Current issues in sports nutrition in athletes.
Sports nutrition encompasses several subjects including the energy, nutrient and fluid needs of athletes, assessment of body composition, strategies for weight change, special nutrient needs during training, competition, and recovery, and the use of supplements and nutritional ergogenic aids.
Active people require more energy to maintain lean tissue mass, for immune and reproductive function, and optimum athletic performance. Meeting calorie needs can be difficult for some athletes, especially in those sports where severe weight-loss practice and restricted intakes are common. When energy intake is limited, the body uses fat and lean tissues for energy, thus resulting in loss of strength and performance. Chronic undernutrition also places the athlete at risk for micronutrient deficiency. While there are recommended dietary allowances and activity factors for calculating calorie needs, the best indication that energy needs are being met is the athlete demonstrating maintenance of weight and body composition while training for a sport.
Protein, Carbohydrate, and Fat Needs in Athletes
Protein requirements are increased in athletes. Endurance athletes need 1.2 to 1.4 g/kg body mass per day. Resistance and strength-trained athletes need 1.6 to 1.7 g/kg body mass per day. This is compared with 0.8 to 1.0 g/kg body mass for nonathletes. For example, a 200-pound long distance runner would require approximately 118 g protein, while a 200-pound football player would need roughly 150 g. The nonathlete would only require about 75 g protein per day. (See Table for amount in protein found in food.)
Carbohydrate needs vary in athletes depending on overall energy needs, type of sport, and the sex of the athlete. Recommendations range from 6 to 10 g/kg body mass per day with the goals being maintenance of blood-glucose levels during exercise, and to replace muscle glycogen. In fact, replacing muscle glycogen is crucial for recovery from one training session to the next to maximize training gains. It is important to have nutritious carbohydrate snacks on hand immediately after training to initiate the re-fueling process. The following snacks are examples that provide sufficient carbohydrate to optimize recovery:
Male athlete (target 60-80 g carbohydrate).
* One 8-oz carton fruit yogurt + cereal bar + 8 oz of fruit juice
* 8 oz milk + cereal bar + 1 banana
* 32 oz sports drink
Female athlete (target 40-50 g carbohydrate).
* One 8 oz carton fruit yogurt + cereal bar or 1 banana
* 8oz milk + cereal bar
* 24 oz sports drink
Fat intake should also correspond with overall energy needs, with fat making up 20 to 25% of total energy consumed to provide essential fatty acids and fat-soluble vitamins (A, D, E, and K). There is no research to support recommending very-low-fat (<15%) or high-fat diets to athletes. An athlete requiring 3,000 calories daily should, therefore, consume at least 50 g fat (15% calories from fat). (See Table for fat content in foods.)
Research has clearly documented the beneficial effects of nutrition on physical performance. It is the position of both the American College of Sports Medicine (ACSM) and the American Dietetic Association (ADA) in particular, that physical activity, athletic performance and recovery from exercise are enhanced by optimal nutrition. During times of intense physical activity, energy and macronutrient needs must be met to maintain body weight, replenish glycogen stores, and provide adequate protein for building and repairing tissue. Carbohydrate, protein, and fat intake are all crucial to optimal performance. Athletes must be well-hydrated before exercise, and consume adequate liquid during and after performance to balance fluid loss. Appropriate selection of foods and fluids, the timing of intake, and supplement choices are important for optimal health and exercise performance.
Many athletes today rely on sports nutritionists to assist them in designing meal plans and eating strategies to give them a competitive edge. While each sport entails different training regimens and performance goals, it is clear that a proper diet can help any athlete reach their potential. Likewise, persistent fatigue, poor recovery, illness and unwanted weight loss are the most common result of undernutrition or suboptimal eating habits. The following is a small subset (not intended to be a representative or exhaustive list) of specific sports and common nutrition issues for each. It is the authors' goal to address as many specific issues as possible using a variety of sports played by both sexes.
Football is a game of speed, skill, and strength, all of which may be affected by the athlete's nutrition. Carbohydrate is needed to fuel hard working muscles; with 60 to 70% of calories coming from bread, cereal, rice, pasta, fruit, vegetables, and low-fat dairy products (about 2/3 of the plate at each meal).
Muscle bulk and strength. A high-energy (calorie) diet is the key to bulking up. Although protein is important, and football players need more than nonathletes, carbohydrate should be the primary energy source. Coaches and parents should encourage players to avoid skipping meals. Snack before practice and bring a post-training snack to eat in the locker room. Good choices are high carbohydrate foods such as crackers, fruit, or a bagel with a sports drink.
Recovery eating recommendations. The goal for recovery eating is to facilitate rapid recovery of muscle glycogen levels. Restoring these levels assures the athletes' energy fuel needs for the day are met. This strategy helps fight fatigue and build muscle mass in the gym. Players who fail to plan for long training sessions or road-trips often fail to replenish muscle glycogen stores. Under-nutrition can result in fatigue, especially late in the season, and struggles in the gym when attempting to increase muscle mass despite working hard.
