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Sports nutrition is a broad interdisciplinary field that involves dietitians, biochemists, exercise physiologists, cell and molecular biologists, and occasionally psychotherapists. It has both a basic science aspect that includes such concerns as understanding the body's use of nutrients during athletic competition and the need for nutritional supplements among athletes; and an application aspect, which is concerned with the use of proper nutrition and dietary supplements to enhance an athlete's performance. The psychological or psychiatric dimension of sports nutrition is concerned with eating and other mental disorders related to nutrition among athletes.
Some persons who specialize in the field of sports nutrition are registered dietitians (RDs) who have pursued a master's or other advanced degree in the field of exercise physiology; the American Dietetic Association (ADA) has a dietetic practice group or DPG for sports nutritionists called Sports, Cardiovascular, and Wellness Nutritionists (SCAN), which has its own website and telephone contact number. Most academic sports nutritionists, however, hold doctoral
Recommended fluid intake for athletes. (Illustration by GGS Information Services/Thomson Gale.)
degrees in the field of exercise physiology and often specialize in working with athletes in one particular type of sport, such as baseball or swimming. Although sports nutrition can be applied to almost any form of athletic training or physical activity—including yoga, tai chi, martial arts, and professional dance—professional sports nutritionists do most of their work with team sports, endurance sports (cycling, long-distance running, triathlon training, etc.) or sports involving weight training (wrestling, weight-lifting, some forms of bodybuilding). Some nutritionists also work one-on-one with individual athletes.
Sports nutrition has several purposes:
Hydration, or maintaining a proper level of fluid in the body, is an important aspect of sports nutrition because of the loss of water and sodium through sweating during athletic activity. Dehydration results in loss of muscle strength, difficulty concentrating, irritability, and headache. An adult who has lost more than 8% of
initial body weight through sweating without replacing the lost fluid is at risk of heat cramps, heat exhaustion, and heat stroke. Moreover, dehydration may be progressive in athletes who do not replace fluid loss overnight; the greater the loss of body fluid, the longer it takes to rehydrate the body. When dehydration has taken place over 2 to 3 days, it will take a minimum of 48 hours to replace the fluids in body tissues. The health risks of dehydration are a major reason why abuse of diuretics is dangerous in athletes.
People vary in their sweating rates; therefore, health professionals must evaluate athletes on an individual basis to determine how much fluid is needed after exercise or training. The most common way to measure this need is to weigh the athlete before and after exercise; the amount of weight lost should be replaced with an equal amount of fluid before the next workout. The usual rule of thumb is 1 pint of fluid containing carbohydrates and electrolytes for each pound of weight loss.
Assessment of energy needs
Athletes usually require a higher level of calorie intake than nonathletes, although the amount varies depending on the athlete's sex, age, height, weight, body composition, stage of growth, level of fitness, and the intensity, frequency, and duration of physical exercise. An appropriate diet for most athletes consists of a minimum of 2000 calories per day; 55–65% should come from carbohydrates, 15–20% from protein, and 20–30% from fats.
Assessment of weight and body composition
The use of the body mass index (BMI) to evaluate athletes’ weight is not recommended because many have a high proportion of muscle tissue to fat and may therefore be considered “overweight” by standard body mass charts. A better reference guide is to check whether the athlete falls between the 25th and the 75th percentile of weight for height by age, measured according to the National Center for Health Statistics (NCHS) guidelines.
Well-nourished athletes should have a lean muscle mass above the 25th percentile, although the ideal ratio of lean muscle to body fat has not yet been established for any sport. Male athletes, however, should not have less than 7% body fat. There are several methods for estimating the proportion of body fat on an athlete's body: underwater weighing (equipment is expensive and limited in availability); skinfold measurements taken by high-precision calipers on three to five sites on the right side of the body (the right side is always used even if the athlete is left-handed); bioelectrical impedance analysis or BIA (a technique that measures body composition by passing a small electrical current through the body and measuring the resistance of various body tissues, as lean muscle contains a higher proportion of water than fat); and computerized calipers.
Strategies for weight change
It is important for athletes in any age group needing or desiring to lose or gain weight to be properly supervised by a nutritionist as well as a physician, because unhealthful dietary practices can lead to long-term mental as well as physical disorders. The American Academy of Pediatrics (AAP) makes the following recommendations for weight change in young athletes:
WEIGHT LOSS. Weight loss programs are sometimes recommended for athletes in weight-sensitive sports, most often wrestling or judo for boys and figure skating, gymnastics, long-distance running, rowing, and swimming for girls. Unfortunately, many young people go too far in adopting unhealthful eating or exercise patterns in order to keep their weight down. Because of this tendency, the AAP states that children younger than the ninth grade should not be put on weight-loss regimens to improve athletic performance.
