Carbohydrates are composed of units of carbon, hydrogen, and oxygen (commonly referred to as units of sugar) and are the body’s principle source of energy, providing about four calories per gram.
Most carbohydrates are eventually converted to glucose or glycogen in your body. Your central nervous system, including your brain, relies almost exclusively on glucose for fuel, and your muscles are powered primarily by glycogen during activity—two compelling reasons to make carbohydrate-rich foods a staple of your diet! In fact, 45% to 65% of your total calories should come from carbohydrates (in general, the more active you are, the more carbohydrate calories you require).
This macronutrient comes in two forms—simple and complex. Simple carbohydrates are those that consist of just one or two units of sugar. They are found naturally in fruit, fruit juices, and milk—all of which contain other important nutrients—and are added to many foods in processing. Table sugar, honey, syrups, candy, cookies, ice cream, fruit-flavored beverages, and colas are all examples of foods high in simple carbohydrates that provide calories but few additional nutrients.
Complex carbohydrates consist of many units of sugar and are often referred to as starches. Grain and plant foods such as cereals, pastas, rice, bread, crackers, potatoes, corn, and beans are all rich in complex carbohydrates as well as vitamins, minerals, water, and dietary fiber. Most of these foods are also naturally low in fat.