Dietary Supplements and Sports Performance
At the 2004 Olympic games, athletes gave world record–breaking performances. Success at this level of sport competition is dependent primarily on genetic endowment of morphologic, psychologic, physiologic, and metabolic traits specific to a given sport, combined with superior training to optimize these traits. However, many athletes attempt to go beyond their endowments and training and use various techniques and substances, particularly nutritional strategies, in attempts to gain a competitive advantage.
In general, a diet that is optimal for health is also optimal for sports performance. A diet rich in fruits, vegetables, whole grains, lean meats, and low-fat dairy products that stresses variety, balance, and moderation will provide an adequate intake of carbohydrate, essential fatty acids, protein, vitamins, minerals, and water necessary to prevent a nutrient deficiency that could impair performance.
Sports supplements account for almost 10% of dietary supplements sold in the United States. In a 2000 joint statement, the American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada indicated that dietary supplements might be required by some athletes, such as those in weight-control sports. However, depending on the specific requirements of a given sport, some sports supplements may be used in attempts to enhance performance.
Sports supplements may be classified in four categories. Here’s an example of each:
• Supplements that perform as claimed. Creatine, as creatine monohydrate, is one of several supplements that can enhance performance. Creatine supplementation has been shown to increase muscle supplies of creatine phosphate (PCr), a compound necessary for rapid ATP resynthesis during very high-intensity exercise. Numerous major reviews, including a meta-analysis and a monograph, support the effect of creatine supplementation to enhance performance in short-duration, high-intensity exercise tasks such as cycle ergometer sprint protocols, and sprint running. Combined with resistance training, it also consistently appears to increase muscle mass and muscle strength. Yet, long-term effects of taking creatine have not been established.
• Supplements that may perform as claimed. Glycerol, when mixed and consumed with water, may result in greater fluid retention that may increase plasma volume and total body water, with potential beneficial effects for performance and temperature regulation during exercise in the heat. Research findings are inconsistent, but several well-controlled studies have found that glycerol hyperhydration may improve cardiovascular responses, temperature regulation, and cycling exercise performance under warm/hot environmental conditions. Reviewers differ as to whether glycerol supplementation enhances sports performance, and additional research is needed to resolve the equivocal findings.
• Supplements that do not perform as claimed. Ginseng contains a wide variety of chemical substances, some theorized to enhance sports performance by various means. Some early research indicated that ginseng supplementation could enhance sports performance, but these studies employed improper research methodology. Contemporary studies and comprehensive reviews overwhelmingly indicate that ginseng supplementation has no beneficial effect on cardiovascular, metabolic, or psychologic responses to either submaximal or maximal exercise performance, or on maximal performance capacity.
• Supplements that have been banned. Ma huang is herbal ephedrine, an ingredient which has been associated with significant health risks, such as hypertension, tachycardia, and death. Ephedrine use is prohibited by the World Anti-Doping Agency (WADA) and the National Collegiate Athletic Association (NCAA).
Most sports supplements do not improve performance, but some may. However, individuals may respond differently to various nutritional strategies or dietary supplements, so athletes and their advisors must be prepared to individualize a dietary regimen to optimize both training and performance. Most sports supplements are safe and permissible. However, excessive intake of many supplements, even vitamins, may pose significant health risks. The U.S. Anti-Doping Agency (USADA) and NCAA warn that dietary supplements, transdermal patches, and topical creams may contain prohibited substances, and that athletes are at risk of testing positive for banned substances and thus committing a doping violation.
Athletes will benefit most from consumption of a balanced and varied healthful diet.
by ROGER CLEMENS, Dr.P.H.
Director, Analytical Research
Professor, Molecular Pharmacology & Toxicology
USC School of Pharmacy, Los Angeles, Calif.
by MELVIN H. WILLIAMS, PH.D.
Fellow, American College of Sports Medicine
Eminent Scholar Emeritus
Dept. of Exercise Science
Old Dominion University, Norfolk, Va.