Humans historically ate to support activity due to food scarcity, whereas today activity supports eating, and one cannot out-exercise their caloric intake.

“So, where I'm going with metabolism is that all the discussions we have about metabolism, about boosting metabolism, about all these things, even cold stress, a lot of them fall into that simple thing I said earlier, which is we use to eat to support our activity because food was rare. And today, we're active to support our eating. And the more simple thing is you can't out exercise your mouth. It's impossible. It's thermodynamically impossible. You can swallow way more than you can move. It's just not...”