eli5: how does weight gain work?

Question

Is it a matter of in/out? In other words, eat a pound of food, eliminate 8oz of waste, gain 8oz? If not, why not?

In: 1

Answer 1

Not quite. Depends on how much breathing you do before you weigh yourself. Regardless of what that food you just ate is doing, you’re burning the energy gathered from the food you’ve eaten before. That process releases water which you may also urinate, sweat, or breathe out and carbon dioxide when you’re pretty consistently exhaling.

You lose weight breathing as you sleep.