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Comment by ewindal | Hacker News Reader

You’re reading that wrong. Of course you burn more calories through exercise. Michael Phelps couldn’t have eaten 12k cals a day if exercise didn’t burn calories.

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Well that's what the article says. The Hazda who walk 8-12 km a day burn the less calories as an average American (or the same after adjusting for body weight).

Also that Phelps thing is highly questionable. He says he "probably" burns 8-10k, not 12k. Not the type of statement you want to rely on to dismiss all this work.

I just have a hard time believing it to be true that no amount of exercise will increase the overall caloric expenditure. For example, I've done a few multi-week bike tours, and we ate an enormous amount of mostly pasta every day, and managed to peel off a few pounds each by the end of it.

The article mentions a study that tracked energy expenditure of runners over many weeks, and found that the energy expenditure was much lower at the tail end of the experiment, suggesting the body gets accustomed to the activity somehow and burns less energy.

Well one obvious adaptation is losing fat = less energy needed to move the body.

We saw a very large reduction in caloric expenditure in people who were already very fit runners. So body weight changes over the course of the experiment are unlikely to explain it.

So if they just kept doing the experiment they would end up not needing to eat?

Clearly there are some details that matter here...

And in most places in the article calorie expenditure is taken as "corrected for no-fat weight".

The study must have tracked non-runners, given the conclusion. If they were already runners and the conclusion is that they get accustomed to the activity, they'd already be accustomed and there'd be no tail end difference. So they most likely tested non-runners and had them start running. We get more efficient at physical exertion with practice. Better coordination of muscle groups. Finding a more efficient pace. Correcting form deficiencies. These all increase capability or reduce energy expenditure.

This assumes that there isn't a spectrum of running intensity. In this case they were running 10s of kilometres every day during the study, an absurd distance. So they were likely experienced runners already who were engaging in this extreme competition and took it up to an abnormal intensity that they weren't used to.

It's strange. Go out in freezing weather and stand still;you'll get cold. Move about and you get warm. I find it unlikely that you can heat up without energy?

The article says pretty explicitly that, while you do burn more calories while exercising, your body finds other ways to compensate and generally keeps about the same total energy expenditure in a day.

I'm pretty sure this doesn't apply to extreme cases like modern athletes, who explicitly push their bodies in many ways that normal fit people don't, and who have teams of doctors and coaches that can force them to keep up with exercise and diet even when their bodies are telling them to stop.

Is it certain that we absorb all of the calories we consume? I went on a backpacking trip with my friends recently and despite similar activity levels everybody was surprised when they noticed that I eat twice as much as anybody else in the group.

Maybe I should bring it up with a doctor, but I feel fine, I just also spend more on food than most.

Yes, this. These conversations about weight loss are so rife with spherical cows and people come to ridiculous generalizations because of it. Bodies are complicated and varied. "Michael Phelps eats 12kcal a day and yet he's not fat" is just a correlation, it doesn't mean anything. He's an extreme outlier of a person in many ways.

I was eating similarly in my 20s and 30s and in 20s I kept about 80kg but in 30s I got to 130kg :/

BTW there are diseases that reduce calories absorbed, you might want to get checked for colitis ulcerosa and crohn's disease. They have nasty side effects so better to know earlier even if you don't have the worst symptoms.

No, there's lots of calories in stool, but it depends on the type of food. For example, eating lots of fats and oils tends to "go through". On the other hand, rate of metabolism varies between people too.

The body absorbs refined carbs very quickly. The glucose rush will increase insulin levels to very high levels and make you feel hungry again soon leading to the consumption of even more calories.

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