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Comment by cercatrova | Hacker News Reader

Obesity and weight gain in general is mainly caused by diet, not exercise. You can run 12 hours a day but if you eat 10k calories a day, you're going to end up fat.

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I think the mainly part is correct, but 12 hours of running like 6-7k calories for an 150 lbs. person. As you get heavier it’s going to go up fast (and non linearly)—essentially any kind of extreme exercise is going to put an upper limit on your weight.

I’m unsure if your body can even process 10k calories in day. The basal metabolic rate for a 1000 lbs person isn’t that high.

They were making a point with an exaggerated example, not suggesting that 12 hours of running or 10k calories/day is actually reasonable.

I never said that the OP implied it was reasonable. My point is that there's a level of activity at which you likely can't eat enough to get fat.

Michael Phelps is probably the only most valid extreme example!

https://olympics.com/en/featured-news/michael-phelps-10000-c...

Lots of ultra distance runners and cyclists eat and burn more than that. The point is with sufficient exercise it is almost impossible to stay fat.

And the counterpoint is that most people aren't able to do that much exercise. Because it's A LOT. Basically full time athletes or highly physical workers. So that excludes all people with a sedentary or only partially physically demanding work.

Sufficient is a lot. If you eat a fast food meal (burger, fries, soda) above maintenance you're looking at half a marathon to burn that off. And most people aren't pro cyclists that are able to sustain 400 watts+ for a hour.

Sufficient is a lot, but it’s nowhere near as extreme as that example makes it sound.

That’s a half marathon for a 150 lbs fit person, running efficiently. A 250 lbs person who is a little out of shape will burn that in a 2.5 hour walk.

Obviously 1300 calories a day above maintenance is extreme for most people, but energy expended scales non linearly with weight. There are also a lot quicker ways to burn calories than marathon running.

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