When it comes to managing your weight, the two most important letters you need to know are G and I. They stand for glycemic index - and they've become the buzzwords of the diet movement in recent years. The Glycemic Index chart ranks carbohydrates based on their effect on blood sugar levels. Carbs that break down fast and lead to blood sugar spikes are given a high value while carbs that move through the body slow are assigned a low value. With the glycemic index, foods are given values based on how quickly the blood sugar levels rise. Foods are ranked on a scale from 0 to 100. Proponents of the glycemic index believe the more low G.I. foods you consume the better for your blood sugar. For example, a doughnut has a G.I. of 76. Yogurt, on the other hand, has a G.I. value of 14. High glycemic foods include white bread (71), corn chips (74), waffles (76), jelly beans (80), pretzels (81) and parsnips (97).