 |
 |
|
||||||||||||
 |
||||||||||||||
 |
 |
|
 |
|||||||||||
|
||||||||||||||
Carbohydrates are the most efficient fuel for energy production. They can also be stored as glycogen in muscles and the liver, functioning as a readily available energy source for prolonged, strenuous exercise. For these reasons, carbohydrates may be the most important nutrient for sports performance. The diet has two stages: Depletion—The athlete performs the sport to the point of exhaustion to deplete stored carbos in specific muscles. Then the athlete follows a high-fat, low-carbohydrate diet for three days.Carbo-loading—A high-carbohydrate diet (400 to 600 grams of carbohydrate per day) is eaten for three days while training is reduced.Modified versions of this diet eliminate the depletion stage, or require a smaller amount of carbohydrate to be eaten, and appear to produce similarly effective results. Ready, set, go! Follow the advice of a trained exercise expert when using this diet. Emphasise whole grains, starchy vegetables, fruits, low-fat dairy products, and carbohydrate-replacement drinks. Reduce intake of fatty foods to achieve a relatively high-carbohydrate diet. Why do people follow this diet?A carbohydrate-loading diet (also known as carbo loading) is a strategy used by endurance athletes to increase muscle glycogen reserves in order to improve performance. Glycogen is the body’s storage form of glucose, the chief energy source for the body. When carbohydrates are consumed, the body changes much of them into glucose. Glucose that is not needed immediately is stored as glycogen in the muscles for later use. Normal levels of muscle glycogen are more than enough to maintain exercise lasting less than 75 minutes. However, intensive training in endurance sports lasting longer than an hour depletes muscle glycogen stores, increasing the need for carbohydrate intake to assure normal levels of blood glucose and sufficient muscle glycogen reserves. What do the advocates say?Research has found that carbohydrate-loading diets improve endurance athletes’ performance. Carbohydrate loading can be accomplished in two stages: the depletion stage and the carbohydrate-loading stage. On day one of the depletion stage, the athlete trains to exhaustion in his or her sport in order to deplete muscle glycogen in specific muscles. The athlete must engage in the sport during this stage because carbohydrate loading only occurs in the specific muscles exercised. For the next three days, a high-fat, low-carbohydrate diet (60 to 120 grams carbohydrate) is consumed while the athlete trains moderately. During the carbohydrate-loading stage, the diet is switched to a high-carbohydrate intake (400 to 600 grams carbohydrate) for the next three days, while training time is reduced. This will result in muscle glycogen “packing,” increasing the muscle glycogen to a new, higher level. Following a less stringent, modified carbohydrate-loading diet can eliminate potential problems with the classic carbohydrate-loading diet. The modified carbohydrate-loading plan is followed for six days prior to competition. It requires the athlete to consume a 50% carbohydrate diet for the first three days and then increase to a 70% carbohydrate diet (or 4.5 grams per pound of body weight) for the last three days before competition. The athlete begins training at a high aerobic intensity; then training time is gradually reduced on successive days. What do the critics say?Some problems associated with the classic carbohydrate-loading diet include increased blood cholesterol and urea nitrogen levels, which may cause problems for people susceptible to heart disease, diabetes, or kidney disease. The glycogen depletion stage may cause vitamin and mineral depletion, ketosis, the loss of lean tissue, and a reduction in training capability leading to a negative effect on performance. Are there any groups or books associated with this diet?Nancy Clark’s Sports Nutrition Guidebook by Nancy Clark, RD. Campaign, IL: Human Kinetics, 1997. USDA Food and Nutrition Information Center: Fitness, Sports, and Sports Nutrition Sportscience, an