The term calorie (kcal) refers to the amount of energy that food provides to the body as long as it is fully utilized. Based on this, we can compare the energy provided by carbohydrates, proteins and fats by the percentage of calories each has.
Carbohydrates are approximately 4.0 kcal, regardless of source. For this reason they are a great source of energy, managing to meet the needs of the body. In proteins, we often find the value of 4.0 kcal too, because proteins provide energy like carbohydrates, but at a higher cost to the body with respect to the amount of energy needed for metabolism (protein burning). Fats, in turn, have about 9.0 kcal, being the largest source of energy among the three molecules.
