In terms of weight gain, a calorie is a calorie is a calorie. Calories not used immediately by your body for energy are either eliminated as waste or stored as fat. YOU-reka! But that doesn’t mean that all calories are treated equally by your body. For example, protein and fiber with high water content have a great effect on satiety, and simple carbohydrates have the least effect on satiety. (Fat, by the way, has an effect on satiety similar to that of protein and fiber, which is why low-fat diets leave people hungry all the time.) When it comes to converting calories, your body processes fat most efficiently—meaning that you actually keep more of it, because your body doesn’t need to expend as many calories trying to store it. On the flip side, your body works hard to process protein, to make it highly flammable to your body’s metabolic furnace.