The glycemic index measures how fast a food is likely to raise your blood sugar. This can be helpful. For example, if your blood sugar is low and continuing to drop during exercise, you would prefer to eat a carb that will raise your blood sugar quickly. On the other hand, if you would like to keep your blood sugar from dropping during a few hours of mild activity, you may prefer to eat a carb that has a lower glycemic index and longer action time. If your blood sugar tends to spike after breakfast, you may want to select a cereal that has a lower glycemic index.

Learn more about the Glycemic Index and see a sample chart here.