The plan consists of three phases. In the first, carbs are curtailed dramatically in order to stop cravings. Next, dieters keep blood sugar on an even keel by adding back small amounts of slow-to-digest “good” carbs like whole grains, fruits, and vegetables. Without getting too complicated, foods are categorized based on a ranking system called the glycemic index (G.I.), which measures their ability to raise blood sugar. Foods with low G.I.’s are favored because they are digested and absorbed slowly and release sugar into the blood gradually; colas, sugar, and refined grains are downplayed since they have a high G.I. Simply put, “the faster the sugars and starches you eat are processed and absorbed intro your bloodstream, the fatter you get,” Agatston says.