Going the Distance

Nutrition for Endurance Athletes

By James Gerber, DC

Healthnotes Newswire (March 16, 2000)?As warm weather returns this spring, many sports enthusiasts are planning to increase their athletic activity. Aside from training, nutrition may be the most important influence on athletic performance.1 However, in seeking a competitive edge, athletes are often susceptible to fad diets or supplements that have not been scientifically validated. Nevertheless, useful research exists to guide the exerciser toward optimum health and performance.

Endurance performance is vital to many sports, including long distance running, swimming, and cycling, as well as team sports such as basketball and soccer. Sports nutrition research has explored dietary practices and nutrition supplements for their usefulness to the endurance athlete.

Body fat

Despite an almost universal obsession among athletes with lowering body fat and increasing muscle mass, endurance athletes should not attempt to lower their body fat to extreme levels. Because body fat stores are necessary to support energy needs during longer exercise sessions, an athlete who is too lean may find his or her long-term performance compromised.2 The natural levels of body fat that result from regular training and a good diet are usually ideal for the individual athlete.

Speaking of diet, carbohydrates are the most efficient fuel for energy production and can be stored in the muscles and liver as a readily available energy source for prolonged, strenuous exercise. For these reasons, carbohydrates may be the most important nutrient for endurance sports performance.3 Emphasizing grains, starchy vegetables, fruits, low-fat dairy products, and carbohydrate-replacement beverages and reducing intake of fatty foods result in a relatively high carbohydrate diet that will ensure adequate availability of this energy fuel.

Carbohydrate-containing beverages satisfy fluid as well as energy needs of the exercising athlete. These beverages should be consumed during endurance training or competition (30?70 grams of carbohydrate per hour) as well as after exercise (40?60 grams of carbohydrate, repeating this intake every hour for at least five hours after the end of the exercise session). This will prevent carbohydrate depletion near the end of endurance training and help support the replenishment of spent energy stores in time for the next day's efforts.4 5 High-fat diets, recently popular among some endurance athletes, have not been found useful in most studies, and may even impair performance.6 7

Vitamins and minerals

A variety of vitamins and minerals are important for energy production; but that doesn?t mean more is necessarily better in terms of athletic performance. Many athletes consume a great deal of calories to support a strenuous training regimen; consequently, they get plenty of micronutrients (vitamins, minerals and amino acids) from their diet and don?t benefit from vitamin or mineral supplements.8 9 10 Only those who restrict their diet while exercising regularly are risking nutritional deficiencies that could affect performance. Even the electrolyte minerals sodium, chloride, potassium, and magnesium, which are lost in sweat, do not generally become low enough to cause problems unless exercise is continued for several hours in hot and humid weather.11 Only under those extreme conditions is it necessary for fluid and carbohydrate replacement beverages to contain electrolytes.

Sore muscles are a frequent consequence of starting up an increased regimen of exercise. Controlled research has suggested that taking vitamin C supplements, at least 400 mg per day, before and during the first few days of exercising, may reduce post-exercise muscle pain.12 13 However, no research has shown measurable improvements in endurance from taking supplements of vitamin C or from most other vitamins, unless a deficiency exists. One exception may be vitamin E in amounts of 400 IU (International Units) per day, which has demonstrated some ability to support aerobic exercise at high altitudes.14

In the realm of minerals, deficiencies of iron and magnesium can impair endurance, but most athletes have adequate diets that supply enough of these minerals.15 Some athletes who are experiencing fatigue may be anemic, however, and should be tested for iron deficiency. And, even iron deficiency that is not severe enough to cause anemia can impair performance via a reduction in the activity of iron-dependent enzymes. Typical magnesium supplements have not been found useful for enhancing an athlete?s endurance.16 However, a form of magnesium known as magnesium orotate was found in a double-blind study to improve swimming, cycling, and running times in triathletes who took about 5,000 mg per day of the compound.17

Other supplements

Many popular supplements, such as creatine monohydrate and androstenedione, have no effect on aerobic-exercise capacity. (This topic will be addressed in next week's Newswire feature article.) Caffeine, present in many popular beverages, affects the utilization of fat during exercise and has been shown to enhance endurance in many studies.18 19 However, caffeine may not work equally well for all athletes and can produce side effects of nervousness and gastrointestinal upset. Most research has used supplements of caffeine rather than coffee; coffee drinking was not effective in one recent study.20 Finally, excessive caffeine consumption has been banned by the International Olympic Committee.

Branched-chain amino acids (BCAAs) can be used to produce energy in muscle cells. Therefore, some people have suggested that supplementing with these amino acids might help exercise performance. However, most research has shown that BCAAs do not enhance endurance in athletes,21 although one controlled study did find that BCAA-supplemented drinks significantly prolonged cycling endurance in a hot climate.22

L-carnitine is a substance naturally produced in the body that plays a role in the conversion of fat to energy. Although sports nutrition scientists suspected that L-carnitine supplements might improve aerobic exercise performance, results of controlled studies have been disappointing.23

Strenuous physical activity is known to lower blood levels of coenzyme Q10, another substance made in the body that plays a role in energy production. However, a confusing body of research suggests that supplements of coenzyme Q10 can either improve exercise performance,24 harm performance,25 26 or have no effect at all.27

Some popular supplements are based on sound theories and known mechanisms of energy production, but often these speculations are not validated when put to the test in controlled research. This is true for most endurance studies on such sports nutrition products as aspartate,28 medium-chain triglycerides (MCT),29 octacosanol,30 beta hydroxy-beta-methylbutyrate (HMB),31 phosphate-loading,32 and inosine.33

In summary, many frequently used sports supplements have questionable value to the endurance athlete, with the exception of caffeine and certain others in special situations. On the other hand, sports nutrition research has confirmed the value of a high carbohydrate diet with liberal use of fluid- and carbohydrate-replacement beverages during intensive training.

