The net energy values of the macronutrients in the diet are known as the Atwater general factors. A calorie (actually a kilogram calorie, kilocalorie or kcal) is a measure of heat used to express the energy contained in food. When the macronutrients are totally “burned up” in metabolism, they are broken down or oxidized. The amount of energy they liberate is in calories.
A few examples:
- 30 grams of carbohydrates or protein will provide 120 calories when metabolized (30 x 4 = 120).
- 30 grams of fat will release 270 calories (30 x 9 = 270).