Fluid needs. Players must be hydrated properly to avoid fatigue both on game day and during practice sessions. Sports drinks are recommended over water because they taste good, contain electrolytes, and may help prevent cramping. Players should be weighed before and after practice to be sure fluid losses are replaced. One pound should be replaced with at least 20 ounces of fluid. Players should be educated regarding spitting (drinks must be swallowed to hydrate the body) and urinating (the goal is relatively frequent, light-colored urine).
Professional golfers can spend up to eight hours a day on the golf course. Most modern players also include strength training, aerobic conditioning, and flexibility in their training schedule to strengthen the muscles involved in golf, improve endurance, and minimize the risk of injury. Golf is primarily a game of skill. Therefore, top golfers come in many shapes and sizes. In recent times, there is a tendency for top golfers to be fitter and leaner than ever before. Overweight golfers suffer greater heat intolerance in hot conditions. Carrying excess body fat may also make a golfer more susceptible to injury. Common nutrition issues include:
Training nutrition. Intake should include primarily carbohydrates with moderate amounts of protein and less fat. A variety of foods from each food group is recommended.
Tournaments. Players will usually miss a meal while playing a round. They may be faced with no carbohydrate intake for five or six hours. Players should carry fruit or cereal bars to maintain their energy levels during tournament play.
Sweat losses. Sweat loss is high when tournaments are played in hot and windy environments. It is important for players to carry water with them. Although many golf courses provide drink stations, they may be at infrequent intervals, and not allow sufficient opportunity for fluid replacement during a game.
Alcohol intake. If alcohol is used, players should consume a few nonalcohol drinks first and alternate these with one or two alcoholic drinks thereafter. Both dehydration and low blood-sugar levels are possible during competition, and may impair golfing performance.
Elite gymnasts train in excess of 20 to 30 hours per week. Typically, daily training sessions are scheduled morning and afternoon lasting for 2 to 3 hours each. An exercise can last for as little as a few seconds (vault) to over one minute (floor exercise). Technical skill perfection, muscular strength, explosive power relative to body weight, flexibility, and artistic impression are all essential characteristics required for world-class performance. Female gymnasts are small, lean (low percent body fat), and well-muscled, which results in a high power-to-weight ratio. Generally, female gymnasts reach their peak power-to-weight ratio before puberty, and are ready for elite international competition at the minimum age requirement. Male gymnasts are lean and heavily muscled, yet possess adequate flexibility and agility to perform the required skills at elite international competition. Successful male gymnasts have a high power-to-weight ratio, which is normally reached during their twenties, making them somewhat older than elite female gymnasts. Common nutrition issues include:
Calcium deficiency. Female gymnasts should consume calcium-rich foods at meals and snacks to meet their daily calcium needs for bone mineral development. These foods include low-fat or fat-free dairy products, leafy green vegetables, corn tortillas, and canned salmon.
Eating disorders. Female gymnastics is a sport where athletes are required to maintain a low weight-to-height ratio if they wish to perform at a high level. This fact places these athletes at greater risk of developing an eating disorder than athletes involved in other sports. It is important to have a weight management plan involving the doctor, the sports dietitian, the coach and the gymnast to ensure that athletes develop normally during their adolescent years.
Fluid intake. Sweat losses tend to be small compared with those of other athletes. However, it is still important for gymnasts to stop regularly during their long training sessions to replace lost fluid. Some gymnasts concerned with their weight reduce their fluid intake to reduce body weight. For these athletes, it is crucial to point out that a decrease in weight as a result of sweating is purely a reflection of lost fluid, not a decrease in body fat stores.
Energy needs. Female gymnasts often consume low calorie diets, placing them at risk for calcium and iron deficiency. Adolescent male gymnasts may have difficulty consuming enough food to keep pace with the demands of growth, training, and maintenance of muscle mass.
Serious commitment to training is needed, with 6 to 12 sessions per week and as many as 6 hours daily. Swimmers may also perform land-based aerobic training as well as weight training sessions. Pronounced upper body muscle development and low body fat is the norm, although some fat in the right distribution may enhance floatation. Many top swimmers are teenagers. Males are typically in a period of heavy growth and muscular development, requiring high energy support. Females undergoing hormonal changes which promote increased body fat may struggle to maintain low body fat levels. Common nutrition issues include:
Daily recovery. A high-energy, high-carbohydrate diet is recommended. Swimmers who travel long distances to train may need to pack nutritional snacks to begin the refueling process rather than waiting until they get home. Fatigue, loss of body weight and poor performance can result without a good plan that includes several snacks during the day which make good use of high energy foods.
Iron status. Female swimmers are especially at risk, so iron levels should be checked regularly when in heavy training. Iron-rich foods should be consumed daily.
Unwanted fat gain. Fat gain can be avoided during the off-season by decreasing total energy intake.
Fluid needs in training. Sweat losses are not always obvious because the athlete is wet. Swimmers should keep drinks on the pool deck and drink during rest periods or between sets.
A combination of three exercises, triathalon includes swimming, cycling, and running. These events are completed over various distances ranging from one hour events to all-day races. Most triathletes train twice daily and routinely combine disciplines into one session to adapt their bodies to the stresses of competition. Professionals may train three times daily. Triathletes commonly strive to achieve a low body-fat level, and this fascination with weight loss leads some to try fad diets. Common nutrition issues include:
Daily recovery. High daily energy, carbohydrate and protein requirements exist.
