Nutrition for Athletics Presented by Janice Hermann, PhD, RD/LD OCES Adult and Older Adult Nutrition Specialist Nutrition for Athletics Being physically active has many health benefits, and good nutrition plays an important role in athletic performance. While the USDA MyPyramid provides the foundation for a healthy diet, there are some special dietary considerations for athletics. Nutrition for Athletics Nutrition can affect body weight, body composition and athletic performance. As interest in nutrition for athletic performance has increased so have promotions for ergogenic aids, supplements and herbal products claiming to improve athletic performance. Calories Meeting calorie needs is a priority for athletic performance. Inadequate calories can hinder athletic training and performance. Inadequate calories can result in loss of muscle as well as body fat. Muscle loss can result in loss of strength and endurance. In addition, inadequate calories can result in poor nutrient intake. Calories Calorie needs are affected by an individual’s age, gender, body size, muscle mass, as well as the frequency, intensity and duration of physical activity. One way to determine if adequate calories are consumed is if body weight and composition are maintained. Weight Change Athletes often want to increase or decrease their body weight to meet sports demands. Weight change should occur slowly during the off-season, or beginning of the beginning before composition begins. Weight Change Weight gain can be accomplished by an increase in calorie intake by 500 to 1,000 calories per day in combination with an increase in strength training which can result in an increase in muscle mass. Weight Change Weight loss can be accomplished by decreasing calorie intake by 500 calories per day while maintaining a healthy diet. Weight loss should be gradual, approximately 1-2 pounds/week. Slow weight loss contributes to a loss in body fat while maintaining muscle. Rapid weight loss increases the risk of losing muscle and regaining weight. Weight Change The best combination for weight loss is a regular fitness program along with a well- balanced, low-fat diet following the USDA MyPyramid. Weight Change Weight loss may seem small at first when using a combination of diet and increased physical activity, because muscle mass increases at the same time body fat decreases. However, greater weight loss becomes apparent as body fat loss continues and muscle gain levels off. Weight Change Weight loss techniques involving loss of body water are dangerous. Water loss results in decreased blood volume and reduced blood flow to the kidneys, skin, and muscles. This hinders the body’s ability to sweat and regulate body temperature, and increases the risk of dehydration. Weight Change Determining a healthy body weight is critical. A healthy weight is one that can be realistically maintained, allows for positive increases in athletic performance and minimizes risk of injury. Weight Change Pressure to achieve unrealistic body weights can lead to chronic dieting and eating disorders in severe cases. In addition, pressure to loss weight can encourage athletes to follow unhealthy weight loss methods. Weight Change Excessive weight loss can especially be a problem for female athletes. In females, low calorie intakes in combination with high energy expenditures can lead to amenorrhea and loss of or failure to gain bone mass. Body Composition Body weight and composition are two major factors that affect athletic performance. Body weight can affect speed, endurance, and power; whereas body composition can influence strength, agility and appearance. Body Composition Most athletes need a high strength-to-weight ratio to enhance athletic performance. Because body fat adds to weight without adding strength, a low percentage of body fat is often emphasized; however, too little body fat can also hinder performance and health. Body Composition Optimal body weight and composition differs based on an age, gender, genetics, and type of athletic event. Yet some athletic events set weight criteria that may not be optimal for an individual athlete – such as wrestling which may require athletes to lose or gain weight for specific weight categories. Body Composition Other athletic events such as dance and gymnastics may pressure athletes to lose weight and have low body fat to have a lean physique that may not be ideal. Extreme calorie restrictions can result in a decreased in both body fat and muscle which can hinder athletic performance. Body Composition Optimal body fat percentages vary depending on gender and the type of athletic event. Athletes who try achieve unrealistic inappropriate body weight or body fat levels may be at risk for eating disorders or other health problems related to inadequate calories or nutrients. Macronutrients There isn’t evidence that athletes need a diet significantly different from that recommended in the Acceptable Macronutrient Distribution Ranges: 45-65% carbohydrate 10-35% protein 20-35% fat Protein Protein needs for athletes have received a lot of investigation, not only in terms of whether protein needs are increased, but also in terms of whether individual amino acids are