The following two options make sense mathematically and logically:

1. You consume as many calories as you burn. calories in = calories out. This would correlate with a healthy normal person.

2. You consume more calories than you expend. calories in > calories out. This would happen with an overweight person, who eats too much, junk food, beer, snacks.

If you persisted for an extended period of time in state 2 then you ought to balloon to 1000 pounds and die.

Probably the majority of overweight people don't become extremely obese and die from being extremely overweight.

That logically implies that after reaching some level of weight, they plateaued. Which means calories in = calories out.

This leads to two surprising conclusions.

1. In spite of the fact you see a person is fat, they are consistently eating a balanced diet: calories in = calories out. (sort of surprising, right?).

OR

1. In spite of the fact someone is fat, and eating too much, consistently, they are somehow not gaining weight from it, which is mathematically impossible.

How do you explain the situation of someone who is overweight, but then, maintains it. Would you agree they are probably eating a reasonable, even careful, balanced diet where calories in = calories out.

• Hardly hard to explain: your first alternative applies, with calories in roughly matching calories out for their current body and state (DeeV's answer says as much, perhaps less directly). Just like how income's equalling expenditure bears no particular connotation nor would it imply wealth or poverty. Commented Dec 19, 2023 at 3:36
• @Vandermonde, there could be a third explanation. After a certain weight level, the body determines that it has stored enough fat, and stops processing or storing additional calories. However, it may be that most (or all) organisms don't have such a mechanism as that.
– Sam
Commented Dec 19, 2023 at 12:57

How do you explain the situation of someone who is overweight, but then, maintains it.

This is based on the belief that a person's metabolism is static and never changes. This is false.

A person's metabolism increases as they gain weight. Being heavier means that it takes more energy to do the same things that it did previously.

The thermic effect of food or "TEF" also increases as food increases. This means that if you were to increase your diet by 500 calories, you're really increasing it by maybe 400 or so depending on the composition of the macronutrients. This effect gets bigger the more calories you eat.

Most people reach an equilibrium in which they are physically are unable to eat the amount of food that it would take for them to gain a significant amount of weight. So whether deliberate or not, they eventually reach a calories in = calories out scenario and plateau. Although a lot do not and will continuously outpace their metabolic gain.

Would you agree they are probably eating a reasonable, even careful, balanced diet where calories in = calories out.

It depends on what you're definition of a "reasonable" or "balanced" diet is. Just because you've reach an equilibrium doesn't mean the diet is particularly healthy or ideal.

• Thank you for the answer. TEF.
– Sam
Commented Jul 10, 2023 at 13:09

An energy-neutral, well balanced diet doesn’t mean much for Type-II diabetes and other comorbidities indicated by severe obesity.

The physics here is quite simple, and you’ve made the observation in your question: if you are weight stable, you are in energy balance. This is an entirely uncontroversial, indisputable fact. Your “surprising conclusion”, that “In spite of the fact you see a person is fat, they are consistently eating a balanced diet: calories in = calories out”, is not at all surprising, and shouldn’t be surprising to anyone with even the most basic knowledge of human metabolism.

But here’s the thing: it is also an uncontroversial, indisputable fact that when a person is severely obese, substantial and sustained reduction in adipose tissue is the number one way to reduce their risk of death due to diabetes, atherosclerotic cardiovascular disease, and a whole host of other complications caused by obesity.

Sure, there are weight-independent benefits of a well constructed energy-neutral dietary pattern, and transitioning to such a pattern is often an important step toward a dietary pattern that induces significant weight loss. But the fact remains that an energy neutral dietary pattern will not lead to weight loss, and is not going to do much for the risk of mortality associated with severe obesity.

I’m still not entirely sure what your question is, but I hope I’ve said something useful to you.

• "what your question is". Even I am not entirely sure what the question is. But I think that it's partly this: you have an overweight person, who is overweight due to consistently neglecting healthy diet choices. Yet they reach weight equilibrium, anyway. How is it explained? Probably, more frequently than not, they attain an equilibrium rather than becoming morbidly extremely obese and dying.
– Sam
Commented Jul 10, 2023 at 13:01