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."

If one of these is your story, the sections below are for you.

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

I know "calories decide" sounds like a tired fitness cliché.

Lichtman et al. (1992), published in the New England Journal of Medicine, looked at 10 people with obesity who said they ate under 1,200 kcal a day and still could not lose weight. Their energy expenditure and their resting metabolism were within 5% of the predicted value. Their metabolism worked as expected. The gap came from underestimated intake and overestimated activity.

It was a small study, so treat it as one piece of evidence. Still, in every one of them the gap came from numbers that were off, not from a body that ignored the balance. 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.

If you suspect a thyroid issue, PCOS or a medication that affects your weight, see your doctor and get tested. Do not change or stop any medication on your own.

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 the open system is exactly how the deficit works.

What to take from it

When the deficit "does not work", start with 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. If you have a history of disordered eating, do not start counting calories on your own. Talk to your doctor or a specialist first.

Frequently asked questions

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

Probably not. In the Lichtman (1992) study, a small group of people who said they could not lose weight had energy expenditure and resting metabolism within 5% of the predicted value. The gap came from underestimated intake and overestimated activity. If you have symptoms such as constant fatigue or feeling cold, ask your doctor for a thyroid test.

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. Some health conditions can 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 coached 600+ people through fat loss. Evidence-based coaching you can keep doing.

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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.