Glycemic index, or GI, measures how quickly digested foods change the body's blood sugar level, and a ranking of 55 or under is considered low, according to the Mayo Clinic. Foods with a low GI are absorbed at the slowest rate, raising blood sugar at a healthy, controlled pace. A medium GI ranges from 56 to 69, and high GI ranges from 70 to 100.
Carbohydrates are broken down into simple sugar units, known as glucose, and converted into blood sugar to provide cells with energy, the Mayo Clinic states. The body produces the hormones insulin and glucagon to balance an insufficient or excess supply of blood sugar. Overconsuming high-GI foods can stimulate sharp increases or unstable fluctuations in blood sugar, leading to conditions such as diabetes, heart disease and high blood pressure.
Processed foods often rank high on the GI scale, while most whole grains, nonstarchy vegetables, dried beans and fruits and other high-fiber foods have a medium or low GI, according to the American Diabetes Association. Low-GI foods are valuable for weight control because they help slow digestion and satisfy appetite, but diners should also pay equal attention to cooking methods, processing, nutritional content, ripeness and portion size when planning meals.