In 2004, James W. Anderson, MD, Professor of Internal Medicine at the University of Kentucky Graduate Center for Nutritional Sciences, and his colleagues reviewed nine randomized control trials (considered the strongest experimental research) on low-glycemic-index diets. They found that the consensus among the nine trials is that low-glycemic-index diets are associated with lower blood glucose levels, lower LDL (“bad”) cholesterol levels, lower triglycerides, and higher HDL (“good”) cholesterol levels. As a result, they recommended that information about the glycemic index be included in diabetes education and in the Exchange Lists for Meal Planning.
Currently the diabetes associations of Australia, Britain, Canada, Germany, Japan, and South Africa endorse the use of the glycemic index in meal planning. Diabetes Australia recommends eating at least three foods with a low glycemic index daily, preferably one at each meal. The World Health Organization also backs the use of the glycemic index in diabetes management. The American Diabetes Association clinical recommendations for diabetes care acknowledge the potential benefits of following a low-glycemic diet, particularly for people who currently have a high-glycemic diet.
Chronic disease and weight control
Use of glycemic index values and the concept of glycemic load may have benefits that go beyond blood glucose control. Some research — though not all — has found associations between high-glycemic-index and/or high-glycemic-load diets and cancer (breast, ovarian, endometrial, and colorectal), coronary heart disease and heart attacks, macular degeneration, high cholesterol and triglycerides, and high C-reactive protein (a marker of general inflammation in the body).
In 2006, The New England Journal of Medicine published a study that found a 30% reduction in risk of coronary heart disease among women on low-carbohydrate (and therefore low-glycemic-load) diets in which the sources of protein and fat were predominantly vegetarian. This study also found a strong positive association between high-glycemic-load diets and coronary heart disease. Since no data on lipids (cholesterol and triglycerides) were obtained, the study did not establish any association between a low-glycemic-load diet and blood lipid levels, but other research has found a beneficial effect on them.
Since many chronic diseases are linked with overweight and obesity, some researchers have examined whether low-glycemic-index, low-glycemic-load diets can affect appetite and encourage weight loss. While the previously mentioned study showed no association between low-carbohydrate diets and weight over the long term, two studies have shown that low-glycemic-index diets may be especially effective in helping women reduce waist circumference, body fat, and body weight. (In the study reported in The New England Journal of Medicine, the subjects were not following the low-carbohydrate diet to lose weight, and that may have affected results.) The direct effect of the glycemic index on body weight and body fat is still widely debated.
Yet another study using a group of both men and women showed an increased risk of Type 2 diabetes in subjects who consumed high-glycemic-index diets and did not have abdominal obesity, particularly those whose waist size increased during the study. However, the researchers did not find the same increase in risk based on dietary glycemic load or carbohydrate intake.
Appetite control is one of the main tenets of popular diet programs that advocate low-glycemic-index, low-glycemic-load diets for weight loss, but scientific research on appetite control has had conflicting results. For example, a study published in the September 2005 issue of the journal Diabetes Care in which some subjects consumed only high-glycemic-index foods and some consumed only low-glycemic-index foods reported no differences in perceived appetite or in food intake after eight days of these diets. However, this study has been criticized by other researchers who say that the glycemic index values of the foods used in the study were miscalculated, so the results are faulty.