Sports nutrition is a broad interdisciplinary field that focuses on the science behind and application of proper nutrition during exercise, with areas of interest including the body's use of nutrients during athletic competition; the need, if any, for nutritional supplements among athletes; and the role of proper nutrition and dietary supplements in enhancing an athlete's performance. The psychological dimension of sports nutrition is concerned with eating disorders and other psychiatric conditions related to nutrition among athletes.
Professionals in the field of sports nutrition include dietitians, biochemists, exercise physiologists, cell and molecular biologists, and occasionally psychotherapists. Some people who specialize in the field of sports nutrition are registered dietitians (RDs) who have completed a master's or other advanced degree in the field of exercise physiology. Most academic sports nutritionists, however, hold doctoral degrees in the field of exercise physiology and often specialize in working with athletes in one particular 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 work primarily with team sports, endurance sports (such as cycling, long-distance running, and triathlon training), or sports involving weight training (e.g., wrestling, weight-lifting, and some forms of bodybuilding). Some athletes may also wish to work one-on-one with a sports nutritionist.
Many athletes utilize good nutrition to promote strong athletic performance. A balanced diet and proper hydration help fulfill the body's energy requirements, resulting in optimal performance whether for endurance, power, or strength. The need for adequate nutrition holds true both for training necessary before events and for the events themselves. Both amateur and professional athletes alike can benefit from good nutrition.
More specifically, sports nutrition can be used to:
Specific aspects of sports nutrition include hydration, assessment of energy needs, assessment of weight and body composition, strategies for weight change, timing of meals, and the use of ergogenic aids.
Fluid intake guidelines
Time in reference to event
Ounces of fluid (oz.)
24 hours before
4 hours before
At least 16-20 oz. water
10-15 minutes before
8-12 oz. water
During (less than 60 min.)
3-8 oz. of water every 15-20 min.
During (longer than 60 min.)*
3-8 oz. of sports drink every 15-20 min.
20-24 oz. fluid for every lb. lost
*Do not consume more than 32 oz. in one hour.
SOURCE: Simpson, Michael R. and Tom Howard, M.D. “Selecting and Effectively Using Hydration for Fitness.” American College of Sports Medicine, 2011. http://www.acsm.org/docs/brochures/selecting-and-effectively-using-hydration-for-fitness.pdf?sfvrsn=2 (accessed April 1, 2018).
Sweating during athletic activity results in the loss of water and sodium, making hydration, or maintaining a proper level of fluid in the body, an important aspect of sports nutrition. Dehydration can result in decreased 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 two to three 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 (substances that increase urine output) is dangerous in athletes.
People vary in their rate of fluid output, and a health professional is the best person to evaluate individual athletes and determine how much fluid is needed after exercise or training. The most common way to do so 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. According to the American College of Sports Medicine, this equates to 16–24 ounces of fluid for each pound (0.5 kg) of body weight lost.
If the workout is lengthy or intense, good hydration is more effectively maintained by consuming sports drinks or other beverages that contain salt and carbohydrates than by drinking plain water. Sports drinks are isotonic; that is, they contain the same proportion of electrolytes and carbohydrates to fluid as the human body. After exercise, the body requires carbohydrates to replace the glycogen (a complex sugar) stored in muscle tissue and the liver. When consumed, carbohydrates break down into glucose, a simple sugar that provides energy. Excess glucose is stored as glycogen, which serves as a reserve energy source during intense exercise. If these reserves are depleted, the body will start to tire; long-distance runners, for example, who deplete their stores of glycogen may experience fatigue to the point of being unable to move. In addition to the risk of glycogen depletion, drinking excessive amounts of water without replacing sodium may put the athlete at risk of water intoxication, a potentially fatal condition that occurs when the sodium lost through sweat is not replaced. The resulting electrolyte imbalance affects the brain and central nervous system. Blood plasma sodium levels below 100 millimoles per liter (mmol/L) (2.3 grams per liter [g/L]) frequently result in swelling of the brain tissue, coma, and even death.