beneficial. Athletes do have slightly higher protein requirements to support increased muscle mass and muscle repair. Protein The amount of increase depends on the type of athletic activity, intensity, duration, and possibly the gender. Protein requirement may vary from 1.2 g/kg for endurance athletes to 1.7 g/kg for bodybuilders and strength athletes. General adult RDA for protein 0.8 g/kg Increased protein beyond recommended levels is unlikely to result in additional increases in muscle mass. Protein It is important to realize that if calorie intake is not adequate, protein will be used for energy. It is also important to realize that most typical diets provide enough protein to cover even the increased protein needs of athletes. Protein The effect of using individual amino acids to improve athletic performance has been inconsistent. Because the safety and efficacy of individual amino acid mixtures has not been established, their use cannot be recommended. Vitamins and Minerals Vitamins and minerals have important roles in athletic performance for energy production, hemoglobin synthesis, bone health, immune function, and protecting body tissues from oxidative damage. Vitamins and minerals are also required to help build and repair muscle. Vitamins and Minerals Although theoretically, physical activity may increase or alter vitamin and mineral requirements; it is assumed that the current Dietary Reference Intakes (DRIs) are appropriate for athletes unless otherwise stated. Vitamins and Minerals Athletes at risk for poor vitamin and mineral intakes are those who severely limit calories, eliminate one or more of the food groups from their diet, or consume high- carbohydrate, low nutrient dense diets. Vitamins and Minerals Athletes participating in the previous types of behaviors may need to use a multivitamin/mineral supplement to improve their overall nutritional status. Supplementing single vitamins and minerals is discourages unless there is a clear medical or nutritional reasons; such as an iron supplement for iron deficiency anemia. Vitamins and Minerals The B-complex vitamins; thiamin, riboflavin, niacin, vitamin B-6, pantothenic acid and biotin are involved in energy production and folate and vitamin B-12 are needed for the production or red blood cells, protein synthesis and tissue maintenance and repair. Vitamins and Minerals There is limited research available to determine if athletes need more B-complex vitamins; however, the some research suggests athlete may have a slightly higher need for these vitamins, perhaps up to twice the recommended amount. However, these increased needs can generally be met by athletes higher calorie needs to maintain body weight. Antioxidant Nutrients Antioxidant nutrients such as vitamins A, E, and C, beta-carotene, and selenium have important roles in protecting cell membranes from oxidative damage. Because physical activity increases oxygen use it has been hypothesized that intense physical activity produces “oxidative stress.” Antioxidant Nutrients Thus, at this time there is no clear consensus on whether athletes need additional antioxidant nutrients. Athletes at greatest risk for poor antioxidant status are those who limit calories, consume a low-fat diet, or limit fruit and vegetable intake. Minerals Minerals typically low in athletes diets, especially for females, include calcium, iron and zinc. Low intake of these minerals is usually due to low calorie intake or limiting animal products such as meat, fish, poultry, and dairy products. Calcium Calcium is important for building and repairing bone and maintaining blood calcium levels. Inadequate calcium intake increases the risk of low bone mineral density and stress fractures. Female athletes are at greatest risk for low bone mineral density if calorie intake is low, dairy products are omitted from the diet, and amenorrhea is present. Vitamin D Vitamin D is needed for calcium absorption, regulation of blood calcium levels, and bone health. Two main sources of vitamin D are fortified foods, such as milk, and production of vitamin D by sunlight exposure on the skin. Vitamin D Athletes living in northern regions, who train and compete indoors throughout the year such as gymnasts and figure skaters are at greater risk for poor vitamin D status if they do not consume foods fortified with vitamin D. These athletes may benefit from vitamin D supplementation at the recommended DRI level. Iron Iron has an important role in the formation of hemoglobin and myoglobin, which carry oxygen in the body, and for enzymes involved in energy production. Iron depletion is a common nutrient problem among athletes, especially females. Iron If iron depletion progresses to iron deficiency anemia, athletic performance can be hindered. Iron depletion is usually due to low calorie intake, limiting meat, fish and poultry that contain iron in the readily available heme form, vegetarian diets that contain foods with low iron bioavailability, or increased iron losses. Iron Female athletes and long-distance runners should be periodically screened to evaluate their iron status. Because iron deficiency anemia can take three to six months to reverse early nutritional intervention