5 objections to the calorie deficit (and why none of them holds)

These sentences land in my comments under almost every post. "The deficit didn't work for me." "What about health problems?" "A calorie is not a calorie." "Surely it depends on hormones." "The body is an open system." None of these objections is stupid. Each one points at something that really exists. That still does not mean the deficit stops working.

Short answer: Yes, the calorie deficit still applies, even with hormones or a "slow metabolism". Health conditions, the thermic effect of food and hormones are real. They do not cancel the energy balance. They only change the numbers you put into it. In the Lichtman (1992) study, people who said they could not lose weight had underestimated their intake and overestimated their activity.

The five objections

1. "The deficit didn't work for me."
2. "What about health problems?"
3. "A calorie is not a calorie."
4. "It depends on hormones."
5. "The body is an open system."

Health conditions make fat loss harder. The thermic effect of food is real. Hormones move both sides of the equation. None of that makes the equation stop being true. It only changes the numbers in it. That is the whole difference between "it is hard to measure exactly" and "it does not apply".

Which of the five do you hear most? And which one makes you wonder if there is something to it?

Objection 1: "The deficit didn't work for me"

I know "calories decide" sounds like a tired fitness cliche. So for this one, here is the primary source.

Lichtman et al. (1992), published in the New England Journal of Medicine, looked at people who said weight loss just did not work for them. Their energy expenditure and their resting metabolism were within 5 % of the prediction. Their metabolism was not broken. The failure came from underestimated intake and overestimated activity.

That is the nuance the whole conclusion rests on. Nobody in that study had a body that ignored the balance. They had numbers that were off. More on why the "slow metabolism" story rarely holds is in the slow metabolism myth, and on how much movement really adds in cardio burns less than you think.

Objections 2 to 4: health, "a calorie is not a calorie", hormones

All three are real, and I am not going to pretend otherwise.

• Health problems can make fat loss harder.
• The thermic effect of food is real: digesting different foods costs the body a different amount of energy.
• Hormones move both sides of the equation, what comes in and what goes out.

But each of these changes a number in the balance. None of them removes the balance. You still lose fat when, over a longer stretch, you spend more energy than you take in. How to set that deficit is in calorie deficit: how much to eat.

Objection 5: "Thermodynamics only works for a closed system, and the body is open"

I hear this one again and again. It gets the physics backwards.

Conservation of energy holds for open systems too. You just have to count more flows: food coming in, heat, movement, breathing, what leaves the body. And it is exactly because the body is open that you can lose weight at all. Fat leaves it.

So this argument describes how the deficit works. It does not explain why it should fail.

What to take from it

When the deficit "does not work", the first suspect is not your metabolism. It is the numbers: how much you really eat and how much you really move. Check those before you look for an exception to physics. If you want a starting number, use the calculator.

Frequently asked questions

The deficit didn't work for me. Do I have a slow metabolism?

In the Lichtman (1992) study, people who said they could not lose weight had energy expenditure and resting metabolism within 5 % of the prediction. The failure came from underestimated intake and overestimated activity.

Doesn't thermodynamics only apply to a closed system?

No. Conservation of energy holds for open systems too. You just count more flows: food in, heat, movement, breathing, and what leaves the body. Because the body is open, you can lose weight at all. Fat leaves it.

What about hormones, health problems, and "a calorie is not a calorie"?

All of it exists. Health conditions make fat loss harder, the thermic effect of food is real, and hormones move both sides of the equation. The equation still holds. Only the numbers you put into it change.

Sources, so you can check:

1) Lichtman et al. (1992), New England Journal of Medicine. DOI: 10.1056/NEJM199212313272701

Martin Barna

Online nutrition and fitness coach. Since 2013 I have helped 600+ people lose fat and keep the result. Science, not crash diets.

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This article is for information only. It is not medical advice. If you have a health condition, talk to your doctor.