Why is it the calorie count of food, and not the mass, that determines weight gain?

Question

Why is it the calorie count of food, and not the mass, that determines weight gain?

In: 2

Answer 1

Food, no matter the quantity by mass, will be broken down in your body into the parts that your body can use to make energy. Energy is what your body is after. Since everything will ultimately get turned into energy (/energy-storing molecules like fat), this is why calories (a unit of energy as it’s used by the body) is what contributes to weight gain.