is beneficial. Iron Some athletes may develop a transient decrease in hemoglobin when they begin training as a result of the increase in blood volume which dilutes hemoglobin. This situation doesn’t appear to hinder athletic performance. Zinc Most dietary zinc comes from animal foods and a majority of people consume less than DRI amounts recommended. Because zinc has important roles in growth, building and repairing muscle tissue, and energy production, it is prudent to evaluate zinc status, especially among female athletes. Fluids It is well known that dehydrate can hinder athletic performance. In addition, dehydration can increase the risk of heat stroke which is potentially life- threatening. Thus athletes need to keep well-hydrated before and during physical activity. Fluids One way the body cools itself by vaporizing water. Sweat rates vary depending of body size, exercise intensity, temperature, humidity and acclimation but can exceed 1,800 mL/hour. In addition, to water, sweat contains substantial amounts of sodium and modest amounts of potassium. Fluids Fluid balance is maintained if fluid intake and absorption equals fluid loss through sweating, and in longer events – urination. Fluid balance during physical activity is not always possible because maximum sweat rates exceed maximum stomach emptying, which limits fluid absorption. Fluids However, usually athlete’s fluid intake during physical activity is less that the amount that can be emptied from the stomach and absorbed. Athletes often consume less than 500 mL/hour during competition and the stomach emptying rate is more than 1 L/hour. Fluids Stomach emptying is increased when the amount of fluid in the stomach is high. Stomach emptying is decreased with concentrated fluids, carbohydrate concentration is greater than or equal to 8%. Fluids Dehydration, hypohydration, and hyponatremia are all distortions in fluid and electrolyte balance that can be life- threatening. Dehydration can occur when fluid losses exceed fluid intakes. Hypohydration can occur when athletes dehydrate themselves before beginning an event – such as to make a weight category. Fluids Hyponatremia (low blood sodium concentrations) can occur due to prolonged, heavy sweating without replacing sodium, or when excess water is retained in the body. Although endurance athletes are more likely to suffer from dehydration than from hyponatremia (overhydration), hyponatremia is not uncommon. Fluid and Electrolyte Recommendations Before Activity: Athletes should be well- hydrated before physical activity. Recommendations are to drink generous amounts of fluid 24 hours before an event, and 400 to 600 mL of fluid 2-3 hours before an event (1.5-2.5 cups). This amount should maximize hydration while still allowing enough time for excess fluid to be excreted in the urine. Fluid and Electrolyte Recommendations During Activity: During an event athletes should try to drink enough fluid to maintain fluid balance. Even partial dehydration can hinder athletic performance. Fluid and Electrolyte Recommendations During Activity: If fluid balance cannot be maintained, the maximal amount of fluid that can be tolerated should be consumed. Athletes can optimize hydration by drinking 150 to 350 mL of fluid (approximately 6-12 oz) every 15 to 20 minutes during the event. Fluid and Electrolyte Recommendations Beverages contain carbohydrate at concentrations of 4-8% are recommended for events lasting longer than one hour. These type of beverages are also acceptable for hydration during events lasting less than one hour although plain water is also appropriate under these conditions. Fluid and Electrolyte Recommendations Little need to replace electrolytes for events, less than 3 to 4 hours, especially if pervious meal contained sodium. However, consuming beverages containing modest amounts of sodium is recommended during events lasting longer than one hour because it may increase acceptability and desire to drink, thus increasing the amount of fluid consumed. Fluid and Electrolyte Recommendations Consuming beverages containing sodium may also help prevent hyponatremia in susceptible people. Although most athletes who consume more fluid than they lose in sweat excrete the excess fluid as urine, some people retained fluid. Fluid and Electrolyte Recommendations Beverages containing sodium could help prevent dilution of blood sodium levels, thus decreasing the risk of hyponatremia. Limiting fluid intake so that it does not exceed losses from sweat can also decrease the risk of hyponatremia. Fluid and Electrolyte Recommendations After Activity: Usually athletes do not consume enough fluids during activity to balance fluid losses. As a result most athletes are dehydrated to some extent at the end of athletic events. Consuming up to 150% of weight lost during an activity may be needed to replace losses in sweat and urine. Including sodium in fluids reduces diuresis that occurs with plain water. Fluid and Electrolyte Recommendations After Activity: Sodium also helps the body rehydrate by maintaining blood osmolality and thus the desire to drink. Because most commercial beverages do not contain enough sodium to maximize post activity fluid