The glycemic index can be a helpful tool in managing your blood sugar, but it can also serve as a guide when planning meals and snacks that will fuel your workouts. Carbohydrate-containing foods that stabilize your blood sugar can provide sustained energy during exercise and help you recover more efficiently. By exercising regularly and eating foods that keep your blood sugar within a healthy range, you may also lower your risk of type 2 diabetes.
Glycemic Index
The glycemic index, or GI, measures the effects of foods on your blood sugar. Based on a scale of 1 to 100, the GI determines how quickly and how significantly a food will increase your blood glucose level. The GI only measures foods that contain carbs. Foods with a low GI value raise your blood sugar slowly, providing a gradual release of energy as your body converts the food's carb content into glucose.
Planning
To make the most of your workouts, focus on foods with a low GI value, advises the Glycemic Index Foundation. Eating a meal with a low GI value before your workout helps you maintain a stable blood glucose level during exercise and may increase the amount of fat that you burn. Eating a pre-workout meal with a high GI value can cause your blood sugar to peak before you start your exercise and plunge before you've completed your workout. MayoClinic.com recommends eating a light meal two to three hours before exercise to prevent low blood sugar and allow your food to digest. Within two hours after your workout, eat a light meal of complex carbs and protein to replenish glycogen, a stored form of energy that your body uses during exercise, advises MayoClinic.com.
Benefits
Eating a low-GI meal about an hour before your workout may improve your endurance, according to a study published in the "American Journal of Clinical Nutrition." A group of athletes who ate a low-GI meal of lentils one hour before an event were able to exercise longer than a group who ate a high-GI meal of potatoes. However, the benefits of low-GI foods and exercise aren't limited to endurance athletes. Recent research indicates that a low-GI diet, in combination with regular physical activity, can prevent insulin resistance in overweight adults who are at risk for developing Type 2 diabetes.
Examples
A light pre-workout meal containing whole wheat pasta, dried beans or whole-grain cereal can provide energy without raising your blood sugar. All of these complex carbs are low-GI foods, meaning they have a GI value less than 55. Adding a lean protein, such as chicken or fish, or a nonstarchy vegetable such as spinach or lettuce, will not add to the GI value of your meal because these foods have such a minimal effect on blood glucose levels that their GI value can't be measured.
Considerations
Although all low-GI complex carbs provide sustained energy, you may want to avoid certain carb-rich foods before an endurance event, says MayoClinic.com. Bran cereal, beans or fruit may cause gas or diarrhea during an intense workout. MayoClinic.com advises avoiding foods that are high in fat---even healthy, unsaturated fat---before workouts, as dietary fat can linger in your stomach and cause discomfort during exercise.
References
- MayoClinic.com: Eating and Exercise--Time It Right to Maximize Your Workout
- GlycemicIndex.com
- PubMed: Low-Glycemic Index Diet Combined with Exercise Reduces Insulin Resistance, Postprandial Hyperinsulinemia and Glucose-Dependent Insulinotropic Polypeptide Responses in Obese, Prediabetic Humans
- "American Journal of Clinical Nutrition"; "Carbohydrate Feeding Before Exercise and the Glycemic Index"; Diana Thomas et al; 1994