Athletes usually require a higher level of calorie intake than nonathletes, although the amount varies depending on an athlete's age, gender, height, weight, body composition, stage of growth, level of fitness, and type of exercise, taking into account the activity's intensity, frequency, and duration. An appropriate diet for most athletes consists of a minimum of 2,000 calories per day: 55%–65% should come from carbohydrates, 15%–20% from protein, and 20%–30% from fats.
The body mass index (BMI) is a formula that uses a person's height-to-weight ratio to determine whether he or she is at a healthy weight. Use of the BMI to evaluate athletes' weights is not recommended, because many have a high proportion of muscle tissue to fat and, because muscle is more dense than fat, may therefore be considered “overweight” by standard body mass charts. For young athletes, it is better to check whether the child or young adult up to age 20 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, available online at http://www.cdc.gov/growthcharts/html_charts/wtstat.htm .
Athletes in any age group desiring to lose or gain weight need to be properly supervised by an RD as well as a physician, because unhealthful dietary practices can lead to long-term problems. The American Academy of Pediatrics (AAP) offers the following recommendations for weight change in young athletes, though the advice is sound for athletes of any age:
WEIGHT LOSS. Weight loss programs are sometimes recommended for athletes in weight-sensitive sports, most often for wrestling, judo, jockeying, figure skating, gymnastics, long-distance running, rowing, and swimming. Unfortunately, many people adopt unhealthful eating or exercise patterns to keep their weight down. The AAP advises that young athletes (younger than the ninth grade) not be put on weight loss regimens to improve athletic performance, due to the risk of developing unhealthy or obsessive eating behaviors.
Restricting food intake is the most common method of weight loss among athletes, but some athletes may also engage in purging (self-induced vomiting plus abuse of laxatives and diuretics), fasting, compulsive exercising, stimulant use, or the use of such gadgets as sauna suits. Some studies have shown that as many as 11% of wrestlers and 15% of swimmers meet the criteria for eating disorders.
Unhealthful weight-loss practices are dangerous and unbeneficial; much of the weight lost will be lean muscle rather than fat, which can affect athletic performance. Females 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. 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.
WEIGHT GAIN. Athletes in sports requiring strength or power (such as football, rugby, basketball, and bodybuilding) may try to gain weight 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 hypertension (high blood pressure), cardiovascular (heart) disease, and type 2 diabetes. It is important for athletes to recognize the genetic limitations associated with their body build, as people who are naturally slender cannot add as much muscle tissue to their bodies as those who are built more solidly.
Consuming foods and fluids before exercising helps ensure peak performance. Meals provide the muscles with glucose to sustain energy during physical activity. Fluid levels should also be increased before engaging in activity to ensure adequate hydration. Under normal circumstances, athletes should drink plenty of fluids throughout the day and consume sufficient fluids before, during, and after strenuous activities. The composition of preworkout meals or snacks should be high-carbohydrate and low-fat foods, as carbohydrates are quickly converted to glucose, providing the best source of energy. For strength workouts, a small amount of protein may be included as well. Large meals should be consumed at least three to four hours before exercise. For smaller meals, such as snacks, only one to two hours is necessary.
The same principles apply to post-workout meals and snacks. After a high-intensity workout, the body's glycogen stores need to be replenished. According to the American Council on Exercise, good post-work out snacks include high-glycemic, easily digested carbohydrates paired with protein. High-glycemic carbohydrates, such as refined grains, are converted to glucose more quickly than low-glycemic carbohydrates, such as whole grains, which take longer to digest. The spike in glucose replenishes the body's supply and promotes recovery. It is important to note, however, that the majority of carbohydrates consumed in the diet should be whole grain, and that only people engaging in long or high-intensity workouts, such as athletes, need the added benefits of a high-glycemic snack. Most people will benefit from a snack containing a mix of wholegrain carbohydrates and protein. Endurance athletes may need to eat during their workouts to maintain their energy.