replacement, sodium containing beverages should be consumed in combination with a sodium containing meal. Weather Conditions Hot and humid weather: The risk of dehydration and heat related injury increases dramatically in hot and humid weather. If outside temperature exceeds body temperature, heat cannot be released by radiation. If humidity is high, the ability to remove heat by sweat evaporation decreases. Weather Conditions Hot and humid weather: If both temperature and humidity are high, there is a very high risk of heat related illness and athletic events should be delayed. If athletic activities do occur under these conditions, precaution should be taken to be sure that athletes consume plenty of fluids and are monitored for heat related illness. Weather Conditions Cold weather: Although the risk of dehydration is greater in hot weather, dehydration is not uncommon in cold weather. Factors can contribute to dehydration in cold temperatures include respiratory fluid losses in cold dry temperatures, as well as sweat losses that may be high if insulated clothing is worn during intense athletic events. Weather Conditions Cold weather: Dehydration can also occur due to low fluid intake. Low fluid intakes can occur if an athlete is cold and available fluids are cold, which can reduce the athlete’s desire to drink. In addition, difficulty removing multiple layers of clothing to urinate may cause some athletes to voluntarily limit fluid intake. Weather Conditions Altitude: Altitudes higher than 8,200 feet may result in fluid losses beyond those due to physical activity. These losses occur due to mandatory diuresis, high respiratory water losses, and decreased appetite. Weather Conditions Altitude: Under circumstances of weight maintenance, diuresis in about 500 mL/day and lasts for about 7 days. Respiratory water losses may be as high as 1,900 mL/day in men and 850 mL/day in women. Thus, fluid intake should be increased at high altitude to as much as 3 to 4 L per day to assure optimal kidney function. Training Diet Portion of calories from protein, fat, and carbohydrate for athlete’s training diets don’t differ substantively from current recommendations for the general population. Thus athlete’s training diet should follow the guidelines recommended by the Dietary Guidelines for Americans and the USDA MyPyramid. Training Diet The main differences between an athlete’s diet and that of the general population are that athletes need additional fluid to cover sweat losses and calories to for the physical activity itself. Much of additional calorie needs should be supplied by carbohydrate. Training Diet Although in some cases the need for other nutrients may also increase (protein, B- complex vitamins), the increase in calorie needs appear to exceed the increased need for other nutrients. As a result, as calorie needs increase, athletes should first try to consume the recommended amount of foods from the MyPyramid food groups. Training Diet Another issue for athletes is the timing of meals and snacks. For the most part foods and fluids consumed around athletic activities need to be determined on an individual basis and will partly depend on an athlete’s gastrointestinal characteristics and activity intensity. Training Diet An individual may be able to handle a snack of milk and a sandwich one hour before a light activity, but would be uncomfortable if the same snack was consumed before a very hard activity. Athletes in heavy training or participating in multiple daily workouts may need to eat more than 3 meals and 3 snacks per day. Pre Activity Meal Eating before physical activity has been shown to improve athletic performance versus being in a fasting state. A meal or snack before and event or an intense workout should prepare the athlete for the event, not leave them hungry or with undigested food in their stomach. Pre Activity Meal Recommendations for meals and snacks before events are that they should provide enough fluid to maintain hydration, be low in fat and fiber to help gastric emptying and lower gastrointestinal distress, be high in carbohydrate to maintain blood glucose and maximize glycogen stores, be moderate in protein, and contain foods the athlete is familiar with. Pre Activity Meal The size and timing of pre-competition meals are interrelated. Because most athletes do not like to compete on a full stomach, smaller meals should be consumed closer to the time of the event to allow for gastric emptying, whereas larger meals can be consumed if adequate time is available before competition. Pre Activity Meal The amount of carbohydrate consumed in studies in which athletic performance is enhance range from approximately 200 to 300 g carbohydrate for meals consumed 3 to 4 hours before the competition. Pre Activity Meal Recommendations on the amount of carbohydrate consumed within one hour before an event is controversial. Early research suggested this could lead to hypoglycemia and premature fatigue; however, more recent studies have reported either no effect or beneficial effects of pre- event carbohydrate intake on performance. Pre Activity Meal The form of pre-competition meals and snacks depends on athlete’s individual tolerances. Some