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 Dogma? Current 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.
You’re extremely inspirational. Is there a way I can personally contact you?
Contact page
Hi Peter,
I came across this study https://carlcam.co.kr/2006/ECS/sub05/pdf/9_10-10.pdf . I’m puzzled by figure 2 as I would have expected a line with a positive slope so that a greater reduction in serum insulin levels over the 6 weeks would have resulted in the greatest fat mass loss and change in body fat %. The authors also state “Inhibition of lipolysis occurs at relatively low concentrations of insulin with a half-maximal effect occurring at a concentration of 12 pmol L-1 and a maximal effect at a concentration of about 200 to 300 pmol L-1.10 The significant reduction in insulin from 23.7 to 15.6 pmol L-1 may have been permissive to mobilization of body fat on the carbohydrate-restricted diet.” Which seems contradictory to the figure.
Am I misinterpreting the figure or what is going?
Keep up all the good work you’re doing! Yuo have no idea how much it means to us, even those of us who struggle with the problem of underweight (especially after going low-carb and now ketosis).
Sorry, Hemming, I can’t see the figure you’re referencing.
https://www.colorado.edu/intphys/Class/IPHY3700_Greene/pdfs/discussionEssay/weightLossStudies/Volek_diet.pdf
Hopefully that link works (even though the quality is poor).
Repeat question?
I would have expected that those who had the biggest drop in serum insulin also lost the most fat. But that doesn’t seem to be the case. For instance there is one who had a 50% drop in serum insulin but still gained ~0.5kg of fat.
These are pretty good correlations, actually, for a “biological system.” Doesn’t prove cause, of course (i.e., the reduction in serum insulin caused the loss in fat). To get at that you’d need to look at other experiments. But it does certainly support the role of insulin in regulating fat accumulation vs. lipolysis. There will always be outliers to every multifactorial biological hypothesis. Most overweight people also have elevated leptin…but not all of them. You get the idea. This is a good paper.
I still dont understand the slope of the line. As it is shown in fig. 2 it would indicate that a higher insulin level would induce the biggest loss of fat mass.
Isn’t it showing the greater the reduction in insulin, the greater the reduction in fat mass? That’s my read.
The text clearly suggests that hypothesis (which I would also have expected). But when I look at fig. 2, I still can’t can’t get my head around the axes. Those with the lowest decrease in insulin are showing the biggest fat loss. There is one who lost ~5kg of fat with an ~8% reduction in insulin level. Comparing that to the other one I mentioned it seems like insulin is a good thing for fat loss.
I’m pretty sure this is a sign issue which is confusing me. Anyway, I just wanted to hear how you read the figure.
Thank you.
Hemming, I went back and looked a second time. You were right (and, by extension, I was wrong!). I was puzzled by this, so I shot Jeff Volek an email. His response:
“In this context the guys were young and normal weight and had relatively low insulin at the start and so even small changes translated into relatively large percent decreases. Going back to those original data it is clear that there is no correlation when the absolute change in insulin is plotted against fat loss.
In contrast, in our studies with obese subjects, there is a significant correlation between decrease in insulin (pmol/L) and fat loss.”
Ok, thank you contacting Volek. Then it makes sense 🙂
Given the curvature of the (in)famous insulin/lipolysis curve even small absolute changes can make a difference – at least just from looking at it in one of your other posts. I have no background in medicine though so I dont know how closely it generally fits the individual.
In any case, mystery solved.
Hi Peter, great work! my question for you is – In your opinion is it more important to be in a high level of nutritional ketosis (over 1.5mmol) Or, if one should be more concerned about keeping overall calorie intake low when trying to lose the last few kilos.
I ask because I’ve been stuck at 18% body fat 6 months now so have decided to count calories (I noticed I’d been overconsuming calories) to achieve my goal of 10% body fat. While restricting calories, I do find it very hard to get my ketone levels over 1 mmol even while eating 70 – 80% fat, 15% protein and 5% carbs.
Would you recommend increasing fat to get into higher levels of ketosis or to disregard ketone levels and concentrate more on restricting calories?
I’ll address this in the remainder of the ketosis series.
Hi again Peter,
Sorry for bringing up all these studies but I think this one https://ajcn.nutrition.org/content/26/2/197.full.pdf is more interesting than the first one (perhaps you’re already familiar with it).
It shows that even an intake of 600g fat/day did not induce weight gain. That is interesting in itself. What I was more surprised to see was that the correlation between fat intake and weight gain was less pronounced for corn oil than olive oil. The researchers contribute this to the higher LA content in corn oil. Do you have an explanation for this as I would have thought that reducing omega-6 would be more beneficial? Could it be because corn oil (per g) is higher in essential fatty acids?
This was one of the 84 studies or so we reviewed at NuSI (https://nusi.org/the-science/review-of-the-literature/#.UOBlKm9Pyg4). Main takeaway is that the study was too poorly done and reported to draw much conclusion.