Ergogenic aids are drugs or dietary supplements taken to improve athletic performance or endurance by providing energy or adding muscle tissue. Types of ergogenic aids include anabolic or androgenic steroids (male sex hormones), steroid precursors, growth hormone, beta-alanine, caffeine, and creatine (an organic acid stored in the body that supplies energy to muscle cells). Ephedra, an herb used in traditional Chinese medicine, was previously a popular ergogenic aid in the United States, but it was banned by the U.S. Food and Drug Administration (FDA) in April 2004 due to adverse effects and deaths.
Medical and nutritional professionals are concerned about the use of ergogenic aids. These drugs and supplements, first used by adult athletes in the 1980s, are now being used by children as young as 10 or 12 years of age. Creatine and anabolic steroids may produce long-term adverse effects on the body, and steroid precursors and growth hormones pose a good many risks to health without any proof that they actually enhance athletic performance. The Academy of Nutrition and Dietetics advises consumers to exercise caution when purchasing and using ergogenic aids, as many supplements boast unproven claims that are not supported by the FDA. The Academy's most recent warnings about unproven claims concern pyruvate, claimed to promote weight loss; chromium picolinate, claimed to change body composition; and beta-alanine, claimed to boost muscle performance.
No magic food or supplement can enhance athletic performance. Rather, the benefits of such healthful habits as eating nutritious foods, drinking plenty of water, getting enough sleep, and avoiding drugs and harmful substances combine to support improved performance. Eating the right foods and consuming enough fluids will help athletes train harder and compete at their best. Consultation with a qualified sports nutritionist may be useful for anyone heavily involved in a sport, whether amateur or professional. The consultation should be individualized, as people vary in their energy needs, and what works well for one athlete may not be right for another.
Symptoms of the female athlete triad include missing three or more menstrual periods, experiencing an unusual number of stress fractures, spending an excessive amount of time working out, wearing baggy or concealing clothes even in warm weather, and demonstrating patterns of restricted eating. The condition is most common in activities that place an emphasis on weight or body composition, such as gymnastics, figure skating, and cross country running. Any female athlete who stops having menstrual periods (amenorrhea) or has only scanty periods (oligomenorrhea) should be evaluated for disordered eating or overexercising.
Doping in sports refers to the practice of taking anabolic steroids and other substances forbidden by international sports organizations. 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 erythropoietin (EPO) 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.
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. The sudden adoption of a vegetarian or vegan diet in an athlete who was previously eating meat and fish may sometimes indicate the onset of an eating disorder.
Athletes should not take any dietary supplement without consulting their physician and a registered dietitian. Some herbal dietary supplements used by athletes are known to interact with prescription medications. These include:
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, their pharmacist, and a nutritionist.
No complications are associated with nutritional monitoring of athletes by qualified professionals. The AAP, however, recommends seeking nutritional information and assessment from dietetic professionals, not from team coaches or personal trainers. For adults, detailed information about such topics as nutrient timing, body composition, protein intake, and exercise can be obtained from the International Society of Sports Nutrition (ISSN) position papers.
Parents of young children should be aware of the ways in which children's hydration requirements during athletic activity differ from those of adults. Young children are more susceptible to heat-related illnesses than adults during exercise for several reasons:
Children with such chronic medical conditions as diabetes or obesity, those who take medications for attention-deficit hyperactivity disorder, and those who have recently recovered from any illness involving fever or such symptoms as vomiting and diarrhea are at increased risk of heat-related distress. These children require very careful monitoring for hydration and body temperature regulation.
Young adults may also be at risk of developing eating disorders or unhealthy dieting practices. Parents of adolescents who are heavily involved in sports should familiarize themselves with the signs of disordered eating. Children and adolescents especially need to take in enough calories and nutrients, as their bodies are still growing and developing. Restricting dietary intake at a young age may cause health problems later in life.
See also Body mass index ; Calories ; Carbohydrates ; Dehydration ; Dietary supplements ; Eating disorders ; Electrolytes ; Ephedra ; Ergogenic aids ; Hydration .
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Rebecca J. Frey, PhD