324 Chapter 13 Nutrition Copyright Goodheart-Willcox Co., Inc. Carbohydrates Carbohydrates are the major sources of energy in your diet. There are three kinds of carbohydrates: sugars, starches, and fi ber. Your body can change both sugars and starches into energy. Sugars are simple carbohydrates, 13-1. Your body can use some sugars right away for energy. Other sugars must fi rst be broken down into simpler sugars. Starches are often called complex carbohydrates. Before your body can use starches for energy, it must convert the starches into simple sugars during digestion. Nutrition experts recommend most people get more than half of all their daily calories from complex carbohydrates. (People who are diabetic must monitor their carbohydrate intake and follow a prescribed diet.) Like starch, fi ber is a complex carbohydrate. Although your body cannot digest fi ber, you need fi ber in your diet. This is because fi ber provides roughage that stimulates the normal activity of your intestines. Fiber moves food through your body and helps your body get rid of solid wastes. When you eat more carbohydrates than your body can use, some of them are changed to glycogen. Glycogen is stored in your body for times when you need quick energy, such as when you run to catch a bus. Your body maintains only a small amount of glycogen. Excess carbohydrates that are not stored as glycogen are changed to fat for storage in the body. Proteins Proteins are a nutrient found in every cell in your body. They are needed for growth, maintenance, and repair of body tissues. Proteins are made up of amino acids, which are building blocks for your cells. Not all protein sources are the same. There are two classes of proteins—complete proteins and incomplete proteins. Complete proteins supply all the amino acids your body needs. Foods that come from animals are sources of complete proteins. Incomplete protein sources contain some, but not all, of the amino acids your body needs. Few plant sources provide complete proteins. People whose diets are low in protein experience poor muscle tone, lack of energy, and reduced resistance to disease. Severe protein shortages may result in a disease called kwashiorkor. Protein consumed beyond the body’s needs is stored in the body as fat. 13-1 Milk and cookies are both sources of simple carbohydrates.