Glycemic index: overview of implications in health and disease1–4
David JA Jenkins, Cyril WC Kendall, Livia SA Augustin, Silvia Franceschi, Maryam Hamidi, Augustine Marchie,
Alexandra L Jenkins, and Mette Axelsen
The concept of a glycemic index was developed to provide a numeric classification of carbohydrate foods on the assumption that such data would be useful in situations inwhich glucose tolerance is impaired. In many ways, the glycemic index concept was an extension of the dietary fiber hypothesis of Burkitt and Trowell (1), who suggested that foods that are more slowly absorbed may have metabolic benefits in relation to diabetes and to the reduction of coronary heart disease (CHD) risk. At the same time the dietary fiber hypothesis was formed, the concept of acluster of diseases related to central adiposity and intraabdominal fat mass with attendant insulin resistance was being developed (2–5). The similarity of many of the issues that were raised after the formulation of both concepts further defined possible preventive and therapeutic roles for the glycemic index classification of foods. The necessary research in this area was greatly facilitated by thecompilation of comprehensive glycemic index food tables (6).
GLYCEMIC INDEX AND GLYCEMIC LOAD
The glycemic index is the indexing of the glycemic response of a fixed amount of available carbohydrate from a test food to the same amount of available carbohydrate from a standard food consumed by the same subject (initially, the standard “food” was glucose, but more recently it has been whitebread; 7, 8). The blood glucose area after consumption of the test food was expressed as a percentage of the standard. The glycemic load, which assesses the total glycemic effect of the diet and has proved very useful in epidemiologic studies, is the product of the dietary glycemic index and total dietary carbohydrate (9–11). In general, the insulin responses, when measured, related well to glycemicresponses (12, 13). It also appeared that the rate of digestion of the food was an important determinant of glycemic response (14, 15). Thus, the rate of liberation of the carbohydrate products of digestion in vitro over 3–5 h reflected the blood glucose area in vivo (14). Intrinsic and extrinsic factors that alter the rate of gastrointestinal motility, digestion and absorption, and the nature ofthe starch, cooking method, particle size, and the presence of fiber, fat, and proteins were all found to result in differences in the glycemic index (16, 17).
The starchy staples of traditional cultures were often foods that had lower glycemic indexes, such as pasta, whole-grain pumpernickel breads, cracked wheat or barley, rice, dried peas, beans, and lentils (18, 19). It appears that thetraditional use of low-glycemicindex carbohydrate foods in the diet was particularly prevalent among cultures that are now experiencing high rates of diabetes, eg, the Pima Indians and the Australian Aborigines, and where the change to high-glycemic-index foods has been a more recent phenomenon (20–22). Obviously, many other factors, such as obesity and reduced physical activity, must play major rolesin increasing diabetes risk. Nevertheless, over time the desire for sweet foods, which resulted from rapid carbohydrate breakdown of starch in the mouth, may have resulted in the selection of rapidly digested (and hence high-glycemic-index foods) as cultures became more affluent (18).
Thus, foods with high glycemic indexes are proposed further as a dietary factor that favors the development ofchronic disease.
CONCERN OVER UTILITY OF THE GLYCEMIC INDEX
It is said that the glycemic index concept lacks clinical utility because differences in glycemic indexes between foods are lost once these foods are consumed in a mixed meal (23). Part of the reason for this is that when a mixed meal consists of several carbohydrate sources, the effect of the lower glycemic index...
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