500 calories, so they agreed to try and eat double that amount, about 5000 calories a day. Eating that much is harder than it sounds; one of them (Jeff) resorted to drinking quarts of heavy cream daily to get there. Results after a month? One neither gained nor lost an ounce; the other lost weight.”

    Finally, in response to a comment you wrote: “In general …exercise per se does NOT seem to lend itself to sustained weight loss… However, people who exercise are often more careful about what they eat, and this confounding factor can create a bit of confusion around the process.”

    I believe the confusion actually stems from the LC community not understanding that how exercise affects individuals is no different than how sugar affects individuals with normal or insulin resistant metabolisms. It has nothing to do with being ‘more careful about what you eat” at all, but rather how your body processes what you eat, and how it processes *your* exercise.

    Healthy young men can exercise a lot and vigorously and as a result have their insulin sensitivity increase. Women with the insulin resistant variant of PCOS however, who are very sensitive to the insulin-suppressing effects of cortisol, only store more fat when they vigorously exercise. Once the PCOS is cured and insulin sensitivity is restored, they can exercise however they like to excellent effect. So I would say that exercise never *causes* weight loss (no matter how “carefully” you eat) but rather, in a healthy metabolism, it can help to maintain normal weight and fat levels.


    • Thanks for your great comments. While the First Law certainly DOES apply to car engines, it’s actually universally true for any closed system, including humans, assuming we define the closed system correctly. Same is true for the Second Law, as you point out.
      I’m not sure I agree, though, that EVERYONE who forces down, say, 3 times their energy requirement will NOT gain wait if they avoid carbs. It’s been true for me and about a third of people I’ve worked with (which, admittedly, is a modest number of people in absolute amounts), but I have seen more examples where this experiment results in weight gain. My point, I guess, is that this is complicated for reasons that extend past what I understand. I have observations, but I don’t yet have a unifying theory as to why some folks can do what I do and others cannot, with respect to eating seemingly unlimited fat calories.
      I think your point on exercise is interesting, but but I wonder if it’s even more nuanced than men v. women? I suspect type of exercise, genetic (beyond gender) differences, peri-exercise nutrition, and several other factors play a role. Great discussions, all around.

      • Hi, Peter. I’ve been busy with my own blog but really enjoy reading yours, and so I returned to read your reply to my comment. I fear I wasn’t entirely clear so let me try again:

        You wrote: “I’m not sure I agree that EVERYONE who forces down 3 times their energy requirement will NOT gain wait if they avoid carbs.”

        First, carbs aren’t the only issue. If you have the insulin resistant form of PCOS, then excess protein (even without ‘excess’ calories) will cause weight gain.

        Second, this is where most folks who claim that calories don’t matter (if composed of the correct nutrients for YOUR metabolism) fall into the double standard hole. Either a calorie is a calorie is a calorie — and the number of them you ingest matters. Or not. Because if not on the way up, it is not on the way down, either, no matter how many calories you eat if they are the right type. For you that is.

        And we have, in fact, proven this now many times over in the Protocol section of my blog. Once broken metabolisms are healed, calories do not matter if we eat the right kind of calories. I’ll talk about me in a moment, but want to say now that we have dozens of women who report daily (weight, meter readings, measurements) and who have done so for a year. The data is there for anyone to see. These women are ingesting, daily and over many, many months — an enormous amount of calories (a minimum of 1700 calories in FAT alone, not counting carbs and protein!) that is far above their BMR. Not only do they not regain any of the pounds or inches they lost, they continue to lose even more as they eat more over time.

        As for me, I am 5’4″. Five years ago I weighed 240 pounds, my measured body fat was 53% (that’s not a typo), my (then) undiagnosed blood pressure was 195/110, my leptin level was 35 and I wore a tight size 24 dress with a 51″ waist.
        At that time I was faithfully following my doctor’s advice by eating an extremely low calorie (1100 per day) low fat (10%) diet. And I got fatter and fatter. That’s right, on only 1100 low fat calories a day I was gaining weight. You would say “you were eating the wrong kind of calories” and of course you would be right.