Interesting. I had not seen that list before, its very useful to have as a reference when going through papers. Will it continuously be expanded?
I do think that the idea of the study is interesting as I’ve seen other n=1 experiments which also consisted of a very high fat intakes that did not result in weight gains.
Hi, Dr. Attia
Most people who promote calorie counting don’t realize that :
Calorie labels are wildly and enormously inaccurate. This is to the tune of 10 % to as much as 80 % off as Dr. Jeffrey Friedman points out.
And even if there were accurate nobody could consciously match expenditure to intake with the many millions we consume over a decade. Calore counting is a completely false illusion.
Take care,
Raz
Dear Raz –
1. Wrong – “Calorie labels are wildly and enormously inaccurate. This is to the tune of 10 % to as much as 80 % off as Dr. Jeffrey Friedman points out”
You expect me to believe this crap ? To indulge yourself in some insane form of anti-calorie counting is interesting only in the aspect of how one idiot sheep is more than willing to follow a leader idiot sheep –
Frankly – I’m tired of this nonsense being parroted as it causes a gret deal of harm – it hurts people – it solves nothing –
2. Anyone – can test this for themselves – eat as much fat as you like – stay in ketosis – and watch the pounds melt away –
What F————- nonsense – it’s a game you can’t win – if those fat calories equal or exceed your bodies needs
Jeff, maybe I’m wrong, but I though Raz was making the point that calorie labels may be far enough from accurate measurements, that even if you wanted to could them this way, it might be tough to balance.
Hi Dr. Attia,
Your blog and research is brilliant combination of scientific evidence and anecdotal support, and your journey toward health, heretical as it is, is inspiring. Thank you.
I believe you noted in one of your lectures that after taking on the first few step of a low-carb diet, you tested insulin response to glucose and found that it was a much more modest insulin response than on your previous high-carb diet. Very interesting. A question regarding insulin sensitivity: I’ve heard that that long-term exposure of cells to ketones retard insulin-induced activation of the insulin surface receptor, thereby making a ketogenic dieter more sensitive to carbs once added back into the diet. What’s your take on this, Dr. Attia? Thank you
Very good question, and one we don’t know the answer to. “IR” is a broad term. Do we mean liver, brain, muscle, fat cell? All have different responses, but crude measures like HOMA-IR just average them all together.
Hi Dr. Attia,
I have struggled with my weight my entire life. I lost about 50 pounds in 2012 and have kept it off now for about 9 months (with about a 5 pound swing). I also started weight training in 2012 and have significantly increased my lean mass (in addition to the significant fat loss). The weight loss is attributable principally to significant carb reduction (although I still eat about 100 grams of carbs a day- mostly vegetables, occaisional berries, and carbs from dairy and nuts- I have cut all grains and legumes from my diet) and to “Leangains” style intermittent fasting. I weight train 3 times a week and do indoor cycling (spinning or computraining) once a week. I have not done a DEXA scan, but based on caliper testing my body fat is now at about 21%. I would like to get a little leaner and have tried reducing carbs further but I find that I am ravenously hungry when I limit carbs to below 50 grams and proteing to 150 grams- somehow I can’t seem to fill up enough on fat without hitting insane calorie intake (upwards of 4000 calories). When I eat to satisfy my appettite I end up gaining weight (because I end up eating loads of cheese and high fat meats). I have put tremendous effort into being mindful about when I am truly hungry (eating slowly, paying close attention to hunger cues, etc) and honestly believe that I am only eating when I am hungry (and not eating emotionally, solely for pleasure, or for sport). Are there some people who simply cannot rely on appetite as their cue for how many calories to consume? If so, what could account for this and are there any solutions that you can offer? Many thanks.
I’ve been trying to navigate through your blogs to find this answer, so I apologize for these possibly dumb questions:
1. Is there a continuum of benefits (of any kind: insulin sensitivity, weight loss, trig reduction, etc) seen from a continuum of CHO reduction?
2. Does the source of CHO matter? I saw your graphs from your ‘personal journey’ blog (how you gradually reduced CHO and your bloodwork associated with each stage). But while I’m getting that you say a calorie is NOT a calorie, is a carb NOT a carb? Or is a carb is a carb is a carb?
3. I also saw a response in one of your question and answer sections: Q:”Is ketosis for everyone?”. And you said something like “definitely not”. How does one know if they should try it? It seems like quite a challenge for most people.
Thanks for your work on these topics.
Jessica,
Hopefully Peter will jump in with his thoughts. Here are some of mine: First, remember that individuals vary a great deal.
1.I don’t see a ‘continuum’ of benefit from reduced carbs, but more like ‘steps/stages’ which can provide benefit. For example, cutting out sugar; cutting out grains and other starchy foods ( low carb); ketogenic (very low carb).
