Glycemic Index

The level of glycogen in the muscles before starting exercise is the most important fuel determinant of performance. Eating a specific food at a specific time in relation to exercise can affect when glucose is released into the blood. Glucose, a monosaccharide, is commonly called “blood sugar”. All cells of the body metabolize glucose for energy. It is the most important monosaccharide in the human body. The Glycemic Index (GI) is determined primarily by the rate of absorption of a food into the body. See list of high carbohydrate foods with glycemic index. Knowing the Glycemic Index of foods is important for athletes needing to replenish their muscle's glycogen levels following difficult and demanding workouts and activities.

Glycemic Load (GL) is the total amount of carbohydrate contained in each food, food preparation or meal. Individuals that need to monitor their carbohydrate intake need to be cognizant of glycemic load as well as the glycemic index to aid in controlling blood glucose levels after meals. Diabetics need to be particularly sensitive to this issue. Both glycemic load and the glycemic index are needed to predict blood glucose levels following meals. Serving sizes and the type of carbohydrate therefore, have a significant impact on blood glucose levels and insulin demand.

*Glycemic Load = (GI value x carbohydrate per serving)/100

Ex: 1 orange: 48 x 11g = 528/100 = 5.28 = 5 (Glycemic Load value)

Ex: 250 ml (approx. 1 cup) Gatorade: 78 x 15g = 1170/100 = 11.7 = 12 (Glycemic Load value)

An average diet of 2000 calories per day striving to achieve 60% of calories from carbohydrates needs a 300 GL value of carbohydrates in the foods one eats. Ex: (300 (grams of carbohydrates) x 4 (carb kcal/gram) x 100 (pure glucose GI value)/2000 = 60 %.

Some factors that affect the rate of digestion of a food include: fiber content, sugar type, amount of protein or fat in the food, degree of processing of the food, type of starch and the way the food is prepared. *The most important factor is the physical state of the starch in the food which is manipulated during food processing by grinding it into fine particles or heating it to expand and burst both of which make digestion easier and faster thereby raising blood glucose levels more quickly.

Complex carbohydrates are low to moderate glycemic foods, simple sugars and processed foods are high glycemic foods. The best sources of establishing and maintaining high levels of glycogen for storage are the complex carbohydrates.

Moderate to high glycemic index foods are the best sources of energy replacement following strenuous exercise. It may take up to 20 hours for the body to replenish muscle glycogen stores. The most important factors for resynthesis are the rate and timing of carbohydrate ingestion and type of carbohydrate, hence the understanding necessary by the individual regarding the importance of the glycemic index.

 

HIGH GLYCEMIC FOODS:

Some common examples are: Sugars, syrups, honey, molasses, Gatorlode, Gatorade, soft drinks, muffins, pancakes, waffles, white bread, whole meal bread, kaiser roll, shredded wheat, bread sticks, bagels, graham crackers, baked potatoes, Grapenuts cereal, Mini Wheats whole wheat breakfast cereal, Rice Krispies cereal, corn flakes cereal, raisin bran cereal, Bran flakes cereal, Total cereal, Cheerios cereal, cupcakes, doughnuts, croissants, white and brown rice, new potatoes, chocolate PowerBar, raw pineapple, double chocolate Pop Tarts, boxed macaroni and cheese, plain or cheese pizza, plain micro-waved cooked popcorn, sweet corn, carrots, beets, raisins, dates, cranberry juice cocktail, watermelon, tomato sauce, parsnips, puffed rice cakes, pretzels, regular ice cream, and winter squash.

MODERATE GLYCEMIC FOODS:

Some examples are: Spaghetti, macaroni, white pasta, whole grain rye bread, stuffing, oatmeal, sweet potatoes, All-bran cereal, potato chips, sucrose, whole wheat pasta, grapes, fresh apricots, peas, oranges, orange juice, fresh and canned peaches in heavy syrup or natural juice, grapes, baked beans, corn, unsweetened grapefruit juice, mango, low fat ice cream, custard, instant pudding and yams.

LOW GLYCEMIC FOODS:

Butter beans, chick peas, green beans, green peas, kidney beans, navy beans, red lentils, skim milk, whole milk, fruit yogurt, ice milk, baked beans, apples, fish sticks, lentils, sausage, fructose, peanuts, fresh grapefruit, fresh cherries, dried apricots, premium ice cream, and low fat yogurt.

References

Alters S. and Schiff W. Essential Concepts for Healthy Living. (3rd Ed.) Boston. 2003.

Bonci L. Nutrition Conditioning Goals for Athletes. University of Pittsburgh Medical Center Health System. 2004.

*Brand-Miller J, Wolever MS, Foster-Powell K, & Colagiuri S. The New Glucose Revolution. Marlowe & Co., New York. 2005.

Coyle E, and Coyle E. Carbohydrates that speed recovery. Phys Sports Med 1993; 21:2. pp. 111-123.

Exercise, ETC, Inc. Insulin, Protein and Fat. 2002.

McArdle W, Katch F, & Katch V. Sports and Exercise Nutrition. (2nd Ed.) Lippincott Williams & Wilkins. Boston. 2005.

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Last updated 3/31/2006 by MIT Sports Medicine: K Davis

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