Results

Weight loss
Commercial diets that are based on the glycemic index say that you'll lose weight without having to count carbs or calories. Foods that have a low glycemic index ranking are said to make you feel full longer and to balance your blood sugar.

Results from research studies are mixed, and some studies have been of poor quality. Some studies show that calorie for calorie, there's little difference in hunger after eating a high GI food or a low GI food. Other studies, though, conclude that you're more likely to lose weight and reduce your body mass index (BMI) with a glycemic index diet than with a traditional diet, even if you're obese and need to lose a significant amount of weight. That may be, at least in part, because it's easier to stick to the glycemic index diet for the long term since it's not considered an extreme diet.

One study showed that participants following the Zone diet maintained a weight loss of about 7 pounds (3.2 kilograms) after one year — about the same amount of weight lost as in the three other diets in the study. There have been few studies about the impact of the glycemic index diet on weight loss after a year or more. But some evidence suggests that a diet higher in protein and lower on the glycemic index may lead to sustained weight loss. Some evidence also suggests that you may lose weight on a glycemic index diet simply because you choose more fiber and protein, which helps you reduce portion sizes and eat less.

Still other studies suggest that there's little if any evidence that having an elevated blood sugar level leads to weight gain if you're healthy. These studies note that insulin is vital to good health, and that insulin becomes a problem only when insulin resistance develops. Insulin resistance doesn't develop from eating certain carbs or proteins but from being overweight. Weight loss from any type of diet improves blood sugar control.

The bottom line is that to lose weight, you must reduce the calories you take in and increase the calories you burn. Traditional recommendations for weight loss advise losing 1 to 2 pounds (0.45 to 0.9 kilograms) a week by reducing calories and fat and emphasizing complex carbohydrates. Losing a large amount of weight rapidly could indicate that you're losing water weight or lean tissue, rather than fat.

Health benefits
Proponents of the glycemic index diet say that you can improve or reduce the risk of serious diseases, including diabetes and cardiovascular disease.

Almost any diet can reduce or even reverse risks factors for diabetes and cardiovascular disease — if it helps you shed excess weight. And most weight-loss diets can improve blood cholesterol or blood sugar levels, at least temporarily.

On the other hand, the glycemic index doesn't rank foods according to how healthy they actually are. Indeed, some foods with the preferred lower GI ranking may, in fact, be less healthy because they contain large amounts of calories, sugar or saturated fat, especially packaged and processed foods. Both potato chips and ice cream, for instance, have a lower glycemic index ranking than do baked potatoes, even though baked potatoes are generally considered healthier. So while lower GI items may help blood sugar balance, choosing them indiscriminately could lead to other health problems.

Other concerns
One major concern with the glycemic index is that it ranks foods in isolation. But in reality, how your body absorbs and handles carbs depends on many factors, including how much you eat; how the food is ripened, processed or prepared; the time of day it's eaten; other foods you eat it with; and health conditions you may have, such as diabetes. So the glycemic index may not give an accurate picture of how one particular food affects your blood sugar. Glycemic load is a related concept that scores a food product based on both carb content and portion size. But the larger the portion size, the greater the calories consumed whether the glycemic index is high or low.

It also can be difficult to follow a glycemic index diet on your own. For one thing, most foods aren't ranked by glycemic index. Packaged foods don't generally list their GI rank on the label, and it can be hard to estimate what it might be. And for some types of food, the glycemic index database has multiple entries — you may not be sure which entry is accurate.

On the other hand, many generally healthy foods are naturally low on the glycemic index, such as whole grains, legumes, vegetables, fruits and dairy products. If you eat a healthy diet, based on fresh foods that aren't highly processed, you may get the same benefits of the glycemic index diet. But if you need extra guidance toward healthier choices, the glycemic index may help.

Risks

Studies of the glycemic index diet haven't revealed any specific health risks to following the diet. However, it's possible that if you choose lots of low GI foods that are high in calories, sugar and saturated fats, you could develop some of the same health problems the diet hopes to prevent.

Aug. 24, 2011 See more In-depth