The Glycemic Index Diet (Low Glycemic Diet)

What It Is

The "glycemic index diet," "GI diet," and "low glycemic diet" are more than diet books. They refer to a system of ranking carbohydrate foods according to how much a certain amount of each food raises a person's blood sugar levels.

Originally developed as a tool to help diabetics manage blood sugar control, the glycemic index has found its way into the mainstream weight loss market. The glycemic index is the basis for many popular diet plans, such as SouthBeach, The Zone, Sugar Busters, Glucose Revolution, and Ending the Food Fight. 

Specifically, the glycemic index (GI) measures how much a 50-gram portion of carbohydrate raises a person's blood-sugar levels compared with a control (that is, white bread or pure glucose). Virtually all carbs are digested into glucose and cause a temporary rise in blood glucose levels, called the glycemic response. This response is affected by many factors, including the quantity of food; the amount and type of carbohydrate; the cooking method; degree of processing, and more. Each food is assigned an index number from 1-100, with 100 as the reference score for pure glucose. Typically, foods are rated high (greater than 70), low (less than 55) or moderate (56-69).

The glycemic index diet's popularity has been fueled by claims that low-GI foods can help control appetite and weight and may be useful for people with diabetes or pre-diabetes. The idea is that low-GI foods are absorbed more slowly, allowing dieters to feel full longer and making them less likely to overeat. 

Dieters are encouraged to choose carbohydrate foods with a low glycemic index, which tend to be (but are not necessarily) healthier, nutrient-rich, less refined, and higher in fiber -- like whole fruits, vegetables, and beans.

In contrast, higher GI foods "trigger a rise in blood sugar, followed by a cascade of hormonal changes, which tend to make you hungry again sooner because they are metabolized quicker than low-GI foods," explains David Ludwig, MD, PhD, author of Ending the Food Fight.

The blood sugar spikes of high-GI foods are especially problematic for people with diabetes because their bodies have trouble regulating blood sugar. The theory that helped launch all the glycemic index diets is this: If it works to help control blood sugar in diabetic people, then it should work for weight control.

Because the GI diet is an approach to weight loss rather than a specific plan, guidance on fats, protein, alcohol, weight maintenance and exercise vary depending on the plan. Ludwig and most GI diet plans also advocate getting regular exercise and eating moderate amounts of lean protein and healthy fats -- similar to the recommendations of the U.S. government's 2005 Dietary Guidelines.

What You Can Eat

Quality, not quantity, of carbs is the mantra of a glycemic index diet. The idea is to feel fuller by enjoying plenty of low-GI "smart" carbs -- whole grains, whole fruits, vegetables and legumes -- along with lean protein and healthy fats. You'll avoid the high GI foods, which tend to be made with white flour and heavily processed.