Restricting food intake is the most common method of weight loss among athletes, but a large percentage of young athletes also engage in purging (self-induced vomiting plus abuse of laxatives and diuretics), fasting, or the use of stimulants, wet suits, sauna baths, or compulsive exercising. Some studies have shown that as many as 11% of wrestlers meet the criteria for eating disorders, and 15% of swimmers.
Unhealthful weight loss practices are dangerous because much of the weight lost will be lean muscle rather than fat, which can affect athletic performance. Girls who develop eating disorders or body dysmorphic disorder are at risk of developing the so-called female athlete triad, which consists of disordered eating, cessation of menstrual periods (amenorrhea), and osteoporosis or brittle bones. A common symptom associated with the triad is an unusually high number of stress fractures during the girl's athletic career. The triad, which was first described in 1993, may have long-term consequences for a woman's health. Female athletes in their freshman year of college are reported to be at increased risk of developing the triad, particularly if it is their first experience of living away from home or they are having academic difficulties.
WEIGHTGAIN. Athletes in sports requiring strength or weight lifting (football, rugby, basketball, bodybuilding) may try to gain weight in order to build the body's muscle mass. Inappropriate methods, however, will lead to gaining fat rather than muscle, putting the athlete at risk in midlife for high blood pressure, cardiovascular disease, and type 2 diabetes. It is important for athletes to recognize the genetic limitations related to their body build, as persons who are naturally slender cannot add as much muscle tissue to their bodies as those who are built more solidly.
The safest way to gain weight and build muscle tissue is to consume 1.5 to 1.75 grams of protein per kilogram of body weight per day and participate in strength training. The most effective form of strength training is thought to be multiple sets of weight lifting with a relatively high number of repetitions (8–15) per set. Athletes should avoid the use of dietary supplements in building muscle, particularly steroids, which have been shown to be harm-fultohealthinboth males and females.
Use of ergogenic aids
Ergogenic aids are drugs or dietary supplements taken to improve athletic performance or endurance by providing energy or adding muscle tissue. The most common ergogenic aids used are anabolic or andro-genic steroids (male sex hormones), steroid precursors, growth hormone, creatine (an organic acid stored in the body that supplies energy to muscle cells), and ephedra, an herb sometimes called by its Chinese name, ma huang. Some ergogenic aids are illegal to use in competition.
Medical and nutritional professionals are concerned about the use of ergogenic aids among young athletes for two major reasons. The first is that these drugs and supplements, first used by adult athletes in the 1980s, are now being used by children as young as 10 or 12. The second is that creatine and anabolic steroids may produce long-term adverse effects on the body even though they do produce gains in body mass and strength, while steroid precursors, ephedra, and growth hormone pose a good many risks to health without any proof that they enhance athletic performance.
The ADA's position statement says, “Nutritional ergogenic aids should be used with caution, and only after careful evaluation of the product for safety, efficacy, potency, and whether or not it is a banned or illegal substance.”
Consultation with a qualified sports nutritionist is a sound practice for anyone in any age group who is heavily involved in any sport, whether amateur or professional. Specific precautions:
Some herbal dietary supplements used by athletes are known to interact with prescription medications, such as St. John's wort (Hypericum perforatum) and ephedra (Ephedra sinica), often used to promote weight loss; valerian (Valeriana officinalis),often taken for insomnia; cayenne (Capsicum frutescens), ginseng (Panax ginseng), and cordyceps (Cordyceps sinensis), taken internally to increase carbohydrate metabolism or increase endurance; and Siberian ginseng (Eleutherococcus senticosus) and echinacea (Echinacea angustifolia), taken to boost the immune system. Some of these drug interactions are potentially serious. Athletes should not take any herbal remedies, including those marketed specifically to athletes, without consulting their physician and a nutritionist.
There are no complications associated with nutritional monitoring of athletes by qualified professionals. The AAP, however, recommends seeking nutritional information and assessment from dietetics professionals, not from team coaches or personal trainers.
Parental concerns about sports nutrition are age-related in most cases. Parents of young children should be aware of the ways in which children's hydration requirements during athletic activity differ from those of adults. Parents of adolescents who are heavily involved in sports should acquaint themselves with the signs of unhealthy eating or dieting practices in high school or college-age athletes.
Hydration needs in young children
Young children are more susceptible to heat-related illnesses than adults during exercise for several reasons: they produce more heat relative to body mass for the same intensity of exercise; they have a lower cardiac output than adults at any exercise level; they have a higher threshold for rise in body temperature before beginning to sweat; and they have a lower sweating capacity than adults, which makes it harder for them to dissipate body heat through evaporation. Children also have a less efficient thirst mechanism than adults, which means that they are more likely to become dehydrated during exercise because they do not feel as intense a need to drink liquids. Orange- or grape-flavored drinks are often a good way to rehydrate children because they will increase their fluid intake when the beverage is flavored.
