Diet details

A GI diet prescribes meals primarily of foods that have low values. Examples of foods with low, middle and high GI values include the following:

  • Low GI: Green vegetables, most fruits, raw carrots, kidney beans, chickpeas, lentils and bran breakfast cereals
  • Medium GI: Sweet corn, bananas, raw pineapple, raisins, oat breakfast cereals, and multigrain, oat bran or rye bread
  • High: White rice, white bread and potatoes

Commercial GI diets may describe foods as having slow carbs or fast carbs. In general, foods with a low GI value are digested and absorbed relatively slowly, and those with high values are absorbed quickly.

Commercial GI diets have varying recommendations for portion size, as well as protein and fat consumption.

Results

Studies of the benefits of GI diets have produced mixed results.

Weight loss

In a 2013 review of 23 published clinical trials of low-GI or low-GL diets, researchers concluded that the diets were "as effective as other dietary alternatives in inducing weight loss." In four of the studies, low-GI or low-GL diets resulted in statistically significant improvements in weight loss when compared with other diets. Ten studies showed a slight improvement — but not a statistically significant improvement — in weight loss.

In another 2013 review, researchers analyzed clinical trials that compared two or more specialty diets to various dietary guidelines, including those published by the American Diabetes Association and the European Association for the Study of Diabetes. The results showed that low-carbohydrate diets and Mediterranean diets provided more weight-loss benefit than low-GI diets. (A Mediterranean diet includes olive oil, legumes, whole-grain cereals, fruit, vegetables, and modest amounts of meat and dairy products.)

A large trial published in 2010 followed 773 participants who had lost weight on a low-calorie diet. During the six months following this weight loss, people who ate a low-GI, high-protein diet were more likely to stick with their diet plan and not regain the weight they had lost.

Blood glucose control

A treatment goal for people with diabetes is to keep after-eating and average blood glucose levels as close to nondiabetic levels as possible. This tight control helps prevent or slow the development of complications associated with the disease.

Some clinical studies have shown that a low-GI diet may help people with diabetes control blood glucose levels, although the observed effects may also be attributed to low-calorie, high-fiber content of the diets prescribed in the study.

Cholesterol

Reviews of trials measuring the impact of low-GI index diets on cholesterol have shown fairly consistent evidence that such diets may help lower total cholesterol, as well as low-density lipoproteins (the "bad" cholesterol) — especially when a low-GI diet is combined with an increase in dietary fiber.

Appetite control

One theory about the effect of a low-GI diet is appetite control. The thinking is that high-GI food causes a rapid increase in blood glucose, a rapid insulin response and a subsequent rapid return to feeling hungry. Low-GI foods would, in turn, delay feelings of hunger. Clinical investigations of this theory have produced mixed results.

Also, if a low-GI diet suppresses appetite, the long-term effect should be that such a diet would result over the long term in people choosing to eat less and better manage their weight. The long-term clinical research does not, however, demonstrate this effect.

The bottom line

In order for you to maintain your current weight, you need to burn as many calories as you consume. To lose weight, you need to burn more calories than you consume. Weight loss is best done with a combination of reducing calories in your diet and increasing your physical activity and exercise.

Selecting foods based on a glycemic index or glycemic load value may help you manage your weight because many foods that should be included in a well-balanced, low-fat, healthy diet with minimally processed foods — whole-grain products, fruits, vegetables and low-fat dairy products — have low GI values.

For some people, a commercial low-GI diet may provide needed direction to help them make better choices for a healthy diet plan. The researchers who maintain the GI database caution, however, that the "glycemic index should not be used in isolation" and that other nutritional factors — calories, fat, fiber, vitamins and other nutrients — should be considered.

Sep. 25, 2014 See more In-depth