The Skinny on the Glycemic Index
Although developed to help people with diabetes manage their food intake, the glycemic index has taken on new meaning as a weight loss strategy. In fact, several diet books tout the glycemic index as a foolproof way of identifying foods that raise blood sugar and insulin levels and therefore, can lead to weight gain.
But despite the hype, experts in nutrition and public health see very little practical use for the glycemic index and even the American Diabetes Association does not recommend this system for the prevention or treatment of diabetes. This is because of the many factors that affect the digestion of carbohydrates in the body. In fact, there is no clear evidence that avoiding foods high on the index is even beneficial.
The following describes what the glycemic index is and why the public health community does not recommend it in designing an eating plan.
The Glycemic Index and Its Limitations
Originally developed in 1981 as a laboratory tool to measure the rate at which carbohydrates are metabolized, the glycemic index is now being used by some as a measure of the degree to which a specific food raises a person's blood sugar, which in turn affects insulin levels in the body. GI is calculated by measuring the effect of 50 grams of carbohydrates from various foods against a "standard" response from 50 grams of glucose. The higher the number, the greater the food's effect on blood sugar.
The reason for all the interest in the index is because it supports the theory of "net carbs," which has facilitated the creation of the low-carb food industry and the launch of thousands of "low-carb" products. The theory is that high-GI foods cause a spike in the glucose level that prompts the body to release a flood of insulin. In turn, insulin drops blood sugar levels so that the person feels hungry again quickly and eats more. In contrast, low-GI foods are said to be digested more slowly and to release glucose more gradually.
But while many popular diet books make it sound as if the glycemic index is an accepted theory, in truth, there are very real problems with this system. First and foremost is the fact that the glycemic index deals with single foods eaten alone, not meals where foods are combined.
At the same time, this system does not take into account the serving size of commonly eaten foods or the fact that there can be major differences even when comparing foods of the same type, such as a relatively green banana compared with a ripe one. Another major limitation of the glycemic index is that it doesn't take into account the many factors that can alter the digestion and absorption of carbohydrates. These factors include the amount of fiber, fat and protein in the food, how refined the ingredients are, whether the food was cooked, and what other foods are eaten at the same time.
Along with these limitations, there is no clear-cut evidence in the scientific literature that associates low-GI foods as either promoting satiety or reducing hunger. Moreover, nutritionists state that eliminating all foods that are high on the glycemic index is unhealthy, since many of these carbohydrates are rich in vitamins and minerals, phytochemicals, antioxidants and dietary fiber that have been associated with a lower risk for certain cancers, diabetes, cardiovascular disease and stroke, among other medical conditions. What is even more troubling is that many foods that have a low GI score, such as chocolate bars, are known to be high in fat and calories, while foods such as carrots with a high GI score are not.
The Implications for People with Diabetes
Because the glycemic index was developed to measure how fast blood sugar rises after a person eats foods containing carbohydrates, it is important to note that the premier organization focusing on the prevention and treatment of diabetes -- the American Diabetes Association -- does not recommend the use of this system. In its January 2002 nutrition recommendations, ADA stated that the available studies where glycemic index was controlled "do not provide convincing evidence of a benefit."1 In addition, ADA's statement said that the research examining the index is very limited and involves only a small number of study groups. Therefore, ADA concluded, "the data reveal no clear trend in outcome benefits."
Rather, the ADA along with all the leading nutrition and public health groups recommend that for optimal health as well as weight loss, people should consume a diet that includes a variety of carbohydrate-containing foods, and especially fruits, vegetables, whole grains and low-fat dairy products. Moreover, nutrition authorities are unanimous in stating that for weight loss, calories count, not the glycemic index. Although it may sound old-fashioned, the simple fact is that the key to successful weight loss is a combination of a reduced-calorie diet and increased physical activity -- nothing more.
