• Fiber content. Fiber helps shield the carbohydrates in food from immediate digestion, so the sugars in fiber-rich foods tend to be absorbed into the bloodstream more slowly.
  
• Ripeness. A ripe fruit or vegetable has a higher sugar content than one that is still green and, therefore, has a higher glycemic index.
  
• Type of starch. The type of starch granules in a food influences how fast the carbohydrates are digested and absorbed into the bloodstream. The starch in potatoes, for example, is digested and absorbed into the bloodstream relatively quickly.
  
• Fat content and acid content. The higher a food's fat content or acid content, the slower its carbohydrates are converted to sugar and absorbed into the bloodstream.
  
• Physical form. Finely ground flour has a higher glycemic index than more coarsely ground flour.
  

Some foods that contain complex carbohydrates, such as potatoes, quickly raise blood sugar levels, while some foods that contain simple carbohydrates, such as whole fruit, raise blood sugar levels more slowly

Carbohydrates and the Glycemic Index

• High-glycemic
  
• Potatoes
  
• Bananas
  
• White bread
  
• White rice
  
• French fries
  
• Refined breakfast cereals
  
• White spaghetti
  
• Soft drinks
  
• Sugar
  

Low-glycemic

• Most Legumes
  
• Whole fruits
  
• Whole Wheat, Oats, Bran
  
• Brown rice
  
• Bulgar, Barley
  
• Whole grain breakfast cereals
  
• Couscous
  
  

Although the fine points of the glycemic index may seem complicated, the underlying message is fairly simple: whenever possible, you should replace highly processed grains, cereals, and sugars with minimally processed whole-grain products. And potatoes--once on the complex-carbohydrate, preferred list--should only be eaten occasionally because of their high glycemic index.

Popular Diets
A number of popular diets make carbohydrates one of their focal points. Some emphasize a high carbohydrate intake, while others emphasize a low intake. For more on weight control, see our healthy tips and lessons from loosers in our our Healthy Weight section.

High Carbohydrate/Very Low-Fat Diets
(For example, Dean Ornish, Pritikin, Food for Life Diet)

For years, you've probably heard the advice to cut back on the total amount of fat you eat and to consume more complex carbohydrates. And thousands of "low-fat" alternatives now crowd the supermarket shelves. But is simply cutting back on fat and loading up on carbohydrates a healthy way to eat or to lose weight? Current research suggests that it isn't. Just as researchers learned that not all types of fat are bad, they're also discovering that not all types of carbohydrates are good.

It's easy to fall into the "low-fat trap." Because fat, gram-for-gram, has more than twice as many calories as either protein or carbohydrates, it seems logical that choosing low-fat products would help with weight loss. However, all too often the low-fat products on supermarket shelves are packed with sugar to make up for the taste that's lost when fat is removed.

While people think that a low-fat alternative will hasten weight loss, it often has just as many calories as the full-fat version--and may even have more. In addition, many people mistakenly think that because a food is low in fat, they can eat as much of it as they want without gaining weight. But as far as the body is concerned, one calorie is the same as another, no matter where they came from. Eat too many calories (whether from fat, carbohydrates, or protein), and you'll gain weight.

Aside from weight loss, the popularity of low-fat food has broader implications for health. Many people are increasing the amount of carbohydrates in their diets, particularly in the form of sugars, and as we know from the discussion of the glycemic index, doing so may lead to increases in heart disease and diabetes.

For example, in a study of 80,000 nurses, Harvard researchers calculated that replacing a given number of calories from polyunsaturated fat with an equivalent number from carbohydrates increased the risk for heart disease by over 50 percent. And other studies have found that a low-fat, high-carbohydrate diet, particularly one high in sugars, can worsen blood cholesterol and triglycerides levels, both of which are risk factors for heart disease.

"Eat a low-fat diet," long the mantra of health and diet experts, has lost many adherents in recent years. Current research suggests that rather than focus on total fat intake, a healthier strategy is, first, to replace the "bad" fats (saturated and trans fats) with "good" fats (polyunsaturated and monounsaturated fats) and, second, to eat more whole grains high in dietary fiber. For weight loss, the best approach is to square the amount of food you eat with the number of calories you burn in a day. One of the best ways to lose weight or maintain a healthy weight is to exercise regularly. (For more information on dietary fat, click here.)

Low Carbohydrate, High Protein Diets
(For example, The Zone, Atkins diet, Gerald Reavan, and Protein Power Lifeplan)
In response to the potentially negative effects of a high-carbohydrate, low-fat diet, many books have been written on the potential benefits of a low-carbohydrate, high-protein diet. This approach often features types of food that most people avoid when trying to lose weight, for example, whole milk, steak, ham, and bacon. Although such diets are gaining in popularity, thus far only a few research studies have examined them or their underlying rationale. Although some initial results suggest that people can lose weight over the short term on a high-protein diet, this may simply be because they were consuming fewer calories, something that often happens when people drastically change what they eat. Whether a high-protein diet will actually maintain long-term weight loss still needs to be studied.

Apart from the uncertainty about its ability to maintain weight loss, the high-protein diet may have outright detrimental effects. Many of the high-protein foods that people choose while on this type of diet (red meat, cheese, and full-fat dairy products, for example) are high in saturated fat and low in vitamins and minerals. This may increase the risk for heart disease and colon cancer. Diets very high in protein (especially animal protein, like red meat) may also increase the risk for osteoporosis in women because the body takes calcium from the bone to neutralize the acids that build up in the blood as a result of digesting large amounts of protein.

Until more is known about the true risks and benefits of these low-carbohydrate, high-protein diets, they should be viewed with caution. Protein intake should be kept at moderate amounts (about 8 grams per day for every 20 pounds of body weight) and should be mainly vegetable protein. And carbohydrate-rich foods--in the form of whole grains, fruits, and vegetables--should still make up a large part of the diet.