Food energy is defined as the energy released from carbohydrates, fats, proteins, and other organic compounds. When the three major calorigenic nutrients (carbohydrates, fats, and proteins) in a food are burnt entirely with sufficient amounts of oxygen, it releases energy or food calories that are expressed in kilojoules (kJ) or kilocalories (kcal). Food energy is usually measured by a bomb calorimeter based on the heat of combustion. Energy released by a particular food is a critical parameter in nutrition. Several chronic diseases such as obesity, diabetes, and cardiovascular disease have been considered to be caused by excess energy intake. All food manufacturers are now required to label the energy of their products to help consumers control their energy intake. Fats have the greatest amount of food energy per mass, up to 9 kcal g−1. Most of the carbohydrates and proteins have approximately 4 kcal g−1, whereas fibers have less due to its low digestibility and absorbance in human bodies. Restricting long-term consumption of high-energy foods rich in fats and sugar can reduce the incidence of obesity and other diseases.