Fiber is made up of complex carbohydrates that are not a source of energy and are generally not completely digested before passing through the body. There are two different types: insoluble fiber and soluble fiber. Most plant foods contain varying amounts of both types.

Uses

Insoluble fiber, such as cellulose, hemicellulose and lignin -- found in whole grains and other plants -- are natural laxatives. They absorb water, help you feel full after eating and stimulate your intestinal walls to contract and relax. By moving food quickly through your intestines, insoluble fiber may help prevent or relieve digestive disorders such as constipation or diverticulosis (infection caused by food getting stuck in small pouches in the wall of your colon). Insoluble fiber also makes your stool softer, relieving or reducing your risk of hemorrhoids.

Soluble fiber, such as pectin (found in apples) and beta-glucans (found in oats and barley) may lower your cholesterol level, and may be a factor in explaining why a diet rich in fiber seems to offer some protection against heart disease.

Sources

Fiber is found in all plant foods -- fruits, vegetables and grains. But there is no fiber in animal foods -- meat, fish, foul, eggs and dairy.

Recommended intake

According to the US Department of Agriculture, the average American woman gets about 12 grams of fiber per day and the average man gets about 17. That's well below the current recommendations, which is 20 to 30 grams per day.

The majority of calories in your diet come from starches, or complex carbohydrates. Unlike simple sugars, complex carbohydrates consist of long chains of sugar units linked together. Before they can be absorbed, these sugars must be split apart, and this means they are more gradually absorbed into the bloodstream.

Uses

Complex carbohydrates provide a lasting source of energy. This is particularly important for athletes fueling up for an event. Because carbohydrates yield only four calories per gram, they are essential to any weight control program. This idea runs counter to earlier theories about dieting, where the first things to get ousted from the diet were those "fattening" starchy foods. High carbohydrate foods are actually low in fat -- unless you add fat in cooking or at the table.

Sources

Starches are found in foods like breads, cereals, starchy vegetables, legumes, rice and pasta.

Recommended intake

The current Dietary Guidelines for Americans, produced by the US Departments of Agriculture and Health and Human Services, suggest 6 to 11 servings a day of grain foods (bread, cereal, pasta, rice) plus 3 to 5 servings of vegetables and 2 to 4 servings of legumes -- which all contain complex carbohydrates.

Sugars, or simple carbohydrates, are divided into two groups: monosaccharides (glucose, fructose and galactose) and disaccharides (sucrose, lactose, maltose). Most sugars have one appealing trait in common -- sweetness. Simple sugars provide calories but not many vitamins and minerals. With its minimal nutrient contribution, sugar has been blamed for everything from obesity to hyperactivity. But the only disorder sugar has been directly linked to is tooth decay. As long as you're getting your sugar from an apple and not a candy bar, there is no harm in including it in your diet.

Uses

Carbohydrates, along with proteins and fats, provide the energy we need from our diets. In fact, carbohydrates provide most of the calories your body uses. Nutritious sources of sugar will provide an easily available source of energy.

Sources

Sugars are found in all types of foods, such as milk and milk products, fruits and vegetables. They are also found in sweet-tasting processed and refined food products, such as candy, honey, syrups and carbonated beverages.

Recommended intake

The current Dietary Guidelines for Americans, produced by the US Departments of Agriculture and Health and Human Services recommends getting to 2 to 4 servings of fruit and 3 to 5 servings of vegetables per day -- both nutritious sources of simple carbohydrates. Refined sugars are only recommended on a once-in-a-while basis.