Use of glycemic index in predicting risk of coronary heart disease

Department of Nutrition University of California One Shields Avenue Davis, CA 95616

Dear Sir:

I am writing regarding the article by Liu et al (1) in the June issue of the Journal. In the results section, the authors made the statement that "Women with high dietary glycemic loads consumed more carbohydrates, dietary fiber, cereal fiber, vitamin E, and folate...." This group apparently had lower intakes of fats and cholesterol and also smoked less than did women with low dietary glycemic loads. The authors did not appear to offer an explanation as to why these factors, which have been associated with a lower risk of coronary heart disease (CHD), occurred in the group that had the highest risk of CHD in their study. Are we to conclude that these other factors are unimportant relative to glycemic index in predicting the risk of CHD?

Liu et al used glycemic index to calculate what is referred to as glycemic load from food-frequency data. It is not clear what method was used to validate this approach, especially given that food-frequency data do not provide information on meal patterns, cooking methods, varieties of starchy foods, or other factors that may influence the actual glycemic index of carbohydrate-containing foods and meals, as consumed.

The authors observed that high glycemic load is most predictive of CHD risk in women with body mass indexes (in kg/m²) >23. This observation suggests that metabolic factors associated with weight gain may be more important in explaining the role of carbohydrate intake and the risk of CHD than are the glycemic indexes of foods per se. Is glycemic index a tool for understanding of these metabolic factors, or is it an end in itself?

REFERENCE

1. Liu S, Willett WC, Stampfer MJ, et al. A prospective study of dietary glycemic load, carbohydrate intake, and risk of coronary heart disease in US women. Am J Clin Nutr 2000;71:1455–61.