Despite extensive study, the practical significance of the glycemic index of food is still debatable. The purpose of this review paper was to evaluate the effect of glycemic index on food intake and body weight based on the analysis of published studies about this topic. According to some authors, ingestion of high glycemic index diets tends to enhance appetite and promote positive energy balance. The increase of appetite associated with the ingestion of these diets is attributed to an especially sharp early post-prandial rise of blood glucose followed by a marked release of insulin and subsequent rebound relative hypoglycemia and low levels of blood fatty acids, suggesting the difficulty that the body has to access its stored metabolic fuels. Short-term investigations have generally demonstrated that ingestion of low glycemic index foods results in greater satiety and lower energy intake than high glycemic index foods. However, less is known about the importance of glycemic index to energy balance and weight control associated with chronic ingestion of foods differing in glycemic index. Carefully designed long-term studies are required to assess the efficacy of glycemic index in the treatment and prevention of obesity in humans.