athletes can handle regular meals 2 to 4 hours before exercise; however, this may cause severe gastrointestinal distress for others and they may do better with liquid meals. During Activity Consuming carbohydrate in amounts typically supplied in sports drinks (4-8%) improves performance in events lasting one hour or less has been controversial. Current research now supports the benefit of this practice, especially in athletes who are physically active in the morning after an overnight fast when liver glycogen levels are low. During Activity For longer events, consuming 0.7 g carbohydrate/kg body weight per hour (approximately 30 to 60 g carbohydrate per hour) has been shown to extend endurance performance. Consuming carbohydrate during physical activity is even more important for athletes who have not carbohydrate-loaded, consumed a pre-event meal, or restrict calorie intake for weight loss. During Activity Carbohydrate intake should begin shortly after the onset of physical activity. Research has shown that consuming a larger amount of carbohydrate after 2 hours of physical activity is not as effective as consuming the same amount of carbohydrate in 15 to 20 minute intervals during the first 2 hours of physical activity. During Activity The type of carbohydrate should provide primarily glucose; fructose alone is not as effective and may lead to diarrhea, although mixtures of glucose and fructose seem to be effective. The form of carbohydrate, solid food or liquid doesn’t seem to matter and is more a matter of personal preference. Post Activity Meal Timing and composition of the post activity meal or snack depends on the length and intensity of the physical activity (whether glycogen stores are depleted) and when the next intense physical activity will occur. Post Activity Meal After a marathon most athletes will have depleted glycogen stores; whereas after a 60 minute training session, glycogen stores may not be depleted. However, most athletes after completing a marathon won’t be competing in another marathon the next day. Post Activity Meal As a result, the timing and composition of post activity meals for these athletes is less important because they have time to restore glycogen store. However, post event recovery is very important for athletes who participate in multiple events in one day or have a short recovery time between events. Post Activity Meal Timing of post activity carbohydrate affects glycogen stores. Carbohydrate consumed immediately after physical activity (1.5 g carbohydrate/kg at 2 hour intervals) results in higher glycogen stores than if carbohydrate intake is delaying for 2 hours. Timing of post activity carbohydrate is not as critical for athletes who have one or more days between intense events. Post Activity Meal If adequate carbohydrate is consumed over a 24 hour period, the timing of carbohydrate intake does not appear to affect the amount of glycogen stored. However, consuming a meal or snack close to the end of physical activity may be important for athletes to meet their carbohydrate and calorie needs. Post Activity Meal The type of carbohydrate consumed can also affect post exercise glycogen stores. In regards to simple sugars, glucose and sucrose are equally affective if consumed at a rate of 1.5 g/kg body weight for 2 hours; however, fructose alone is less effective. Post Activity Meal In regards to whole foods, consuming foods with a high glycemic index produces higher muscle glycogen stores 24 hours after activity as compared to the same amount of carbohydrate from foods with a lower glycemic index. However, the usefulness of these findings must be considered in terms of the overall diet. Post Activity Meal When similar amounts of carbohydrates or carbohydrates, protein and fat are provided following activity, glycogen synthesis is similar. Although including protein doesn’t appear to enhance glycogen stores, including protein in a post activity meal may provide needed amino acids for muscle protein repair. Ergogenic Aids Marketing of ergogenic aids (items claiming to increase athletic performance) preys on athletes. The 1994 Dietary Supplement Health and Education Act allows supplement manufactures to make claims regarding the effect of products on the structure/function of the body. Ergogenic Aids Ergogenic aids must be carefully evaluated in terns of the validity of the claim relative to the science of nutrition, athletic performance and health consequences. Ergogenic Aids In general, most ergogenic aids fall into one of the following categories: those that perform as claimed those that may perform as claimed but for which there is insufficient evidence of efficacy at this time those that do not perform as claimed those which are dangerous, banned, or illegal, and should not be used. Ergogenic Aids Use of ergogenic aids is controversial. Some health care professionals discourage use of all ergogenic aids whereas others suggest they be used with caution but only after athletes have carefully evaluated of the product for safety, efficacy, potency and legality and discussed the use of the product with a qualified nutrition or health professional.
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