The Cooper Institute

Founded in 1970 by the "Father of Aerobics"
Kenneth H. Cooper MD, MPH


Glycemic Index: Hope or Hype for Weight Loss?

Posted in
Eat better

Thursday, Aug 20, 2015

The glycemic index (GI) for carbohydrate-containing foods and beverages was developed in the early 1980’s in order to try to improve blood glucose control in diabetic patients. The GI of a food or beverage is determined by the rise in blood glucose levels during the two-hour period following its ingestion versus the blood glucose response to an equivalent amount of carbohydrate in a standard food such as white bread.1  As a reference point, white bread has a GI of 100. Foods and beverages with a higher GI than 100 (e.g. instant rice) cause a higher rise in blood glucose than white bread, while foods and beverages with a lower GI than 100 cause less of a rise in blood glucose than white bread. For example, if a food had a GI of 33, it would cause only about one-third of the increase in blood glucose as compared to eating an equivalent amount of white bread. Examples of high and low GI foods are shown in Table 1 below.

Table 1. Examples of high GI and low GI foods.

High GI foods Low GI foods
White bread Beans
Instant rice Apples
Baked potato Whole grains
Corn flakes Apple
Raisins Chocolate
Carrots Milk
Watermelon Bran cereal
Non-diet soft drinks French fries
Pretzels Full-fat ice cream
Some popular diets, e.g. South Beach, Atkins, and The Zone recommend the use of the GI to determine what foods should be consumed in order to lose weight and maximize health. There are many limitations and flaws to this type of approach:

The GI of any individual food is based on consuming an amount of that food which contains 50 grams of carbohydrate. For example, the GI of carrots is based on consuming 3.5 cups of carrots at one time. That’s a lot of carrots!

The GI is based on consuming a food by itself on an empty stomach. Very few of us would eat a just plain baked potato (or just 3.5 cups of carrots) on an empty stomach. Most of the time we consume carbohydrate-containing foods in combination with other foods that contain fat and/or protein. The GI goes ‘out the window’ when this occurs.

Individuals have different blood glucose and insulin responses to the same food. More specifically, fit individuals have a smaller rise in blood glucose and insulin levels than unfit individuals when given the same amount of carbohydrate-containing food.

Weight that is lost on a low GI type of diet plan occurs simply because so many foods are restricted, or even eliminated. When foods are restricted, people tend to consume significantly fewer calories than they did previously. Therefore, the weight loss occurs because of negative caloric balance, not because people are consuming low GI foods.

The ripeness of a food can affect its GI.  For example, the GI of bananas can range from 30 (greenish colored-banana) to 70 (yellow and brownish-colored banana).

Perhaps the greatest limitation of using the GI to determine whether or how often a carbohydrate-containing food should be consumed is that it does not consider the nutrient or fiber content of the food. For example, a bowl of full-fat ice cream would have a low GI but is loaded with saturated fat and calories. On the other end of the spectrum corn, carrots, and raisins have a high GI, but are a great source of fiber, vitamins, minerals, and phytochemicals (non-nutrients found in plant-based foods that have been shown to help prevent disease).

For athletes who are training daily, it is extremely important to replace muscle and liver glycogen stores that are depleted each day. Many studies have shown that consuming high GI foods and beverages during the 30-60 minute period post-exercise actually speeds up glycogen synthesis, thus speeding up recovery from exercise!

Since individuals with diabetes struggle to control their blood glucose level, it might be of interest for you to know what the American Diabetes Association (ADA) has to say about the GI. In their latest recommendations, the ADA states that individuals with diabetes do not have to limit their food choices to those that have a low GI. Instead, people with diabetes should focus on the nutrient and fiber content of carbohydrate-containing foods, as well as the amount of carbohydrate consumed. The amount of carbohydrate consumed is known as glycemic load.

It is interesting to note that none of the fad diets which promote use of the GI have been shown to be effective for long-term weight loss or improvements in health.

As was eloquently stated several years ago by Dr. Xavier Pi-Sunyer, a very well-known expert in diabetes, “People and the experts advising them on nutrition can find more worthwhile issues to concentrate on than the glycemic index.” That sums it up quite nicely I think!

To learn more about obesity, physical activity, healthy eating and risk of chronic disease, take our Nutrition for Health and Fitness (NHF) course. You need not be a health and fitness professional or an athlete to attend; everyone is welcome to these workshops!



  1. Foster-Powell, K., Miller, J.B. (1995). International tables of glycemic index.  Am J Clin Nutr. 62:871S-893S.