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

Calorie count is a good approximation of how much energy is available to your body from food. Your body is going to do one of two things with energy: use it or store it. You are only going to use the exact amount of energy you need during the day, anything above that is going to be stored. You get calories from three different sources: carbohydrates, fat, and protein. The calorie density for each of these are different, fat is 9 Cal/gram while carbs and protein are 4 Cal/gram each. Finally, there are parts of food that cannot be used and just pass through your system.