Athletes were once told to choose starchy complex carbohydrates such as bagels, potatoes and bread for pre-exercise snacks. These foods were thought to contribute to a stable blood sugar level while sugary simple carbohydrates, in contrast, were thought to trigger a 'sugar high.' Of course, a 'sugar low' followed with a debilitating hypoglycemic reaction.
Today, research indicates otherwise. We now know a carbohydrate's effect upon blood sugar cannot be determined by whether it is a simple or complex carbohydrate, but rather by its glycemic response -- that is, the food's ability to elevate blood sugar. Glycemic response is influenced by many factors, including the amount you eat, fiber content, fat content or amount of added fat, and the way the food is prepared. For example, pasta has a lower glycemic response than bread, although both are made from wheat. Also, sugar added to ice cream has a much lower glycemic response than sugar alone.
By knowing a food's glycemic response, you can determine when to eat a certain food. High glycemic carbohydrates (such as potatoes, rice and honey) quickly enter the bloodstream and are best eaten during or after exercise. They are readily available to be used for energy or to refuel muscles. Low glycemic carbohydrates (such as apples, lentil soup, yogurt and kidney beans) slowly enter the bloodstream and are advantageous before exercise because they provide sustained energy. Low glycemic carbs may enhance your ability to maintain normal blood sugar levels during prolonged exercise.
The glycemic response partially explains why an energy bar with added fat or fiber enhances endurance. Any low glycemic food would likely have the same effect. Nevertheless, the right carb choices can enhance endurance if you will be exercising for more than 60 minutes, and also recovery time after hard exercise when you are depleted of carbs.
How much does the glycemic response really affect performance? In one research study, cyclists who ate low glycemic lentils before they exercised to exhaustion were able to pedal hard for 117 minutes, in contrast to only 97 minutes when they ate high glycemic potatoes.
The following Glycemic Index (GI) ranks carbohydrates in terms of their effect on blood sugar based on 50 gram portions. The GI of most foods can be lowered by adding fat, such as cream cheese, peanut butter, margarine or cheese to bread, bagels, potatoes or other carbohydrate-rich foods.
High GI Glucose 100 Potato, baked 85 Corn flakes 84 Rice cakes 82 Potato, microwaved 82 Jelly beans 80 Vanilla wafers, Nabisco 77 Cheerios 74 Cream of Wheat, instant 74 Graham crackers 74 Honey 73 Watermelon 72 Bagel, Lender's white 72 Bread, white 70 Bread, whole wheat 65-75 Shredded wheat 69 Soft drink, Fanta 68 Mars Bar 68 Grapenuts 67 Stoned wheat thins 67 Cream of Wheat, regular 66 Couscous 65 Table sugar (sucrose) 65 Raisins 64 Oatmeal 42-75 Ice cream 36-80 Muffin, bran 60 Moderate GI Bran Chex 58 Orange juice 57 Rice, white long grain 56 Potato, boiled 56 Popcorn 55 Rice, brown 55 Corn 55 Sweet potato 54 Pound cake, Sara Lee 54 Banana, overripe 52 Peas, green 48 Bulgur 48 Baked beans 48 Rice, white parboiled 47 Lentil soup 44 Orange 43 All-bran cereal 42 Spaghetti (no sauce) 41 Pumpernickel bread 41 Apple juice, unsweetened 41 Low GI Apple 36 Pear 36 Chocolate milk 34 Fruit yogurt, low-fat 33 Chick peas 33 Lima beans, frozen 32 Milk, skim 32 Apricots, dried 31 Green beans 30 Banana, underripe 30 Lentils 29 Kidney beans 27 Milk, whole 27 Barley 25 Grapefruit 25 Pure fructose 23
Nancy Clark, M.S., R.D., offers private nutrition consultations at Sports Medicine Brookline in the Boston area. Her popular Sports Nutrition Guidebook ($18) and NYC Marathon Cookbook and Nutrition Guide ($23) are available at your local bookstore or Sports Medicine Brookline, 830 Boylston St., Brookline, MA 02167; (617) 739-2003.
