It's a fact that the energy coming into the body minus the energy coming out (including that burned through activity), equals the energy being stored. I think the way Gary Taubes shows it is like this:

Ei - Eo = Es

Where Ei is energy in (measured by calories, but it could be BTUs or whatever), Eo is energy out, and Es is the change in energy stored. That's the First Law of Thermodynamics that calorie counters like to cite, and they're right -- as far as it goes.

What's not a fact is that you can equate Ei to "food eaten" and Eo to "exercise plus a constant amount used for basic functions of life". That's where most people oversimplify it, and get the idea that if you just eat 100 calories less or exercise 100 calories more, you'll lose 100 calories worth of energy storage (hopefully fat) like clockwork. That's hopelessly simplistic, and ignores other inputs and outputs that can affect the equation.

Part of the problem is that people assume the left side of the equation drives the right side, as if the body is like a shopping bag, and if you put two items in and take one out, it has one remaining. Do that every day for a month, and the bag is bulging and in danger of bursting. They assume that your body has no say about any of this; it just stores any extra and gives up some when there's a deficit.

It's more accurate to turn the equation around and make Es (change in energy storage) the driving force. One day your body decides it needs to store some energy. Maybe you're 12 years old and starting a growth spurt, and it needs to build a lot of bone in a hurry. Maybe your fat cells are requesting more energy to store because they aren't getting the leptin signal properly. Whatever the reason, your body says "give me more energy to store," and it's pretty easy to eat a couple hundred extra calories a day without knowing it, if your body is doing something with it so you don't seem any more full. If you're weighing your foods with great accuracy and have the willpower to keep Ei from increasing, your body will have no choice but to do whatever it can to bring Eo down instead. You may start to feel lethargic, less ambitious about exercise, moving more slowly, sleeping longer.

The point is that if your body decides to store energy, there's not much you can do to stop it by trying to manipulate Ei or Eo directly. If you refuse by reducing your Ei at least as much as your body can reduce Eo -- and you've got tremendous willpower or are in a controlled environment like a prison where someone else controls your intake -- then you're starving yourself, which isn't good. On the other hand, you can address the root cause of why your body is trying to increase energy storage, which people are really just now starting to explore seriously, with topics like leptin resistance, fructose damage to the liver, various inflammatory problems, etc. If we can figure out how to control Es (and paleo is a step in that direction, but there's a lot to learn yet about the specifics), Ei and Eo will fall into line.

Here we go again. First, the link to a good thread on this. Also various answers by pfw are helpful, e.g., here, here, and here. So we could close this as a duplicate thread, but we have a good discussion going already -- so why not continue.

I think everyone is right so far. But because in different cases people are using different terms there ends up being an appearance of disagreement.

• Do calories matter? In the broadest sense, yes, obviously, and in fact it's a tautology. Weight gain does equal calories in minus calories out, because we live in the universe we live in. But you have to see that many different things can go into that "calories out" term of the equation in order to see how the equation can be preserved. Your body has ways of burning off excess calories rather than storing them. As Taubes points out, the body can set up various "futile cycles." It can generate heat. You can fidget. This is how your body can make the "calories out" term higher in a sneaky way. On the other side of things, your body has ways of conserving energy: it can make you sluggish, performing fewer tasks, and it can make you perform the same muscular task more efficiently. This is how your body can make the "calories out" term lower in a sneaky way.

