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

It’s a matter of energy. When we eat, we absorb most of the nutrients and calories (a unit of energy) to use up and keep us functional. When we eat past how money calories our body needs to use in a day, those calories get saved as fat. Fat serves a few purposes. 1. It insulates us and helps regulate our temperature so we don’t burn through our energy faster. 2. If we under eat in a day, our bodies will use those stored calories as energy instead