Proteins are often called the body’s building blocks. They are used to build and repair tissues. They help you fight infection. Your body uses extra protein for energy. Carbohydrates are the body’s main source of energy. There are two types of carbohydrates: simple and complex. Fats also give you energy and help you feel satisfied after eating. There are different categories of fats—some are healthier than others. Water keeps your body temp. in check, lubricates your joints, protects your spinal cord, and rehighrates your body.