        But the opposite must then also be true: if you do eat the right kind of calories for YOU, the number of them is immaterial because the body will simply burn off any excess it does not require. I don’t believe you can have it both ways: calories don’t count on the way up, but somehow do on the way down or when you’ve reached goal.

        Back to me. I created my Protocol and went on it. For the last three years I have weighed 145 pounds, body fat is 25%, my blood pressure without medication is 110/65, my leptin level is 8.5 and I wear a size 8/10. I am 64 years old, do not do strenuous ‘formal’ exercise of any kind, and I eat about 3500 calories a day, mostly fat, which is far in excess of my basal needs. I don’t gain any weight from year to year and I wear the same clothes which neither get tight nor loose. I’ve gone down 1.5″ around my neck, and lost 20″ from around my waist — all while eating enormous amounts of calories — the right calories for ME — every single day.

        My son, who is 6′ and who eats as I do, has a desk job and eats at least 4-5k calories a day, every day, certainly above his ‘needs’. He weighs 149 and his body fat is 6%. We sometimes laugh when we dine out and have a huge cheese plate for dessert after eating a huge meal, smearing butter on our brie and enjoying every bite. According to CICO, we say, we should be too fat to fit through the door of the restaurant! 🙂

        Needless to say our lipid profiles are great; his because he’s young, and mine, with TG’s of 42 and HDL of 97, because I;m eating the right type of calories for me and I know the number of them does not matter.

        You also wrote: “I think your point on exercise is interesting, but but I wonder if it’s even more nuanced than men v. women? ”

        I wasn’t actually talking about the difference in exercise between men v. women when it comes to PCOS, but that for men AND women who are insulin resistant, strenuous exercise that raises cortisol and depresses insulin raises blood sugars, and that means weight gain. I love to do heavy weight lifting but cannot, because within a few weeks of starting, I gain fat around the waist as my blood sugars increase. Hateful, but true. What I was saying about men v. women was simply that I believe the cause of, and treatment of obesity in them is very likely not the same. I believe research will show this to be true some day, and I hope that day is soon.

        Thank you for your excellent blog, and thank you for listening (even to ideas to which you might not agree). I do hope however, that you will come to sugarfreegoodies.wordpress.com and look at the data we’ve accumulated.


  8. I suspect you’ve addressed this somewhere, but I can’t find it.

    What do you think of the ability of certain foods – eggs, beef, etc. – to cause significant insulin secretion? Do you view this as less problematic than carb driven insulin secretion? Is there a good way to measure insulin levels distinct from blood sugar, and is there any point?

    • Protein certainly stimulates insulin secretion, though to a lesser degree than carbs. There is no reliable way to predict insulin levels (or ketones levels, for that matter) from glucose levels. I’ve tried several regression models from my own personal data and find them wholly unsatisfying.

  9. Yes, insulin plays a major role in fat accumulation. I believe this and like your discussion so far. However, I just keep wondering… It seems that after eating a particularly fatty meal I am much warmer and also my digestion seems to change as well, so it would seem that other factors are playing a role here, unless one thinks all this mediated thru insulin.

    • Just speculating here, but it’s quite possible that the lack of insulin is causing your body to partition more of the energy you’re consuming in the form of food into heat production, leading you to feel warmer. If insulin’s role is to increase the proportion of energy consumed that is stored as fat, that would make sense. Anyway, it’s an open question and I’m sure Peter will have more ideas, was just thinking out loud 🙂 Anecdotally, I too find that I am warmer on a ketogenic regime than otherwise (which is just lovely in the cold Northeast).

        • While thermogenesis might be part of it, I would guess the first order effect is in the energy content of what we leave behind in the toilet (as well as what we exhale when in ketosis — ketones have significant energy content, similar to alcohols). This is part of the first law of thermodynamics as Peter mentions, but seems to be routinely ignored. It’s astounding to me that studies (apparently) have not been done to quantify this important dependent variable.

