The Glycemic Index is a way of classifying foods. Each food is rated according to the reaction it causes on blood glucose levels, and is given a ranking out of 100. Glucose has a score of 100. High GI foods cause fast, and large increases in blood glucose levels, resulting in large releases of insulin to store the glucose. A diet of high GI foods can cause the body to become insulin resistant. This means the insulin is much less effective at controlling blood glucose levels, and a continued high GI diet is likely to result in type 2 diabetes or heart disease.
Health professionals therefore recommend a diet consisting of low GI foods.