The products of digestion are used to build new carbohydrates, lipids, and proteins. Specifically, glucose from carbohydrate digestion can be used to form new carbohydrates like glycogen. Amino acids from protein digestion are used to build new proteins, and fatty acids and glycerol from lipid digestion are used to build new fats and lipids. These substances are essential for cell function and growth, including forming cell membranes and hormones. Additionally, some glucose is used for cellular respiration to release energy.