Carbohydrates Carbohydrates provide the major source of energy for the body. RDA is about 50 to 65 percent carbohydrates. Major sources of carbohydrates are cereals, fruits, breads, and some vegetables. Each gram of carbohydrate contains four Calories. There are two types of carbohydrates: Simple carbohydrates are used for quick, immediate energy. Complex carbohydrates are used to supply long-lasting energy.

Fats Fats (lipids) are another major energy supply for the body. Each gram of fat contains nine Calories. RDA is to consume no more than 30 percent of their daily intake of Calories from fat. There are two types of fatty acids found in lipids: Saturated fatty acids are found mostly in animal fat such as meats and cheese. Generally, they are solid or semi-solid at room temperature. Unsaturated fatty acids are found mostly in plant oils. They form fats that are liquid at room temperature.

Protein Proteins serve to build and repair body tissue and make hormones within the immune system that help to fight off infections. They also form parts of muscle, hair, skin, nails, connective tissue, and glands. Proteins can also serve as a source of energy. Each gram of protein has 4 Calories. Ten to fifteen percent of food intake should come from protein. Meats, fish, legumes, nuts, eggs and dairy products are major sources of protein.

Vitamins Vitamins are compounds that allow many of the chemical processes in the body to occur. Vitamins themselves provide no energy to the body; however, without vitamins, the cells would not be able to carry out chemical reactions that permit the body to function properly. 13 different vitamins are essential for health. They are placed in one of two groups: Fat-soluble vitamins dissolve in fat. The four fat-soluble vitamins are D, K, A and E. Water-soluble vitamins dissolve in water. There are nine water-soluble vitamins, including the B vitamins and vitamin C.

Minerals Minerals are natural substances found in the earth's crust. They play many different roles such as: regulating blood pressure, facilitating muscle contraction, providing major components of bones, healing wounds, and help in conducting nerve impulses. Minerals are found in a variety of foods. There are two classifications of minerals in the human body, both of which are important to proper body function. Minor elements (only in small amounts): includes iron, copper, fluorine, iodine, selenium, zinc, chromium, cobalt, manganese, and molybdenum. Major elements (large quantities): includes calcium, potassium, sodium, magnesium, phosphorus, chloride, and sulfur.

Water Water makes up about 50 to 60 percent of the body's weight. Water is crucial to survival. Every cell in the body must have water in order to survive. An adult can survive about eight weeks without food but only a few days without water. Water's important functions include: It is the perfect medium for all of the chemical reactions to occur. Water helps regulate body temperature-heating and cooling the body. Water helps remove waste products from the body. Water controls the concentration of nutrients in the body. Water aids the digestive and respiratory processes.