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Old 08-21-2009, 05:54 AM   #1
Darryl Shaw
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Join Date: Apr 2008
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Default Nutrition and Athletic Performance.

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Nutrition and Athletic Performance.

ABSTRACT


It is the position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine that physical activity, athletic performance, and recovery from exercise are enhanced by optimal nutrition. These organizations recommend appropriate selection of foods and fluids, timing of intake, and supplement choices for optimal health and exercise performance. This updated position paper couples a rigorous, systematic, evidence-based analysis of nutrition and performance-specific literature with current scientific data related to energy needs, assessment of body composition, strategies for weight change, nutrient and fluid needs, special nutrient needs during training and competition, the use of supplements and ergogenic aids, nutrition recommendations for vegetarian athletes, and the roles and responsibilities of the sports dietitian. Energy and macronutrient needs, especially carbohydrate and protein, must be met during times of high physical activity to maintain body weight, replenish glycogen stores, and provide adequate protein to build and repair tissue. Fat intake should be sufficient to provide the essential fatty acids and fat-soluble vitamins and to contribute energy for weight maintenance. Although exercise performance can be affected by body weight and composition, these physical measures should not be a criterion for sports performance and daily weigh-ins are discouraged. Adequate food and fluid should be consumed before, during, and after exercise to help maintain blood glucose concentration during exercise, maximize exercise performance, and improve recovery time. Athletes should be well hydrated before exercise and drink enough fluid during and after exercise to balance fluid losses. Sports beverages containing carbohydrates and electrolytes may be consumed before, during, and after exercise to help maintain blood glucose concentration, provide fuel for muscles, and decrease risk of dehydration and hyponatremia. Vitamin and mineral supplements are not needed if adequate energy to maintain body weight is consumed from a variety of foods. However, athletes who restrict energy intake, use severe weight-loss practices, eliminate one or more food groups from their diet, or consume unbalanced diets with low micronutrient density may require supplements. Because regulations specific to nutritional ergogenic aids are poorly enforced, they should be used with caution and only after careful product evaluation for safety, efficacy, potency, and legality. A qualified sports dietitian and, in particular, the Board Certified Specialist in Sports Dietetics in the United States, should provide individualized nutrition direction and advice after a comprehensive nutrition assessment.

KEY POINTS

The following key points summarize the current energy, nutrient, and fluid recommendations for active adults and competitive athletes. These general recommendations can be adjusted by sports nutrition experts to accommodate the unique concerns of individual athletes regarding health, sports, nutrient needs, food preferences, and body weight and body composition goals.

* Athletes need to consume adequate energy during periods of high-intensity and/or long-duration training to maintain body weight and health and maximize training effects. Low energy intakes can result in loss of muscle mass; menstrual dysfunction; loss of or failure to gain bone density; an increased risk of fatigue, injury, and illness; and a prolonged recovery process.

* Body weight and composition should not be used as the sole criterion for participation in sports; daily weigh-ins are discouraged. Optimal body fat levels depend on the sex, age, and heredity of the athlete and may be sport-specific. Body fat assessment techniques have inherent variability and limitations. Preferably, weight loss (fat loss) should take place during the off-season or begin before the competitive season and involve a qualified sports dietitian.

* Carbohydrate recommendations for athletes range from 6 to 10 g·kg-1 body weight·d-1 (2.7-4.5 g·lb-1 body weight·d-1). Carbohydrates maintain blood glucose levels during exercise and replace muscle glycogen. The amount required depends on the athlete's total daily energy expenditure, type of sport, sex, and environmental conditions.

* Protein recommendations for endurance and strength-trained athletes range from 1.2 to 1.7 g·kg-1 body weight·d-1 (0.5-0.8 g·lb-1 body weight·d-1). These recommended protein intakes can generally be met through diet alone, without the use of protein or amino acid supplements. Energy intake sufficient to maintain body weight is necessary for optimal protein use and performance.

* Fat intake should range from 20% to 35% of total energy intake. Consuming ≤20% of energy from fat does not benefit performance. Fat, which is a source of energy, fat-soluble vitamins, and essential fatty acids, is important in the diets of athletes. High-fat diets are not recommended for athletes.

* Athletes who restrict energy intake or use severe weight-loss practices, eliminate one or more food groups from their diet, or consume high- or low-carbohydrate diets of low micronutrient density are at greatest risk of micronutrient deficiencies. Athletes should consume diets that provide at least the recommended dietary allowance (RDA) for all micronutrients.

* Dehydration (water deficit in excess of 2-3% body mass) decreases exercise performance; thus, adequate fluid intake before, during, and after exercise is important for health and optimal performance. The goal of drinking is to prevent dehydration from occurring during exercise and individuals should not drink in excess of sweating rate. After exercise, approximately 16-24 oz (450-675 mL) of fluid for every pound (0.5 kg) of body weight lost during exercise.

* Before exercise, a meal or snack should provide sufficient fluid to maintain hydration, be relatively low in fat and fiber to facilitate gastric emptying and minimize gastrointestinal distress, be relatively high in carbohydrate to maximize maintenance of blood glucose, be moderate in protein, be composed of familiar foods, and be well tolerated by the athlete.

* During exercise, primary goals for nutrient consumption are to replace fluid losses and provide carbohydrates (approximately 30-60 g·h-1) for maintenance of blood glucose levels. These nutrition guidelines are especially important for endurance events lasting longer than an hour when the athlete has not consumed adequate food or fluid before exercise or when the athlete is exercising in an extreme environment (heat, cold, or high altitude).

* After exercise, dietary goals are to provide adequate fluids, electrolytes, energy, and carbohydrates to replace muscle glycogen and ensure rapid recovery. A carbohydrate intake of approximately 1.0-1.5 g·kg-1 body weight (0.5-0.7 g·lb-1) during the first 30 min and again every 2 h for 4-6 h will be adequate to replace glycogen stores. Protein consumed after exercise will provide amino acids for building and repair of muscle tissue.

* In general, no vitamin and mineral supplements are required if an athlete is consuming adequate energy from a variety of foods to maintain body weight. Supplementation recommendations unrelated to exercise, such as folic acid for women of childbearing potential, should be followed. A multivitamin/mineral supplement may be appropriate if an athlete is dieting, habitually eliminating foods or food groups, is ill or recovering from injury, or has a specific micronutrient deficiency. Single-nutrient supplements may be appropriate for a specific medical or nutritional reason (e.g., iron supplements to correct iron deficiency anemia).

* Athletes should be counseled regarding the appropriate use of ergogenic aids. Such products should only be used after careful evaluation for safety, efficacy, potency, and legality.

* Vegetarian athletes may be at risk for low intakes of energy, protein, fat, and key micronutrients such as iron, calcium, vitamin D, riboflavin, zinc, and vitamin B12. Consultation with a sports dietitian is recommended to avoid these nutrition problems.
http://journals.lww.com/acsm-msse/Fu...rmance.27.aspx

http://www.eatright.org/WorkArea/lin...id&ItemID=8435 (pdf)

See also:

IOC Sportsoracle.com - Nutrition for Athletes.

IAAF.org - Nutrition for Athletics.

Eatright.org - Sports Nutrition.
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