Is glycemic index of food a feasible predictor of appetite, hunger, and satiety?

This review assesses the feasibility of using glycemic index (GI) as a predictor of appetite, hunger and satiety by surveying published human intervention studies. We also discuss the relationship between GI and two appetite/satiety control hormones, leptin and ghrelin. Ingestion of high-GI food increased hunger and lowered satiety in short-term human intervention studies. This effect may be attributed to the rapid decline in blood glucose level following a hyperinsulinemic response caused by a sharp and transient increase in blood glucose level that occurs after the ingestion of high-GI food, which is defined as the glucostatic theory. However, appetite, hunger and satiety after the ingestion of foods with varying GI were inconsistent among long-term human intervention studies. From the few relevant long-term studies available, we selected two recent well-designed examples for analysis, but they failed to elicit clear differences in glycemic and insulinemic responses between high- and low-GI meals (consisting of a combination of different foods or key carbohydrate-rich foods incorporated into habitual diets). One of the reasons that these studies could not predict glycemic response to mixed meals is presumably that the GI of each particular food was not reflected in that of the mixed meals as a whole. Thus, it is difficult to conclude that the GI values of foods or mixed meals are a valid long-term predictor for appetite, hunger and satiety. Both insulin and insulin-mediated glucose uptake and metabolism in adipose tissue affect blood leptin concentration and its diurnal pattern. Circulating ghrelin level is suppressed by carbohydrate-rich meals, presumably via glycemia and insulinemia. Accordingly, low-GI foods may not necessarily increase satiety or suppress appetite and/or hunger because of the lack of insulin-mediated leptin stimulation and ghrelin suppression. However, insulin-mediated leptin stimulation and ghrelin suppression per se is not consistent among studies; thus we were not able to identify a clear relationship among GI, satietogenic leptin, and appetitic ghrelin.