Carbohydrates are the body's main source of energy. In food, car­bohydrates can be sugars or starches. But in the body, both types are converted into glucose (blood sugar), the fuel we use to do everything from breathe to run a marathon.

Sugars, like the carbohydrate in fruit or table sugar, arc made up of only one or two sugar units. Starches, however, are made up of many sugar units. They're not sweet because their molecules are too big for our taste buds to detect. (If you leave a cracker in your mouth long enough for the digestive enzymes in your saliva to break down the starch into sugar, you'll taste sweetness.)

So if all carbohydrates eventually become glucose in the body, does it make any difference if we get our carbohydrates from sugar or from starch? Yes, in fact, it makes a big difference. Prepared foods containing simple sugars tend to contain a lot of fat and calo­ries and are usually low in vitamins and minerals. In other words, they're not nutrient dense. A number of starchy foods, however, are rich in micronutrients and in the case of beans and legumes, rich in protein as well. Fruits, although they contain the sugar fruc­tose, also are rich in fiber and lots of vitamins. Some foods—whole-grain breads, rice, pasta, beans and vegetables—are good sources of both starch and fiber.