Calories in vs Calories Out: Fact or Fiction?

Calories in vs calories out: photo of sandwich with a tape measure

You may have heard, but calories in vs calories out is a myth and fatness is actually all about hormones and carbohydrates. You may have also heard the exact opposite, that calories are all that matter. So what’s the truth, and which angle should we tackle body composition from?

If there’s one subject sure to bring out the logical fallacies and nonsense it’s the calorie debate. What normally happens is that people shoot down an exaggerated and ridiculous version of the opposite side’s argument (otherwise known as a straw man).

No one is served by the misrepresentation and speaking past of opponents that occurs during these discussions. So for a change I’m going to do my best to present the most charitable interpretation of each view as I understand it.

The Insulin Hypothesis Side

This argument lays the blame of fatness mainly on dysregulation of the hormone insulin. It hinges on different foods having very different effects on body composition (“a calorie is not a calorie”), meaning that calories in vs calories out equations are basically useless.

The caricatured version of this perspective is that body composition is completely unrelated to energy intake and that people get fat solely because their diet is made up of a high percentage of carbohydrate, regardless of the amount. “Myth busters” of this ridiculous straw man point out that you can’t break the laws of thermodynamics, and the debate goes around in circles with nothing productive coming of it.

I think the real argument here is that overweight is sparked by hormonal disruption from intake of refined carbohydrate, especially that found in the most highly palatable and rewarding foods. This in turn causes an urge to eat even more refined carbohydrate and food in general, and the eventual result is overweight and obesity. It’s more about the initial cause of the problem, with the emphasis being on the types of foods we eat as opposed to the amount.

What’s meant by “a calorie is not a calorie” is that a calorie’s worth of food will have a different effect on body composition depending on exactly what food it is.

I don’t think any educated proponent of this view is saying that the amount of food eaten is completely unrelated to fat gain—again, rather that the urge to eat excessively is caused by hormonal dysregulation from consumption of highly refined, highly palatable foods in the first place.

The Calories In vs Calories Out (AKA Energy Balance) Side

The straw man version of calories in vs calories out: the calorie value of a food is all that matters, and a calorie’s worth of any food or macronutrient will have the exact same effect on body composition. Like any straw man argument, the absurdity of this idea makes it very easy to disprove—even at face value it’s obviously false to anyone with a passing interest in nutrition and physiology.

Part of the problem is that attempting to summarize with the phrase “calories in vs calories out” invites misinterpretation.

But again let’s uncover the true essence.

What’s really meant is that the most significant cause of fat gain is the net energy the body receives (after digestion of food, bodily maintenance, and activity), and that hormonal dysregulation is a result of excessive fatness as opposed to the cause. (At least in a person who was healthy to begin with—it could be a different picture for people who have preexisting pathology such as diabetes or low thyroid production.)

It’s a Matter of Emphasis

The views aren’t completely opposed. The nuance is where each side puts the root cause of our body fat woes. One side says our fatness is caused by a cascade of dysfunction from eating refined carbohydrate in the first place, and the other side is saying that fatness will occur regardless of the type of food eaten, and stresses that it’s more about the amount of energy taken in.


There’s truth to both angles. For instance, a given calorie of steak will have a different effect in the body than the same amount of sugar, broccoli, or butter. Although to be fair I haven’t encountered any respected proponent of the energy balance view who would dispute this.

But can we lay the blame of modern obesity mainly on refined carbohydrate? I suspect it’s more about the general environment.

Most people have unprecedented, unrestricted access to food—at least in the developed world. It’s ultra-convenient, cheap, and much of it is highly palatable, regardless of carbohydrate content or its degree of refinement. We’re constantly bombarded with advertisements from companies trying to jam their wares down our throats, and the term “obesogenic environment” is apt. High calorie food is everywhere and we don’t have to spend any energy through physical work to get it, which increases the likelihood of fat gain through the resulting positive energy balance.

It’s at least possible to remain very lean even with a high intake of sugar and other refined carbohydrate—I do it, and so do many others. Are we just outliers? Maybe. Conversely, it’s also quite possible to get extremely fat eating a lot of unrefined, unprocessed food (unfortunately I’ve also done this).

I’m also given pause by the fact that many cultures have traditionally eaten a lot of refined carbohydrate, and have remained lean and healthy. Was their particular food not sufficiently highly palatable and rewarding enough? I suppose it’s possible.

The Myths of Calories In vs Calories Out

The myths in this debate are mainly the ones erected in attempts to discredit the opposing side, and the heart of the debate really seems to be about obesity’s root cause.

Root causes are interesting academically, and are a necessary part of tackling obesity on a societal level. But if you’re in a bad way physically, how you got there is less important than fixing the problem.

We know that appropriate energy regulation (through diet and activity) will cut body fat. The focus for any overweight individual needs to be on finding a sustainable way to do this.

If you insist on believing that your insulin levels are to blame, no problem, don’t eat the refined carbs you think are causing it. It might help reduce your energy intake.

Cheers for reading, and there’s more on fat loss here.

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