Dear Dr. Ettinger,
What is the Glycemic Index?
A: The Glycemic Index (GI) is a measuring system that ranks carbohydrates on the extent to which they raise blood sugars levels after eating. It makes a gram for gram comparison of carbohydrates in individual foods, and provides a measurable, evidence-based index of the concentration of glucose (sugar) in the blood. Dr. David J. Jenkins and colleagues at the University of Toronto originated the process in 1981.
After measurement, foods that score high on the Glycemic Index are rapidly digested and absorbed into the bloodstream, causing a glucose response marked by clear fluctuations in blood sugar levels to occur very quickly. Food with slower rates of digestion score lower on the Glycemic Index scale, indicate a more stable and longer-term energy source that causes gradual rises in blood sugar and insulin levels and a reduction of fats circulating in the blood. Foods with lower Glycemic Index scores can improve glucose and lipid levels in diabetics, control the appetite, delay hunger, and control the hormonal levels of insulin.
A low-scoring GI food product releases energy slowly, making them good food sources for diabetics, dieters, and endurance athletes, while high GI scores indicate substances that will raise blood sugar levels quickly and are best for recovering from endurance exercise routines. The glycemic effect of foods depends on the type of starch, the structure of the starch molecules themselves, fiber and fat content, and acidity levels. Glycemic levels can vary greatly depending on food variations, temperatures, ripeness, preparation, and processing. Also, the GI score of a meal with mixed items is hard to predict.
The Glycemic Index is primarily used for disease prevention and weight control. Evidence shows that people who stick to a low GI diet over the course of many years likewise reduce their risk of Type 2 diabetes and coronary heart disease. It is thought that the glycemic spikes from eating high GI foods may cause damage to the vascular system by free radicals, as well as by increased insulin levels. Recent studies show that hyperglycemia can cause an increased risk of atherosclerosis and coronary heart disease in patients without diabetes. It is further believed that increased consumption of high GI carbohydrates increases the risk of obesity.
