Carbohydrates are the most important source of food energy. Starches are complex carbohydrates. They are found in such foods as grains, bread, peas and beans, and many fruits and vegetables. Sugars are simple carbohydrates. They are found in sweets and, to a lesser extent, in fruits and vegetables.

Most experts believe that complex carbohydrates are better for you than simple carbohydrates. This is partly because starchy foods also have many other nutrients, while sweets have few other nutrients. Also, there is some evidence that a lot of sugar in the diet may contribute to health problems.

Fiber is a carbohydrate called cellulose, which cannot be used by the body. Therefore, it supplies no food energy. However, it is important for the proper functioning of the digestive tract. Fruits and vegetables, especially if raw, and whole grains supply dietary fiber.

Fats supply energy to the body in highly concentrated form. Also, some fatty acids are necessary for regulating certain body functions. Third, fats act as carriers of fat-soluble vitamins, such as vitamins A, D, E, and K.

Fats may be classified as saturated and unsaturated. Saturated fats are solid at room temperature. Unsaturated fats, also know as oils, are liquid at room temperature. Health experts believe that unsaturated fats are more healthful and that and that saturated fats may contribute to heart disease.

Animal products — meats, poultry, fish, eggs, diary products — and solid shortenings are the major sources of saturated fats. Unsaturated fats are found mostly in vegetable products — nuts, whole grains, salad and cooking oils, and some fruits and vegetables.

Proteins are known as the building blocks of the body. They are essential for growth, for building body tissues, and for basic body function. They can also be used for energy if the diet does not contain enough carbohydrates and fat.

Proteins consist of substances called amino acids. The body is able to manufacture many of them, but there are eight amino acids that it cannot manufacture and must get from foods. A food protein that contains all eight essential amino acids is called a complete protein. Meats, poultry, fish, eggs and dairy products contain complete proteins.

Proteins that lack one or more of these essential amino acids are called incomplete proteins. Foods high in incomplete proteins include nuts, grains, dried beans and other legumes. Food which, if eaten together, supply all the amino acids, are called complementary proteins. For example, corn meal tortillas topped with chili beans supply complete protein, because the corn supplies the amino acids lacking in the beans. Beans and rice are another example of a combination that supplies complementary proteins.

Vitamins are present in foods in extremely small quantities, but they are essential for regulating body functions. Unlike proteins, fats, and carbohydrates, they supply no energy, but some of them must be present in order for energy to be utilized in the body. Also, lack of certain vitamins causes diseases called deficiency diseases.

Vitamins are classified as water-soluble and fat-soluble. The water-soluble vitamins (the B vitamins and vitamin C) are not stored in the body and must be eaten every day. Fat-soluble vitamins (A, D, E, and K) can be stored in the body, so they do not need to be eaten every day, as long as the total amount eaten over a period of time is sufficient.

Minerals, like vitamins, are also consumed in very small quantities and are essential for regulating certain body processes. The most important minerals in the diet are calcium, phosphorus, iron, copper, iodine, sodium, and potassium.

Sodium, a component of table salt, is somewhat of a health problem, not because we don't get enough of it, but because many people get too much. Too much sodium is thought to contribute to high blood pressure.

In order to maintain health, it is necessary to eat a variety of foods that will supply all the needed nutrients. The greater variety of foods we eat, the more likely we are to get all the nutrients we require.

A balanced diet every day is important for another reason. Nutrients work in teams, and all members of the team must be present at once in order for them to do their job. The United States Department of Agriculture recommends that individuals select foods from as many of the following groups as possible every day, in order to maintain a balance diet.