• Do calories matter? If by this you mean "can you lose weight through increasing calories out and decreasing calories in" then the answer is: 1. usually no and 2. sometimes yes. Usually no because a. calories out and calories in are not independent variables and b. there are "sneaky" ways by which your body can change calories out that escape your conscious control (see my last bullet point). Put these two together and you see the trick: If you consciously increase calories out (exercise) every day while decreasing calories in, then your body will unconsciously decrease calories out (make you sluggish, perform tasks more efficiently) to compensate. The result: you don't lose weight. So if by "do calories matter" you mean "are the laws of the universe preserved" then the answer is yes. If by "do calories matter" you mean "can you lose weight through increasing calories out and decreasing calories in" then the answer is no. (The same logic applies to weight gain.) Now I said 1. usually no and 2. sometimes yes. That was 1, usually no. Here is 2: Your body can only do so much compensation through the "sneaky" mechanisms. If you eat 0 calories a day for a very long time then you are going to lose weight. If you eat 7,000 calories a day for a very long time and you are otherwise sedentary then chances are you are going to gain weight. (There is a slight asymmetry here for obvious reasons.) Now the limits of what your body can do are somewhat uncertain, as Aaron B. pointed out in his comment to Ben. Maybe some people will gain more than others, maybe some people will gain for a while and then stop. It all depends on how powerful the "sneaky" mechanisms are. So to go through it again for part 2: If by "do calories matter" you mean "are the laws of the universe preserved" then the answer is yes. If by "do calories matter" you mean "can you lose weight by increasing calories out and decreasing calories in" or "can you gain weight by decreasing calories out and increasing calories in" then the answer in this case is also yes. You are overriding the "sneaky," unconscious mechanisms with massive overfeeding or massive underfeeding -- huge variations in the conscious mechanisms.

• Do calories matter? If by this you mean "is the only way to lose weight to make yourself hungry all the time" then the answer is: No -- go paleo, dammit. This follows from the above: a conventional "diet" is just a diet that falls into the "sometimes yes" category in my previous bullet point. In order to lose weight with the conventional method you have to override your body's "sneaky" mechanisms. What this means is that you have to go to extremes. In other words, you will be hungry and irritable all the time. If you go paleo then you are taking those sneaky mechanisms and making them yours. Because hormonal readjustment is a sneaky mechanism too -- in the sense that it is something your body does for you; it is something that happens unconsciously rather than consciously. When you go paleo your body decides to be the kind of body that doesn't need a big gas tank rather than the kind of body that does need a big gas tank. How you get to that point -- the increasing of calories out and the decreasing of calories in -- is not all that relevant. It will be, for all intents and purposes, taken care of by your body for you.

As a small postscript, I should say that there are a couple more complications. I think that there might be some new role for calorie counting when you get down to lower levels of body fat. And there is also the issue of those who have caused some previous damage to their body such that satiety can't be relied upon as a signal. But the first of these is complicated and left for a better time, and the second of these has been discussed in a very interesting way in this thread started by SherpaMelissa, as well as in the thread of hers I linked to at the very beginning of my post.

the real issue with calories in and calories out is that your body is a mutable entity that has different energy needs based on an almost infinite number of variables with additional variables concerning how efficient that body's metabolism is on average. On top of that the kind of calories you're ingesting further affects that metabolism's efficiency.

I tend to think those who argue against calories in/calories out do not exactly argue the science of energy input and energy output as much as they are arguing against the notion that a certain "caloric ideal" will optimize your body.

The problem with "calories in/calories out" is that it tends to lean towards a "caloric ideal", usually expressed as a set number that should be approximated every day, which ignores the body's varying needs and desires. personally i tend to think this is very destructive to ignore or override your body's instinctive needs repeatedly because it disrupts your sensitivity to informative natural processes in the long run and then you develop metabolic disorder. This idea has been complicated by food production which substitutes unacceptable "cheaper" calories that "mimic" the desired natural calorie source.

You can pee calories out and your body can change its temperature. Your body can convert fat to muscle and vice versa. All these things affect the calories out part of the equation in different ways.

Calories in vs calories out is accurate enough, the problem is most people simplistically equate it to mean food in minus exercise done.

The point is that yes, hormones affect the way your body deals with whatever calories it gets.

My own example at 31 years of age: I eat 3500 to 4k calories per day and i'm maintaining a lean physique. This is because im lifting heavy and my muscles use the extra cals to heal and my hormones are firing well. My body is being essentially abused in a controlled manner by my lifting schedule and thus needing repair on my off days to come back bigger and stronger.

If I were not giving my body a growth stimulus by lifting progressively heavier things regularly and eating big then I would simply get fat.