          • Great points, Paul. This is why we need to do extremely rigorous studies in metabolic wards with metabolic chambers. There are folks out there, like Kevin Hall at NIH, that are leading the way in this field.

  10. Wow! Awesome blog and awesome, thoughtful responses! This is soooo much fun. 🙂
    I can’t wait for this info to hit critical mass. I know it will soon.
    I keep learning more about the influence of all hormones as time goes by but I have no doubt that insulin makes the biggest difference.

  11. Tapping a few of the concepts mentioned above (exercise, dogma, basal expenditure), one bit of dogma I’ve often heard and read is that exercise — of one form or another depending on who’s proselytizing — ramps up your basal metabolism for some period of time after working out. Hence another advantage to exercising. Do you know if that’s true or is that an old wives’ tale?

    • Kevin, the so-called “after burn” effect is not a wives tale (assuming you do the “right” kind of exercise). The question is (or should be), how CLINICALLY relevant is it? In other words, if I get an “after burn” of increased expenditure of 125 calories per week out, but my appetite — either that day or more often the next — increased by that amount plus the amount of calories I expended during the workout (if not more), does it help?
      There is obviously more to this, but clinical evidence has shown us that on average this effect seems to not make a difference in weight.

  12. I’ve often wondered about a possible exception to the alternative hypothesis in terms of exercise and fat loss. Let’s say I eat 100g of carbohydrates a day, for the sake of argument. Then I decide I want to start exercising everyday, but only satisfy my hunger with additional protein and fat to match my expenditure, while keeping the carbohydrate amount the same. It seems like in this scenario exercise would/might lead to modest fat loss, as the exercise would mitigate the effects of the 100g of carbohydrates.

    • Certainly possible. In fact, Neil, you’ll want to tune in for next week’s post where I talk (peripherally) about an example very close to the one you’ve described – not for weight loss per se, but for maintaining ketosis.

  13. Peter,
    Thanks for the great blog post. This was a big question for which I’ve been looking for a well-formed answer. As a chemical engineer with plenty of biology/biochemistry coursework, I think you do a great job explaining the science. Sometimes things get dumbed down for mass-consumption to the point where alarms start ringing for my inner skeptic. You don’t do this. This is just a very well-written and intuitive explanation for low-carb weight-loss/gain mechanisms as distinguised from the conventional wisdom. Keep up the great work.

    • Thanks very much, Mike. As you, it’s an important balance. My “desire” is usually to err on the side of overly complex, but I want to make the information is helpful, too.

  14. I really wonder if there is some formula that can be used to rebut or improve the laws of thermodynamics. As a case in point, myself, counting calories and measuring daily metabolic rate/burn and exercise output, I can tell you that the law can certainly be broken. As a more recent scientific test on myself, 90 days, calorie restriction, 1200 cals a day consumption of 90%+ proteins (1400 average with a measured weekly carb increase), and a BMR of 2500 (not including additional outputs) the math works out to a caloric deficit of OVER 100K over the 90 days not including any weekly exercise component. This should have been a long enough example of caloric restriction testing. And yet, while the math says the weight loss of any kind (it was literally ALL fat in this case from hydrostatic BF testing!!) should have been close to 30 LB, the actual total FAT loss (and overall weight loss) was 12LB. That would require a measurement error of over 100% which is simply not possible. can the body photosynthesize?

    How can the primary law be so wrong?

    • Cool experiment! Couple of things: 1) How did you calculate BMR and how often? It’s not static, so assuming it was calculated correctly in the first place, it was RAPIDLY declining with caloric restriction; 2) Hydrostatic testing is not particularly accurate, especially compared to DEXA, depending on body type. I once did a hydrostatic and DEXA on the same day and the difference was 4% (13% vs. 9%) — that’s a huge difference.

