Fuel foods: all carbohydrates are not created equal

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.

COPYRIGHT 1997 Aerobics and Fitness Association of America
COPYRIGHT 2004 Gale Group