Your body stores excess energy as fat, or uses it to build muscle. The amount of food mass in your body at any given time is assumed to be constant in the long

Your body stores excess energy as fat, or uses it to build muscle. The amount of food mass in your body at any given time is assumed to be constant in the long term, so when we talk about a person's weight changing we are generally referring to a change in their fat or muscle mass. 1kg of ice cream has a much greater potential to change your long-term mass than 1kg of broccoli because your body has the ability to extract more energy from it, and thus build more fat or muscle.