      • I did BMR using the o2/co2 measurement devices, once a month. estimated BMR (so resting) remained within about 10%, going from 2490 to 2300 at the end, so I wouldn’t say it is crashing. BF testing was all Hydrostatic, don’t have a DEXA lab nearby and it’s quite a bit more $$. Regardless, prior to DEXA, Hydrostatic was the gold standard with error rates of 1-3%, that isn’t 1-3% BF measurement error but 1-3% as normal. It SHOULD be relatively good for measurement especially with same process (same day of week, same diet, same hhmm, output, no eating for eight hours prior, etc.) I’d like the think that the measured move from 30% BF to 24.5% is pretty close to the MOVE, if not the most accurate nominal values?

        But what about the thermodynamics of it all? Why can’t it be better calculated and analyzed?

        • It can be much better calculated, but you’d need to lock yourself in a metabolic ward, under a hood, with precise calorimetry 24/7.

    • The body is not a machine that can be so finely calibrated and expected to operate so consistently. I think Peter’s diagram above is very instructive, showing “Energy In vs Energy Out” variables.

      The laws of Thermodynamics rest assured are not wrong or being violated. What’s happening is that your energy-out variables are simply different than you expect them to be, and probabably changing radically during the course of your experiment. Perhaps shouldn’t be a surprise that your body would react somehow to a semi-starvation nearly all-protein diet by becoming more efficient in conserving energy.

      The body’s not a calculator, it’s a steamy bag of wet chemicals. This is complex biochemistry, not simple arithmetic.

  15. Peter,
    What happens to unused ingested fats? Is it unhealthy to eat too much fat?

    • Not sure I understand question. What do you mean by unused? If fat is not expended (by the 4 ways we expend ingested food), it is stored.

        • For instance, you have turned me on to the heavy whipping cream latte and yesterday I had two of those. That is a lot of calories from fat. So, if ingested fat is not used as energy for the body it will be stored as fat and does not magically get eliminated from the body. The good thing about fat is that it does not trigger your body to create insulin, so it must become fat in your body by another mechanism?

  16. Thanks for another great post. I’ve been in ketosis for a month now, with ketones levels on my blood around 1 every time I check. Similarly to what some of the other commenters revealed, I too feel a bit disappointed about having lost only 7 lbs of weight so far, most of it during the first 10 days (my waist is also slimmer by 2 inches). I read about these spectacular weight loss rates that people seem to experience effortlessly, and maybe I just set my expectations too high. I keep wondering whether I’m doing everything right, though. My question to you is: what items should one check to “troubleshoot” a ketogenic diet and make sure everything is being done properly?

      • Thanks again. Following your tip I read an excerpt of the book and already ordered a copy. Looks promising.

    • Hi Alex – Sounds like we began ketosis about the same time.

      I have been restricting carbs since last summer – no sugar, no HFCS, no grains, just low glycemic veggies, but I was eating a lot of veggies and not in ketosis. 3 1/2 weeks ago I lowered my carbs to under 30 grams. I record my daily weights and daily body fat (by hand held Omron) on a spreadsheet, and calculate 7 day rolling averages, which smooths out the daily ups and downs. I keep a food log on fitbit, and have kept my protein in the 100-125 gram range. Based on the 7 day rolling averages, I am losing 1.6 lb per week total weight and 1.3 lb per week fat. I track my total calories eaten vs my calories burned (from fitbit) and watch my daily calorie surplus or deficit. I have found a strong correlation between the calorie deficit and my rate of weight loss. I compare my actual weight loss vs. calculated (from the calorie deficit) and find the actual weight loss exceeds the predicted, so maybe my basal metabolism is running a little higher than the estimate.

      We all respond differently. You might experiment with different amounts of calorie deficits, see how it affects you.

      • That’s the spirit, John. Well said. We all respond different. Best to do good (i.e., controlled and sufficiently long) self-experiments.

      • Thanks, John. I have been trying to keep things as simple as possible. Eat when I’m hungry. Measure my weight and waist line and check the ketones level on my blood once a week. Maybe I’m keeping things simpler than possible. I haven’t been keeping a food log. Perhaps it’s time to begin one.