Timing of meals around training sessions. Planning is crucial.
Carbohydrate loading. This practice is popular before competition and can positively affect performance.
Prerace eating. Early start times make skipping breakfast tempting for some.
Eating during training and competition. Planning nutritious snacks is essential to provide carbohydrate to working muscles and to meet daily energy needs and nutrition requirements. Athletes are encouraged to use the cycling portion to consume much-needed fluids and fuel.
Meeting fluid needs. With high sweat losses, a conscious effort is needed to prevent dehydration (the most common cause of medical treatment following triathalons).
Weight management. High-protein, low-carbohydrate diets used for weight loss are not recommended because they are low in calories. Risks include failure to recover from training, and compromising immune system function.
Iron. Damage to red blood cells from the pounding of feet on the track, iron losses in sweat, gastrointestinal bleeding which may occur through heavy training or anti-inflammatory use, low dietary intake of well-absorbed iron, and menstrual losses in females can lead to iron deficiency.
Regardless of the specific sport, medical nutrition therapy or nutrition counseling can be described as the "care" of staying metabolically healthy during a run, during seasonal practice and competition, or as a year-round philosophy to perform maximally and to avoid or recover from injury. Supplementation and additives are ancillary subjects and can be positive or negative for the user. We have described several issues commonly encountered by physicians and dietitians to illustrate the varied and dynamic nature of sports nutrition.
Table. Foods, nutrients, and body function Average number of grams per serving (a) Bread, cereal, Meat, Fish, Calories rice, pasta, Poultry, per starchy Eggs, gram vegetable Fruit Vegetable Cheese Carbohydrate 4 15g 15g 5g 0g Protein 4 2g 0g 3g 21g Fat 9 1g 0g 0g 15g Alcohol 7 Water (b) 0 Average number of grams per serving (a) Added fats (butter, oils, mayonnaise) Role in body function Carbohydrate 0g The major source of fuel, essential for brain function. The body will convert fat and/or protein to glucose in the absence of carbohydrate intake (gluconeogenesis). Carbohydrate is stored in the skeletal muscle and liver in the form of glycogen. Protein 0g Source of essential amino acids necessary for the body to synthesize its own proteins and nitrogen-containing molecules. Proteins also provide life-sustaining enzymes, immunoproteins, or antibodies and peptide hormones that control many body functions. Their structural role includes both the contractile proteins of the muscles and the fibrous proteins in connective tissue, skin, nails, and hair. Fat 5g Source of essential fat-soluble vitamins and fatty acids, corticosteroid hormones, and mediators of electron transport and an important dietary energy source. Alcohol Source of calories only--no nutritional value. Water (b) Approximately 60% of the total body mass in a normal adult. Provides a medium for the solubilization and passage of nutrients. Also serves as the medium in which intracellular metabolic reactions take place. (a) Serving sizes based on USDA Dietary Guidelines for Americans. (b) Water content in foods varies greatly. Many foods, especially fruits and vegetables, can be good sources of fluid.
Accepted May 21, 2004.
1. Heimburger and Weinsier. Handbook of Clinical Nutrition. St. Louis, Mosby-Year Book, 1997.
2. Hunt and Groff. Advanced Nutrition and Human Metabolism St. Paul, West Publishing Company, 1990.
3. Louise Burke. Survival For the Fittest. Sydney, Murdoch Magazines, 2001.
4. Louise Burke. The Complete Guide to Food for Sports Performance: A Guide to Peak Nutrition for Your Sport. Sydney, Allen & Unwin, 1995.
5. Mahan and Escott-Stump. Krause's Food, Nutrition, and Diet Therapy. Philadelphia, W.B. Saunders Company, 2000.
6. Manore and Thompson. Sport Nutrition for Health and Performance. Champaign, Human Kinetics, 2000.
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1. Australian Institute of Sport (http://www.ais.org.au). Includes resources, research, hot topics, and supplements links. Nutrition issues for many specific sports are discussed.
2. Sports, Cardiovascular and Wellness Nutritionists (SCAN) (http://www.nutrifit.org). SCAN is a practice group of the American Dietetic Association.
3. The Gatorade Sports Science Institute (http://www.gssiweb.com). Although there are some commercial aspects to this site, the Sports Science Center link presents excellent scientific and sport-specific information.
4. University of Illinois Extension--Sports and Nutrition, the Winning Connection (http://www.urbanext.uiuc.edu/hsnut). Includes a pre-game meal planner.
Tracy R. Ray, MD, Rachel Fowler, MS, RD
From the American Sports Medicine Institute and the Alabama Sports Medicine and Orthopaedic Center, Birmingham, AL.
Reprint requests to Tracy R. Ray, MD, Alabama Sports Medicine and Orthopaedic Center, 1201 11th Avenue South, Suite 200, Birmingham, AL 35205. Email: email@example.com
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|Title Annotation:||Featured CME Topic: Sports Medicine|
|Publication:||Southern Medical Journal|
|Date:||Sep 1, 2004|
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