Role of glycemic index and glycemic load in the healthy state, in prediabetes, and in diabetes

The choice of carbohydrate-rich foods in the habitual diet should take into account not only their chemical composition but also their ability to influence postprandial glycemia (glycemic index). Fiber-rich foods generally have a low glycemic index (GI), although not all foods with a low GI necessarily have high fiber content. Several beneficial effects of low-GI, high-fiber diets have been shown, including lower postprandial glucose and insulin responses, an improved lipid profile, and, possibly, reduced insulin resistance. In nondiabetic persons, suggestive evidence is available from epidemiologic studies that a diet based on carbohydrate-rich foods with a low-GI, high-fiber content may protect against diabetes or cardiovascular disease. However, no intervention studies have so far evaluated the potential of low-GI, high-fiber diets to reduce the risk of diabetes, although in studies aimed at diabetes prevention by lifestyle modifications, an increase in fiber consumption was often part of the intervention. In relation to prevention of cardiovascular disease, intervention studies evaluating the effect of a low-GI diet on clinical events are not available; moreover, the results of the few available intervention studies evaluating the effects of GI on the cardiovascular disease risk factor profile are not always concordant. The best evidence of the clinical usefulness of GI is available in diabetic patients in whom low-GI foods have consistently shown beneficial effects on blood glucose control in both the short-term and the long-term. In these patients, low-GI foods are suitable as carbohydrate-rich choices, provided other attributes of the foods are appropriate.