All the back on and forth on this thread can be summed up with:

the two ideas of 1) calories counting or not, and 2) hormones affecting HOW those calories count are NOT MUTUALLY EXCLUSIVE. something Dr. K seems to misunderstand.

I have quickly scanned through this thread and comments, and one point that (I think) has yet to be made is that given the formula:

Ei - Eo = Es

We take it to mean that the LHS side of the equation (E in - E out), is driving the RHS of the equation (E stored).

But this is not the case. Through hormonal control Es can and does drive 'Ei - Eo'. This is perhaps THE BIG POINT made in GCBC as it goes against conventional wisdom and our approach to weight control for the last 50 years. Your obesity is making you eat more. Your obesity is making you do less.

The other point is that Ei and Eo ARE NOT INDEPENDENT VARIABLES. One can be adjusted based upon the other, dynamically and way below your physical control.

It is also worth pointing out we are not closed systems or bomb calorimeters. There is uncertainty about which metabolic path a calorie will take at any given time. Also, biological systems can undergo autophagy. Try controlling 'calories in' in a system that can eat itself. Try controlling 'calories out' in a system that can adapt its thermogenic activity and futile cycling with impunity.

So when the OP asks "...is it really true that eating this way allows you to eat until you are full and satisfied, and not gain weight as a result of too many calories?"

The answer is yes, if you have a healthy, functioning metabolism.

Truth. Calories count period. Eat 7000 calories of ANYTHING and you'll gain weight. Very simple. Try it out. You can always cut weight later.

There is alot more to the reasons why people on paleo don't eat grains and legumes than "because cave men didnt farm then, so therefore its not paleo" Grains and legumes are UNHEALTHY and there are many reasons to avoid them. In fact, besides eating whole foods, the basis of paleo is about avoiding these foods.

I say it's a half truth, or as Dr. Eades says (paraphrased from Protein Power) 'ultimately calories count.' Most people can't eat 8,000 calories a day and not gain weight, and if someone starves themselves by eating 1,200 calories a day, they'll most likely lose weight.

I say it's a half truth because when people start focusing on calories they just eat less of the crappy foods that got them unhealthy/overweight/diseased etc and partially starving oneself is shown not to work long term.

So yes, if you stuff your face you'll probably gain weight, and if you starve yourself you'll probably lose weight, BUT, if you eat the right types of foods you simply don't have to worry about it.

The formula:

(Calories in) - (Calories out) = (Calories gained)

is a fundamental law of physics. Short of surgery there is nothing in the world that can alter it.

However, what is often left out is the fact that what kind of Calories you take in, in what form and when, can have a dramatic effect on both how much you burn and how much you want.

Hormones control your appetite, your metabolism and your body's preferred fuel source. The kinds of food you eat affect your hormones.

It's also true that there are other things that can affect your hormones, so no two people are going to see exactly the same results from a paleo diet, but most people coming from a high-carb diet will lean out and be less hungry with no additional effort.

So yes, Calories in-Calories out is true, as far as it goes.

And yes, eating paleoesque foods sensibly will smooth out your appetite and help you tend toward a healthy weight.

Welcome to PaleoHacks. :)

All I know is that I am 5/'8, 158lb male, 26 years old, and I am eating well over 3500 calories a day ( have a bit of an obessive eating disorder I think b/c I eat just for fun all day) while staying lean 6-8% body fat. I rock climb 3 days a week, and my job involves standing all day ( I work at Whole Foods). So maybe, I am underestimating how many calories I need per day, but something tells me that excess calories don't automatically = fat gain.

Calories dont matter....they matter if your hormones and metabolism are off. And most peoples are. Read the laws of adiposity in Why we get fat. It will help you understand why. Anyone who tells you calories matter in every context should be ignored because they dont understand biochemistry. Its that simple. Sadly most of america does not get it.

Calories in and out count for your weight gain or loss, quality of that gain or loss (fat and muscle increase and decrease) depend on the quality of the calories in and the exercise done plus some hormonal stuff thrown in there.