Food glycemic index, as given in glycemic index tables, is a significant determinant of glycemic responses elicited by composite breakfast meals.

BACKGROUND: Recent studies have concluded that the carbohydrate content and glycemic index (GI) of individual foods do not predict the glycemic and insulinemic effects of mixed meals. We hypothesized that these conclusions may be unwarranted because of methodologic considerations. OBJECTIVE: The aim was to ascertain whether the GI and carbohydrate content of individual foods influence glucose and insulin responses elicited by realistic mixed meals in normal subjects. DESIGN: With the use of a crossover design, we determined the glucose and insulin responses of 6 test meals in 16 subjects in Sydney and the glucose responses of 8 test meals in 10 subjects in Toronto and then the results were pooled. The 14 different test meals varied in energy (220-450 kcal), protein (0-18 g), fat (0-18 g), and available carbohydrate (16-79 g) content and in GI (35-100; values were rounded). RESULTS: The glucose and insulin responses of the Sydney test meals varied over a 3-fold range (P < 0.001), and the glucose responses of the Toronto test meals varied over a 2.4-fold range (P < 0.001). The glucose responses were not related to the fat or protein content of the test meal. Carbohydrate content (P = 0.002) and GI (P = 0.022) alone were related to glucose responses; together they accounted for 88% of the variation in the glycemic response (P < 0.0001). The insulin response was significantly related to the glucose response (r = 0.94, P = 0.005). CONCLUSIONS: When properly applied in realistic settings, GI is a significant determinant of the glycemic effect of mixed meals in normal subjects. For mixed meals within the broad range of nutrient composition that we tested, carbohydrate content and GI together explained approximately 90% of the variation in the mean glycemic response, with protein and fat having negligible effects.

Glycemic load and chronic disease.

The glycemic index (GI) has proven to be a useful nutritional concept, providing new insights into the relationship between foods and chronic disease. Observational studies suggest that diets with a high glycemic load (GI x carbohydrate content) are independently associated with increased risk of type 2 diabetes and cardiovascular disease. Postprandial hyperglycemia plays a direct pathogenic role in the disease process. Lower glucose and insulin levels are associated with improved risk profile, including high-density lipoprotein cholesterol, glycosylated proteins, oxidative status, hemostatic variables, and endothelial function. Limited evidence suggests that a low-GI diet may also protect against obesity, colon cancer, and breast cancer. Diets with a high glycemic load may affect health differently in insulin-resistant and insulin-sensitive individuals. Improvements in postprandial hyperglycemia can be brought about by manipulating either the type (i.e., GI) or amount of dietary carbohydrate, or both; at present, the GI appears to be more effective.

International table of glycemic index and glycemic load values: 2002.

Reliable tables of glycemic index (GI) compiled from the scientific literature are instrumental in improving the quality of research examining the relation between GI, glycemic load, and health. The GI has proven to be a more useful nutritional concept than is the chemical classification of carbohydrate (as simple or complex, as sugars or starches, or as available or unavailable), permitting new insights into the relation between the physiologic effects of carbohydrate-rich foods and health. Several prospective observational studies have shown that the chronic consumption of a diet with a high glycemic load (GI x dietary carbohydrate content) is independently associated with an increased risk of developing type 2 diabetes, cardiovascular disease, and certain cancers. This revised table contains almost 3 times the number of foods listed in the original table (first published in this Journal in 1995) and contains nearly 1300 data entries derived from published and unpublished verified sources, representing > 750 different types of foods tested with the use of standard methods. The revised table also lists the glycemic load associated with the consumption of specified serving sizes of different foods.

Glycemic index and obesity.

Although weight loss can be achieved by any means of energy restriction, current dietary guidelines have not prevented weight regain or population-level increases in obesity and overweight. Many high-carbohydrate, low-fat diets may be counterproductive to weight control because they markedly increase postprandial hyperglycemia and hyperinsulinemia. Many high-carbohydrate foods common to Western diets produce a high glycemic response [high-glycemic-index (GI) foods], promoting postprandial carbohydrate oxidation at the expense of fat oxidation, thus altering fuel partitioning in a way that may be conducive to body fat gain. In contrast, diets based on low-fat foods that produce a low glycemic response (low-GI foods) may enhance weight control because they promote satiety, minimize postprandial insulin secretion, and maintain insulin sensitivity. This hypothesis is supported by several intervention studies in humans in which energy-restricted diets based on low-GI foods produced greater weight loss than did equivalent diets based on high-GI foods. Long-term studies in animal models have also shown that diets based on high-GI starches promote weight gain, visceral adiposity, and higher concentrations of lipogenic enzymes than do isoenergetic, macronutrientcontrolled, low-GI-starch diets. In a study of healthy pregnant women, a high-GI diet was associated with greater weight at term than was a nutrient-balanced, low-GI diet. In a study of diet and complications of type 1 diabetes, the GI of the overall diet was an independent predictor of waist circumference in men. These findings provide the scientific rationale to justify randomized, controlled, multicenter intervention studies comparing the effects of conventional and low-GI diets on weight control.