I understand a calorie to mean a certain measurement of energy produced when food is processed by the body. There are certainly different types of food, proteins, carbs etc. But the measurement unit of a calorie can't change. It's like saying there are different types of degrees Centigrade. Fats, for example, are high in calorific content, but they're the same units of measurement as the far fewer calories in, say, lemon juice. The more calories left over after energy is exerted, the more are stored as fat in the body. If one ate tons and tons of a low-calorie food, one would still get fat. If one ate only a tiny lump of, say, lard, every day, one would still get thinner and thinner.