Fats also serve as solvents for hormones and fat-soluble vitamins. 3. Carbohydrates – form the major part of stored food in the body for later use of energy. Glucose which is a monosaccharide is the body’s primary source of energy. When in excess, it is stored in the liver as Glycogen. Carbohydrates are also important for fat oxidation and can also be converted into protein.