Female athlete triad
Parents should watch for indications of the female athlete triad, such as missing three or more menstrual periods; an unusual number of stress fractures; an excessive amount of time spent exercising or working out; a tendency to wear baggy or concealing clothes even in warm weather; and a restricted eating pattern. Adopting a vegetarian or vegan diet may indicate the onset of an eating disorder in a female athlete.
Doping in sports refers to the practice of taking anabolic steroids and other substances forbidden by international sports organizations. The word is derived from the Dutch word for an alcoholic drink consumed by Zulu warriors to give them energy before a battle. In the early twentieth century, doping referred primarily to the illegal drugging of race horses, but has been applied to human athletes since the 1920s.
In the 1970s, testing of athletes’ blood samples focused largely on steroid use, but in the 1980s and 1990s, new tests had to be devised to detect evidence of blood doping. Blood doping refers to the use of blood transfusions or a hormone called erythropoetin (EPO) in order to increase the level of hemoglobin in an athlete's blood, and therefore its oxygen-carrying capacity. The use of EPO in such endurance sports as marathon running or cycling increases the athlete's risk of heart disease if it is used to raise blood hemoglobin levels above 13.0 g/dL.
Newer forms of doping include the use of modafinil (Provigil), a drug ordinarily used to treat narcolepsy (a sleep disorder), and gene doping. Gene doping is defined by the World Anti-Doping Agency, an organization founded in 1999, as “the non-therapeutic use of cells, genes, genetic elements, or of the modulation of gene expression, having the capacity to improve athletic performance.” One possible technique of gene doping would be the use of a synthetic gene that could last for years and produce high amounts of naturally occurring muscle-building hormones.
Vegetarian and vegan diets
It is possible for an athlete to maintain strength and overall health on a vegetarian diet provided that a variety of plant-based sources of protein are consumed on a daily basis and energy intake is adequate. Vegetarian and especially vegan athletes are at risk of inadequate creatine and iron intake, however, as well as insufficient amounts of zinc, vitamin B12, vitamin D, and calcium. Iron deficiency will eventually affect athletic performance, as will low levels of creatine. Coaches and trainers should be aware that sudden adoption of a vegetarian or vegan diet in an athlete who was previously eating meat and fish may indicate the onset of an eating disorder.
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American Academy of Pediatrics (AAP). 141 Northwest Point Blvd., Elk Grove Village, IL 60007. Telephone: (847) 434-4000. Website:http://www.aap.org.
American College of Sports Medicine (ACSM). P. O. Box 1440, Indianapolis, IN 46206-1440. Telephone: (317) 637-9200. Website:http://www.acsm.org.
American Council on Exercise (ACE). 4851 Paramount Drive, San Diego, CA 92123. Telephone: (858) 279-8227. Website: htpp://www.acefitness.org.
American Dietetic Association (ADA). 120 South Riverside Plaza, Suite 2000, Chicago, IL 60606-6995. Telephone: (800): 877-1600. Website:http://www.eatright.org.
American Society of Health-System Pharmacists. 7272 Wisconsin Avenue, Bethesda, MD 20814. Telephone: (301) 657-3000. Website:http://www.ashp.org.
Dietitians of Canada/Les dietetistes du Canada (DC). 480 University Avenue, Suite 604, Toronto, Ontario, Canada M5G 1V2. Telephone: (416) 596-0857. Website:http://www.dietitians.ca.
Gatorade Sports Science Institute (GSSI). 617 West Main Street, Barrington, IL 60010. (800) 616-4774. Website:http://www.gssiweb.org. The GSSI website has a useful online library of over a hundred articles on various aspects of sports nutrition, training and performance, and sports medicine, including material on specific sports.
Herb Research Foundation (HRF). 4140 15th Street, Boulder, CO 80304. Telephone: (303) 449-2265. Website:http://www.herbs.org.
National Center for Health Statistics (NCHS). Telephone: (800) 311-3435. Website:http://www.cdc.gov/nchs/.
National Strength and Conditioning Association (NSCA). 1885 Bob Johnson Drive, Colorado Springs, CO 80906. Telephone: (800) 815-6826 or (719) 632-6722. Website:http://www.nsca-lift.org.
Sports, Cardiovascular, and Wellness Nutritionists (SCAN). SCAN is a dietetic practice group (DPG) of the American Dietetic Association. Telephone: (800) 249-2875 or (847) 441-7200. Website:http://www.scandpg.org.
U. S. Food and Drug Administration (FDA). 5600 Fishers Lane, Rockville, MD 20857-0001. Telephone: (888) INFO-FDA. Website: http://www.fda.gov/default.htm.
World Anti-Doping Agency (WADA). Stock Exchange Tower, 800 Place Victoria, Suite 1700, P.O. Box 120, Montreal, Quebec, Canada H4Z 1B7. Telephone (514) 904-9232. Website:http://www.wada-ama.org.
Rebecca J. Frey, PhD