Foods such as bread, cereal, rice, and pasta, as well as fruits and vegetables, are rich in sugars called carbohydrates. Carbohydrates are the major source of energy for cells. A healthful diet obtains up to 60% of its Calories from carbohydrate sources.
Carbohydrates are composed of carbon, hydrogen, and oxygen in the ratio Glucose is or Glucose is a simple sugar, or mono-saccharide, which consists of a single ring-shaped structure. Disaccharides Are two rings joined together—lactose, found in milk, is a disaccharide composed of glucose and galactose. The sugar you bake with or sprinkle on cereal is sucrose a disaccharide composed of glucose and fructose.
Joining many individual subunits, or monomers, together produces polymers (poly means “many”). Polymers of sugar monomers are called polysaccharides— these multi-subunit sugars can be composed of many different branching chains of sugar monomers and are also called complex carbohydrates.
Complex carbohydrates are often involved in storing energy for later use. Plants, such as potatoes, store their excess carbohydrates as polymers of starch. Animals store their excess carbohydrates as glycogen in muscles and the liver. Both starch and glycogen are polymers of glucose. Nutritionists recommend that carbohydrates in a healthful diet be mostly in the form of complex carbohydrates, and consumption of refined and processed sugars should be minimized. The complex carbohydrates you find in fruits, vegetables, and grains also contain many vitamins and minerals, as well as fiber—the refined sugars that you find in processed foods and sweets are a source of Calories, but do not supply vitamins, minerals, or fiber.
Dietary fiber, also called roughage, is composed mainly of complex carbohydrates that humans cannot digest into component monosaccharides. For this reason, dietary fiber is passed into the large intestine; some fiber is digested by bacteria living there, and the remainder gives bulk to the feces.
Although fiber is not digested, it is still an important part of a healthful diet. It lowers total cholesterol without changing the level of HDL, or “good” cholesterol while lowering LDL, the “bad”form of cholesterol-carrying molecules. Fiber may also decrease your risk of various cancers. Fruits and vegetables tend to be rich in dietary fiber.