interdisciplinary site for research on human physical performance BibliographyAhlborg B, Bergström J, Ekelund LG, Hultman E. Muscle glycogen and muscle electrolytes during prolonged physical exercise. Acta Physiol Scand 1967;70:129–42. Arnall DA, Nelson AG, Quigley J, et al. Supercompensated glycogen loads persist 5 days in resting trained cyclists. Eur J Appl Physiol 2007;99:251–6. Bergström J, Hermansen L, Hultman E, Saltin B. Diet, muscle glycogen and physical performance. Acta Physiol Scand 1967;71:140–50. Coleman E. Carbohydrate unloading: a reality check. The Phys Sportsmed 1997;25:125–9. Online: www.physsportsmed.com/issues/1997/02feb/carbo.htm Coggan AR, Coyle EF. Effect of carbohydrate feedings during high-intensity exercise. J Appl Physiol 1988;65:1703. Coggan AR, Coyle EF. Metabolism and performance following carbohydrate ingestion late in exercise. Med Sci Sports Exerc 1989;21:59. Costill DL. Carbohydrates for exercise: dietary demands for optimal performance. Int J Sports Med 1988;9:1–18. Coyle EF, Hagberg JM, Hurley BF, et al. Carbohydrate feeding during prolonged strenuous exercise can delay fatigue. J Appl Physiol 1983;55:230–5. Coyle EF, Coggan AR, Hemmert MK,et al. Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. J Appl Physiol 1986;61:165–72. Hawley JA, Schabort EG, Noakes TD, et al. Carbohydrate loading and exercise performance. An update. Sports Med 1997;24:73–81. Hatfield DL, Kraemer WJ, Volek JS, et al. The effects of carbohydrate loading on repetitive jump squat power performance. J Strength Cond Res 2006;20:167–71. Havemann L, West SJ, Goedecke JH, et al. Fat adaptation followed by carbohydrate loading compromises high-intensity sprint performance. J Appl Physiol 2006;100:194–202. Ivy JL, Katz AL, Cutler CL, et al. Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion. J Appl Physiol 1988;64:1480–5. Ivy JL, Lee MC, Brozinick JT, et al. Muscle glycogen storage after different amounts of carbohydrate ingestion. J Appl Physiol 1988;65(5):2018–23. Jacobs KA, Sherman WM. The efficacy of carbohydrate supplementation and chronic high-carbohydrate diets for improving endurance performance. Int J Sport Nutr 1999;9:92–115. Katch FI, McArdle WD. Introduction to Nutrition, Exercise, and Health, 4th edition. Chapter 10, Optimal nutrition for exercise and good health. Philadelphia, PA: Lea & Febiger, 1993, 149–68. Reed MJ, Brozinick JT, Lee MC, et al. Muscle glycogen storage postexercise: effect of mode of carbohydrate administration. J Appl Physiol 1989;66:720–6. Roberts KM, Noble EG, Hayden, DB, et al. Simple and complex carbohydrate-rich diets and muscle glycogen content of marathon runners. Eur J Appl Occup Physiol 1988;57:70–4. Sherman WM, Peden MC, Wright DA,. Carbohydrate feedings 1 hr before exercise improves cycling performance. Am J Clin Nutr 1991;54:866–70. Sherman WM, Costill DL, Fink WJ, et al. Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. Int J Sports Med 1981;2:114–8. Sherman WM, Brodowicz G, Wright DA, et al. Effects of 4 h preexercise carbohydrate feedings on cycling performance. Med Sci Sports Exer 1989;12:598–604. Sherman WM, Wimer, GS. Insufficient dietary carbohydrate during training: does it impair performance? Int J Sports Nutr 1991;1:28–44. Walberg-Rankin J. Dietary carbohydrate as an ergogenic aid for prolonged and brief competitions in sport. Int J Sport Nutr 1995;5:S13–38 [review]. Whitley HA, Humphreys SM, Campbell,et al. Metabolic and performance responses during endurance exercise after high-fat and high-carbohydrate meals. J Appl Physiol 1998;85:418–24.  Copyright © 2007 Healthnotes, Inc. All rights reserved. www.healthnotes.com Learn more about Healthnotes, the company. Learn more about the authors of Healthnotes. The information presented in the Food Guide is for informational purposes only and was created by a team of US–registered dietitians and food experts. Consult your doctor, practitioner, and/or chemist for any health problem and before using any supplements, making dietary changes, or before making any changes in prescribed medications. Information expires September 2008. 2007-09-01 |
