Blood Glucose Response Curves
The glycemic index or glycaemic index is a measure of how the body reacts to dietary carbohydrates. Carbohydrates that increase blood glucose quickly have a high glycemic index and they are called high GI foods. Carbohydrates that break down slowly and produce a gradual rise in blood glucose are considered low GI foods.
The glycemic index was developed by Dr. D.J. Jenkins and his associates at the University of Toronto in an effort to find better diets for patients with diabetes.[1,2] The glycemic index of a food is calculated based on the area under the two hour blood glucose response curve after the ingestion of a specific weight of carbohydrate (usually 50 grams). To obtain the GI, the area under the curve of the test food is divided by the area of the standard (glucose) and multiplied by 100. An average GI value for a food may be calculated from data collected from several human subjects.
Diabetes is a metabolic disease that elevates the level of blood sugar, either because the body does not produce enough insulin, or because the cells of the body do not respond to the insulin that is produced. Low GI foods help diabetics maintain better control of their blood sugar levels by reducing the rate at which sugars are absorbed by the body.
The difference between high GI and low GI carbohydrates is due to their chemical structure. Glucose, which is a simple sugar (high GI), is absorbed very rapidly and causes large increases in the blood sugar level. Complex carbohydrates (low GI), on the other hand, need to be hydrolyzed before they can be converted into simpler carbohydrates that can be assimilated by the body. Some of the complex carbohydrates are metabolized by the intestinal microflora into short chain fatty acids which do not elicit a glycemic response at all. Thus, even with the same amount of total carbohydrate, a low GI meal produces fewer sugars that can increase the blood glucose level.
 Jenkins DJ, Wolever TM, Taylor RH, et al. Glycemic index of foods: a physiological basis for carbohydrate exchange. Am J Clin Nutr 1981;34:362–6.
 Foster-Powell K, Holt SH, Brand-Miller JC. International table of glycemic index and glycemic load values: 2002. Am J Clin Nutr 2002;76:5–56.