Chemical Energy in Foods
Food contains energy in the chemical bonds that hold the molecules (groups of atoms) together. The human digestive system breaks these bonds, releasing the chemical energy so that it can be converted into other forms.
Types of Energy
The process of breaking down organic matter to release the energy contained within it is known as respiration. Energy can be converted in mechanical energy, in the movements of the body’s muscles; electrical energy, in the function of the brain and the central nervous system; chemical energy, in the creation of new chemical bonds and hence new tissues; or thermal energy.
Sources of Chemical Energy
Food contains many different nutrients, but those that contain the most energy are lipids (fats), carbohydrates (molecules containing carbon, hydrogen and oxygen) and proteins (strings of amino acids). Energy is stored in the human body as the carbohydrate glycogen in the muscles and liver and in fat reserves.
Regardless of lifestyle, all human beings require a diet that is composed of roughly 55 percent carbohydrates, 30 percent lipids and 15 percent proteins.