    • Dr. Attia, thanks for pointing me to Phinney and Volek’s book. It’s a great read indeed. I’ve read it voraciously, troubleshooted my diet and I’m now shedding 2.4 lbs off my body per week. I followed John’s advice above, which is also stated in the book, and started to log everything I ate on fitday.com. As it happens, by just estimating what I’ve been ingesting (as I was doing before) I ended up eating too many carbs. Bringing the carbs back down to 20g per day did the trick. Interestingly enough, calories went down with the carbs (I know because fitday counts them automatically), as my appetite was more in control. I’m now as happy with my diet and energized as it gets!

  17. Peter, love the blog. I’ve been eating very low carb for about 8 weeks, and ketogenic for roughly 3 weeks. I have a general question about insulin: If a eat a meal high in fats with (for argument’s sake) 0 carbs of any kind, should my insulin remain completely unchanged? I remember the concept (Tim Ferriss – 4 hour body) that if you simply eat a normal meal slower, you’ll lower your insulin response (the sugar hits the system slower). Is this irrelevant in a ketogenic diet? Can I eat as fast as I choose? When I wolf down a meal, i used to feel that plummet in energy, now I feel an incredible rush of energy. Am I getting a blood sugar spike from the fats without any insulin (to protect me)? Could this be dangerous?

    • Not really an issue if you’re fully in ketosis as, by definition, insulin levels are so low (if they were not, you’d quickly fall out of ketosis). Fat does not stimulate insulin. When in ketosis, the greatest driver of insulin levels is actually protein intake.

  18. Peter: great series of articles and looking forward to further clarity of thought from you. 

    I feel after nearly two years with a generally low carb approach to diet my metabolic system has attained a high degree of flexibility. Such that I have achieved a good body comp which I can maintain comfortably by cycling between high carb days and near ketotic days. In some of my earlier efforts I struggled to maintain body comp though, believing the mantra just eat real food, and carbs don’t matter. I have shown to myself that carbs do matter, in the context that my metabolic systems were not running optimally to the extent that I could maintain a slight negative energy balance and control appetite so as to achieve body comp goals.

    I would be interested in your view on the debate about the role of carbs that has resurfaced and is nicely laid out at Richard Nikoley’s blog https://freetheanimal.com/2012/02/synthesis-low-carb-and-food-rewardpalatability-and-why-calories-count.html. The essence being that a number of LC and VLC are finding health benefits in introducing carbs back into their diet. 

    My interest in your approach, given the accounts of you and others, is toward the claimed mental acuity brought on with being in nutritional ketosis. 

    • Phil, thanks for passing along. My biggest hesitation when deciding to write a blog was that people would assume everything is binary — black or white. While there are SOME thing in biology that behave this way (e.g., action potentials), many things are actually shades of grey. The way our bodies maintain thermodynamic order is perhaps one of the greatest example of this phenomenon. So the “calories” discussion is particularly vexing, as there is a SPECTRUM. I do not doubt the veracity of Mr. Nikoley, but I equally do not doubt the veracity of countless others (myself included) who actually INCREASE overall caloric intake or maintain caloric intake when removing carbs for months to years, and still reduce fat burden. How is this possible? Great question. How is possible that 100 people can smoke a pack of cigarettes every single day for 30 years only 17 will die of small cell lung cancer (a cancer almost exclusively linked to tobacco use)? Another great question! We’ve got to recognize that an infinite number of genetic polymorphisms probably account for the different susceptibilities and predispositions we have.
      I would like to take the “debate” to a state of hypothesis testing. Not mickey mouse self-experiments like I’ve been doing my whole life, but REAL metabolic controlled experiments where we test one variable at a time and start to parse out the nuances.

      • Peter,
        You may label your experiments as “mickey mouse” in comparison with the real science you would like to achieve with NuSi, but please keep in mind that those experiments, no matter how “mickey mouse” they may seem, are helping all of the people commenting here – which is a lot!