2.If the person has any signs of insulin resistance/ carb intolerance/ blood sugar fluctuations, then I think the source of carbs matters (as well as the quantity). Rapidly absorbed carbs (sugar/ corn syrup, etc) have a negative impact compared to the carbs in something like broccoli/cauliflower/cabbage.
3. For many people getting into and staying in ketosis is harder than low carb; so whether you should try it really depends on your personal situation…what do you want to improve? Do the benefits that people report match your goals?
I’ve been doing low carb for almost two years. I started out gradually, using “Life Without Bread” as my initial guide. I did a lot of reading. I gradually moved my carb count down; using “The New Atkins for a new You” , “The Art and Science of Low Carbohydrate Living”, and “Primal Body Primal Mind” as guides.
I’ve lost 60#, going from 230# to 170#, and have observed a number of health benefits.
I’ve tried and gotten into ketosis (barely) twice before now; blood ketones generally in the 0.5 to 1.0 range, but occasionally dropping below 0.5. The first time I stopped because I like to do multi-day hiking/pack trips. I had not figured out how to stay ketogenic using dehydrated foods. The second time was traveling and again having trouble with not having the right foods on hand.
I don’t have it all figured out yet, but I’m finding that I need to not only eat very low carb, < 20 grams of net carbs, but also moderate protein, < about 80 grams, with only a small part of that coming from dairy protein, and not too much of the daily protein allotment at any one meal.
I’ve been on a ketogenic diet again the last two weeks. I’m having more success this time…primarily by getting my fat intake up. This has moderated my appetite, so it’s fairly easy to keep the protein down. What I’ve changed about my fat intake is adding a cup, or two, of ‘fat’ coffee/decaf a day (with a generous amount of coconut oil & heavy cream). I’m also putting more butter on vegetables, pouring the ‘drippings’ from cooking meat, over the meat when I serve it, and things like that.
In comments under Dr Attia’s blog “Ketosis – advantaged or misunderstood state? (Part I)”, there was a comment about using a ketogenic adjunct such as coconut oil, MCT oil, or AAKG (Arginine alphaketoglutarate). I had not heard of AAGK before…so googled it. There’s not a lot of info available…much of it is related to AAKG being sold as a supplement for strength training and fitness. I found enough bits & pieces to decide to buy some AAKG and give it a try. I’ve been using it in a ‘keto broth’…broth with coconut oil, heavy cream, and 1 scoop (2 grams) of AAKG. I’ve been drinking it 3 times a day. To me, it has a somewhat tangy/ lemony flavor…I like it. It seems to boost my ketones 0.5 to 1.0 above what they would otherwise be. I think this has also helped me get into ketosis…with ketone readings in the 2.0 to 2.5 range, where 1.0 was as high as I’d gotten before.
It has been a challenge, but for me it’s been worth it. I’m sleeping better, and have noticeably more energy. And, the minimal hunger has made it relatively easy to stay with the diet, once I figured out what to eat/drink.
Is carb resistance the same as inulin resistance?
No, but they are related. IR is a very complex state and involves many organs. One can have IR at the levels of different cells (liver, fat, muscle, neuron).
Do you use carb resistance and insulin resistance interchangeably? People who insulin sensitive aren’t prone to weight gain, but I saw in a comment that you said that someone who couldn’t gain weight was carb resistant. Is it that people who are deemed insulin sensitive are actually insulin sensitive on their muscles cells but not their fat cells?
Hi Dr. Attia
I fully support you and your efforts. I wanted to tell you that most poeple are applying a closed system equilibrium thermodynamic approach to humans . I have spoken to some of the very best biophysics professors from Oxford, Caltech and Cambridge and what they told me is this:
*The human body is an open system
*The human body is a non- equilibrium system
And because of these two facts, this makes the situation hellishly complex to the maximum. If we could evben come up with some equation- it would not be singular. It would be many equations. None of the scientists I talked to could even give me a rough idea of what this might look like and admitted as much. These are top minds too.
We have to consider free energy ( which includes entropy) rather than energy. This area of thermodynamics is extremely subtle.
Nobody mentions the sun either. or skin temperature, or the fact we excrete energy.
I have it on top authority that fat and muscle gain and loss have to do with extremely complex physiological and biochemical processes- it’s not a basic thermodynamics problem. These were the words of the scientists.
Best Wishes,
Raz
Thanks, Raz. All of these can be measured in sum (though not necessarily in isolation), via indirect calorimetery or even doubly labeled water. So I don’t disagree with your point, but it doesn’t change my argument. My point is that something other than *only* caloric balance can drive fat accumulation, *and* this does not violate the First Law. I could not agree more that the First Law is a meaningless way to think about physiology. It’s obvious, and it adds no value.
Peter –
You said: “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.”
Are you speculating here or are there controlled studies that support this?
I don’t think this exact experiment has been done, though slightly less interesting variants have. It would be a very elegant experiment, and we have discussed it in great detail.