References

1. American Dietetic Association: Position of the American Dietetic Association and the Canadian Dietetic Association: Nutrition for physical fitness and athletic performance for adults. J Am Diet Assoc 1993;93:691?6.
2. McArdle WD, Katch FI, Katch VL. Sports & Exercise Nutrition. Chapter 12, Body composition assessment and sport-specific observations. Philadelphia, PA: Lippincott, Williams & Wilkins, 1999.
3. 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].
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10. Weight LM, Myburgh KH, Noakes TD. Vitamin and mineral supplementation: effect on the running performance of trained athletes. Am J Clin Nutr 1988;47:192?5.
11. Pivarnik JM, Palmer JM. Water and electrolyte balance during rest and exercise. In: Wolinsky I, Hickson JF, eds. Nutrition in Exercise and Sport, 2nd ed. Boca Raton: CRC Press, 1994:245?63 [review].
12. Jakeman P, Maxwell S. Effect of antioxidant vitamin supplementation on muscle function after eccentric exercise. Eur J Appl Physiol 1993;67:426?30.
13. Kaminski M, Boal R. An effect of ascorbic acid on delayed-onset muscle soreness. Pain 1992;50:317-21.
14. Simon-Schnass I, Pabst H. Influence of vitamin E on physical performance. Int J Vitam Nutr Res 1988;58:49?54.
15. Nielsen P, Nachtigall D. Iron supplementation in athletes. Current recommendations. Sports Med 1998;26:207?16.
16. Weller E, Bachert P, Meinck HM, et al. Lack of effect of oral Mg-supplementation on Mg in serum, blood cells, and calf muscle. Med Sci Sports Exerc 1998;30:1584?91.
17. Golf SW, Bender S, Gruttner J. On the significance of magnesium in extreme physical stress. Cardiovasc Drugs Ther 1998;12(Suppl 2):197?202.
18. Applegate E. Effective nutritional ergogenic aids. Int J Sport Nutr 1999;9:229?39.
19. Tarnopolsky MA. Caffeine and endurance performance. Sports Med 1994;18:109?25 [review].
20. Graham TE, Hibbert E, Sathasivam P. Metabolic and exercise endurance effects of coffee and caffeine ingestion. J Appl Physiol 1998;85:883?9.
21. Wagenmakers AJ. Amino acid supplements to improve athletic performance. Curr Opin Clin Nutr Metab Care 1999 Nov;2(6):539?44 [review].
22. Mittleman KD, Ricci MR, Bailey SP. Branched-chain amino acids prolong exercise during heat stress in men and women. Med Sci Sports Exerc 1998;30:83?91.
23. Heinonen OJ. Carnitine and physical exercise. Sports Med 1996;22:109?32 [review].
24. Bucci L. Nutrients as Ergogenic Aids for Sports and Exercise. Boca Raton: CRC Press, 1993, 54?7 [review].
25. Malm C, Svensson M, Ekblom B, et al. Effects of ubiquinone-10 supplementation and high intensity training on physical performance in humans. Acta Physiol Scand 1997;161:379?84.
26. Laaksonen R, Fogelholm M, Himberg JJ, et al. Ubiquinone supplementation and exercise capacity in trained young and older men. Eur J Appl Physiol 1995;72:95?100.
27. Overvad OK, Diamant B, Holm L, et al. Efficacy and safety of dietary supplementation containing Q10. Ugeskr Laeger 1997;159:7309?15 [review] [in Danish].
28. Wesson M, McNaughton L, Davies P, et al. Effects of oral administration of aspartic acid salts on the endurance capacity of trained subjects. Res Quart Exer Sport 1988;59:234?6.
29. Berning JR. The role of medium-chain triglycerides in exercise. Int J Sport Nutr 1996;6:121-33 [review].
30. Saint-John M, McNaughton L. Octacosanol ingestion and its effects on metabolic responses to submaximal cycle ergometry, reaction time and chest and grip strength. Int Clin Nutr Rev 1986;6(2):81?7.
31. Vukovich MD, Adams GD. Effect of beta-hydroxy beta-methylbutyrate (HMB) VO2 peak and maximal lactate in endurance trained cyclists. Med Sci Sports Exerc 1997;29:S252 [abstract].
32. Galloway SD, Tremblay MS, Sexsmith JR, et al. The effects of acute phosphate supplementation in subjects of different aerobic fitness levels. Eur J Appl Physiol 1996;72:224?30.
33. Williams MH, Kreider RB, Hunter DW, et al. Effect of inosine supplementation on 3-mile treadmill run performances and VO2 peak. Med Sci Sports Exerc 1990;22:517?22.

See part 2 of this Newswire article next week for a discussion of the possible benefits of these and other supplements on strength and sprint performance.

James Gerber, DC, is the Scientific Editor for the Healthnotes Online database, an exclusive product of Healthnotes, Inc. Dr. Gerber is Associate Professor of Clinical Sciences at Western States Chiropractic College in Portland, Oregon and teaches post-graduate courses for several other colleges. Dr. Gerber is the author of Handbook of Preventive and Therapeutic Nutrition (Aspen, 1992) and a contributor to Conservative Management of Sports Injuries (Williams & Wilkins, 1997).

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