      • Thanks Peter, yes agreed re the shades of grey. And on reflection my points should be refocused toward what health/performance/life goals are wanting to be achieved. With LC or VLC, being but a pathway or mechanism toward an outcome, in this case combined with managed protein consumption, nutritional ketosis.

        I agree with you regarding the mickey mouse self-experiments in the context that a lot of this “science” is relatively immature, given just how much we dont know. I think the upside is that people do have to self experiment, and it will be interesting as to what rational information you will be able to produce to guide future generations in how to improve their health. Or will nature and individual variability continue to confound us. Interesting times!

      • The real issue with Richard’s post and others is that they no longer think insulin is a major contributor to weight gain and ill health. I don’t always eat VLC, but I also don’t agree with the Food Reward theory.

        Peter: have you looked into this theory as valid? I know taubes has a great post countering this, just wondering what your opinion is?

        Another question Peter, since you are so great at responding. If someone stalls on a low carb diet, would you recommend lowering protein before increasing carbs?

        I have always recommended this, but it seems that people coming from the Atkins approach don’t think too much protein can cause any issues. Just a small example: both my wife and my brother had issues on a low carb diet until they controlled their protein intake. My brother, for example, was eating a ton of beef jerky, which is almost all protein and no fat. He was getting migraines and started blaming it on the LC diet. I recommended not eating so much protein and switch to higher fat snacks like Mac Nuts and Almonds. And my wife started cutting out the whites on just one of her two eggs and that made a big difference.

        I know that everyone is different, but it seems that the “paleo” community now recommends adding carbs instead of lowering your protein.

        Interested in your thoughts.

        • Elton, I have yet to be convinced that the food reward system is the FIRST ORDER term driving obesity. I don’t doubt, however, that it could play some role for some people. I just do not believe it is the primary driver to what is going on. Part of the problem (and we are ALL guilty of this – me included), is we tend to focus on the hypotheses we find most convincing, sometimes at the exclusion of giving equal consideration to others. It’s an inherent bias problem is science. The key is being open minded enough to at least ask questions.

          My response to the plateau problem is very individual. It varies by so many factors, I can’t really say definitively what the answer is. I do tend to experiment with protein reduction first, if intake is north of about 120-150 gm/day.

  19. Great article, and thanks for responding to comments so diligently.

    On observation I have had, is that when we argue against the simplistic conventional wisdom “calories in/calories out” model, body temperature should be taken into account. We are not all at exactly 98.6 degrees all the time. Our bodies are not perfect Newtonian machines that obey a strict energy in / energy out balance. To say so is to ignore that our metabolism can and does adjust to different circumstances. We burn different fuels, at different rates, depending on a multitude of causes.

    Just an observation.

    • Certainly. Thermogenesis is part of the equation, as it drives a large part of our metabolic expenditure to maintain body temperature in such a narrow band.

  20. Dear Peter,

    Thank you for all you do and for being so inspirational! There is so much great instruction in these posts; I wish I could find things easier; for instance, I read somewhere that I should increase salt and fat. I wanted to know how much to be consuming, but I have been pouring over all of the comments and articles, and I can’t find where I read it.

    I have just begun this way of eating, and I have a dilemna. As a practicing Catholic, I am stuck with no ideas for the many meatless days during Lent. Ordinarily, my husband and I would have a peanut butter and jelly or cheese sandwich for lunch and ravioli or pasta for dinner. I can’t cook/wouldn’t know what to buy/don’t like fish. I can’t think of anything but scrambled eggs or omelettes for protein. (I don’t think we are supposed to be eating a salad without a protein, is that correct?)(Doctor nixed canned tuna I used to give my husband because his mercury is high). I can’t find a low-carb protein bar that doesn’t knock me out of ketosis (according to ketosticks). Would you have any ideas to suggest for meatless days and do you know of a bar that is truly low-carb? Thank you so much 🙂 maryann

      • Thank you Doctor, I will get this book. I have read WWGF and recently ordered GCBC. I appreciate all of your help, maryann

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