Most of the nutrients in foods belong to one of five classifications: the macronutrients, which are proteins, carbohydrates and fats, or the micronutrients, which are vitamins and minerals. These and water provide you with most of your daily nourishment.
Protein is an energy source, but its primary functions are to build and repair the tissues of the body and to help fight infection. The body only uses protein for energy if you consume more than your body needs to perform the other two functions. Protein food sources include meat, poultry, seafood, eggs, dairy, nuts and legumes. Proteins are made of amino acids, of which only 20 exist in nature.
Carbohydrates provide most of your energy, with 4 calories per gram. Carbohydrates are formed by chains of sugar, or glucose, and are classified as simple or complex,depending on how long these chains are. Complex carbohydrate foods include breads, whole grains, rice, cereals, pasta and starches such as potatoes and corn. Whole-grain carbohydrates are also sources of dietary fiber. Simple carbohydrates include sugar, fruit, candy, sodas, honey and syrups.
Fats provide the body its most concentrated source of energy, at 9 calories per gram. Any fat the body doesn't burn for immediate energy, it stores for later use. Fats help the body absorb fat-soluble vitamins from the diet, including vitamins A, E, D and K. Food sources of fats include oils, margarine, shortening and salad dressings. Animals products, including meat and dairy, also contain fats. There are three types of fats: unsaturated, saturated and transfats. Unsaturated fats can provide several health benefits, including improving cholesterol levels. However, saturated fats elevate LDL, or "bad" cholesterol, levels. According to the Harvard School of Public Health, the body can produce all the saturated fat we need, so we don't really need any from our diet. Transfats form when vegetable oils are heated to the point of hardening; these are found mostly in fried and processed foods. They are the unhealthiest of the three types of fat because they not only raise LDL levels but lower HDL or "good" cholesterol levels as well.
Vitamins are compounds your body needs for proper growth and development. According to the National Institutes of Health, the body requires 13 different vitamins, most of which must come from the diet. These 13 essential vitamins are vitamins A, E, C, D, K and the eight B-complex vitamins: thiamine, riboflavin, niacin, folate, biotin, pantothenic acid, B-6 or pyridoxine and B-12. Different vitamins can be found in varying proportions in most natural foods. Fruits and vegetables in particular are high in vitamins. Different vitamins are associated with different health effects. For example, vitamin A helps keep eyes, skin and mucus membranes healthy and promotes growth; vitamin C helps the body absorb iron and resist infection; and vitamin D helps the body absorb calcium and build strong teeth and bones.
Like vitamins, different minerals are associated with different health benefits. For example, calcium and phosphorous help build strong bones, and magnesium helps the body utilize energy from proteins, fats and carbohydrates. What distinguishes minerals from vitamins is that minerals cannot be made by living organisms such as plants; instead, they come from non-living sources such as the soil, rocks and water. In fact, the plants that make vitamins draw the minerals they need for their life processes from the soil. Other minerals important for the human diet include potassium, iron, copper, zinc, iodine and manganese. Food sources of minerals vary widely, depending on the mineral.