• Complex carbohydrates, which are chains of simple sugars, consist primarily of starches as well as the fiber that occurs in all plant foods. Starch is the storage form of carbohydrates in plants. Foods rich in complex carbs include grains and grain products (such as bread and pasta), beans, potatoes, corn, and some other vegetables.

Are complex Carbs preferable to sugars?

Yes, usually. Many foods high in sugar (especially sucrose and other added sugars) supply "empty calories"—that is, they have few nutrients but lots of calories. By contrast, the calories in foods rich in complex carbs usually bring many nutritional extras with them. It depends on the food. Dairy products and fruit contain sugars, but are important parts of a healthy diet because of the other nutrients they contain.

Some foods rich in complex carbs are better than others. White bread and french fries contain complex carbs, for instance, but you can make better choices. Whole grains (such as oats, whole wheat, brown rice) are more nutritious than refined grains, since they retain the bran and the germ, which are rich in vitamins, minerals, fiber, and beneficial phytochemicals. Whole grains are digested more slowly, and thus have a more modest effect on blood sugar than refined carbs or sugars (see below). The same is true of vegetables and beans. The fiber in these foods has many health benefits. In particular, soluble fiber (found in oats, barley, and beans) may help lower LDL ("bad") cholesterol, triglycerides, and blood pressure. In fact, people whose diet is rich in whole grains and other high-fiber foods tend to have a lower risk of heart disease, diabetes, and some cancers.

The glycemic index

Various high-carbohydrate foods have different effects on blood sugar. This effect is measured by the "glycemic index," which is mentioned in many of today's diet books. The index indicates how fast a food is digested into glucose and absorbed, and thus how much it causes blood glucose to rise. Some studies suggest that a diet rich in foods high on the glycemic index (meaning they have a strong effect on blood sugar) increases the risk of diabetes, at least in those pre-disposed to it, and lowers HDL ("good") cholesterol.

The index doesn't merely reflect whether the carbohydrates in a food are simple or complex. Many factors come into play, including the amount of fiber and fat in the food, how refined the ingredients are, and whether the food was cooked. Table sugar and honey are high on the glycemic index. But so are raisins, corn, potatoes, carrots, watermelon, doughnuts, white bread, instant rice, and most breakfast cereals. Apples, peaches, and ice cream, as well as most beans, grapefruit, and peanuts, are low on the index. Pasta is in the middle.

The glycemic index has little practical use, however. You shouldn't try to build your diet around it, as some well-known diet doctors (including Dr. Atkins) advise. The main problem: it deals with single foods eaten by themselves. Potatoes may be high on the index, but when eaten as part of a meal, they have much less of an effect on blood sugar. There is no reason to avoid foods high on the glycemic index—many are very nutritious. Even people predisposed to diabetes, or with the disease, can eat these foods in moderation.