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 GI: 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

Depending on your health goals, studies of the benefits of GI diets have produced mixed results.

Weight loss

Results of a 16-year study that tracked the diets of 120,000 men and women were published in 2015. Researchers found that diets with a high GL from eating refined grains, starches and sugars were associated with more weight gain.

Other studies show that a low GI diet may also promote weight loss and help maintain weight loss. However, data from another study indicated a substantial range in individual GI values for the same foods. This range of variability in GI values makes for an unreliable guide when determining food choices.

Blood glucose control

Studies show that the total amount of carbohydrate in food is generally a stronger predictor of blood glucose response than the GI. Based on the research, for most people with diabetes, the best tool for managing blood glucose is carbohydrate counting.

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 the 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. Low- to moderate-GI foods such as fruits, vegetables and whole grains are generally good sources of 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.

Aug. 01, 2017 See more In-depth