from the association
           Position of the American Dietetic Association,
      Dietitians of Canada, and the America...
plement choices for optimal health                 does not benefit performance. Fat,              weight during the first 3...
mary fuel used for high intensity, short
    Topic                        Question                                        ...
not alter the total amount of energy
expended but rather the proportion of       Adult man
energy derived from carbohydrat...
vantageous in sports where speed is        ter weighing, dual-energy x-ray ab-          Kinanthropometry techniques (26) a...
Setting and monitoring goals
 ● Set realistic weight and body composition goals. Ask the athlete:
       What is the maxim...
Intakes for protein and amino acids         supplementation with individual           pathways where micronutrients are
(48); however, these increased needs      dant supplements enhance physical           quate dietary calcium and vitamin D
are more prevalent in female ath-          difficult to measure because clear as-        adequate for maintaining normal po...
ter, sweat also contains substantial but   Although some individuals begin ex-      lytes lost during exercise. Rapid and
THE TRAINING DIET                          fore competition results in improved        whether the glycemic index of carbo...
ercise is even more important in situ-      will finish a marathon with depleted        repair and promote a more anabolic
Revisión nutricion y rendimiento
Revisión nutricion y rendimiento
Revisión nutricion y rendimiento
Revisión nutricion y rendimiento
Revisión nutricion y rendimiento
Revisión nutricion y rendimiento
Revisión nutricion y rendimiento
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Revisión nutricion y rendimiento


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Revisión nutricion y rendimiento

  1. 1. from the association Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance ABSTRACT This American Dietetic Association (ADA) position paper uses ADA’s It is the position of the American Die- Evidence Analysis Process and information from ADA’s Evidence Analysis tetic Association, Dietitians of Canada, Library. Similar information is also available from Dietitians of Canada’s and the American College of Sports Practice-based Evidence in Nutrition. The use of an evidence-based ap- Medicine that physical activity, ath- proach provides important added benefits to earlier review methods. The letic performance, and recovery from major advantage of the approach is the more rigorous standardization of exercise are enhanced by optimal review criteria, which minimizes the likelihood of reviewer bias and in- nutrition. These organizations rec- creases the ease with which disparate articles may be compared. For a ommend appropriate selection of detailed description of the methods used in the evidence analysis process, foods and fluids, timing of intake, access ADA’s Evidence Analysis Process at and supplement choices for optimal Conclusion Statements are assigned a grade by an expert work group health and exercise performance. based on the systematic analysis and evaluation of the supporting research This updated position paper couples evidence. Grade I Good, Grade II Fair, Grade III Limited, Grade IV a rigorous, systematic, evidence- Expert Opinion Only, and Grade V Grade Is Not Assignable (because there based analysis of nutrition and is no evidence to support or refute the conclusion). performance-specific literature with Evidence-based information for this and other topics can be found at current scientific data related to and and sub- energy needs, assessment of body scriptions for non-ADA members are available for purchase at https:// composition, strategies for weight Subscriptions for Dietitians of change, nutrient and fluid needs, Canada and non-Dietitians of Canada members are available for Practice- special nutrient needs during train- based Evidence in Nutrition at ing and competition, the use of asp. supplements and ergogenic aids, nu- trition recommendations for vege- tarian athletes, and the roles and maintain blood glucose concentra- genic aids are poorly enforced, they responsibilities of sports dietitians. tion during exercise, maximize exer- should be used with caution, and Energy and macronutrient needs, cise performance, and improve re- only after careful product evalua- especially carbohydrate and protein, covery time. Athletes should be well tion for safety, efficacy, potency, and must be met during times of high hydrated before exercise and drink legality. A qualified sports dietitian physical activity to maintain body enough fluid during and after exer- and in particular in the United weight, replenish glycogen stores, cise to balance fluid losses. Sports States, a Board Certified Specialist and provide adequate protein to beverages containing carbohydrates in Sports Dietetics, should provide build and repair tissue. Fat intake and electrolytes may be consumed individualized nutrition direction should be sufficient to provide the before, during, and after exercise to and advice subsequent to a compre- essential fatty acids and fat-soluble help maintain blood glucose concen- hensive nutrition assessment. vitamins, as well as contribute tration, provide fuel for muscles, J Am Diet Assoc. 2009;109:509-527. energy for weight maintenance. Al- and decrease risk of dehydration though exercise performance can be and hyponatremia. Vitamin and affected by body weight and compo- mineral supplements are not needed POSITION STATEMENT sition, these physical measures if adequate energy to maintain body should not be a criterion for sports weight is consumed from a variety It is the position of the American Die- performance and daily weigh-ins of foods. However, athletes who re- tetic Association, Dietitians of Can- are discouraged. Adequate food and strict energy intake, use severe ada, and the American College of fluid should be consumed before, weight-loss practices, eliminate one Sports Medicine that physical activ- during, and after exercise to help or more food groups from their diet, ity, athletic performance, and recovery or consume unbalanced diets with from exercise are enhanced by optimal low micronutrient density, may re- nutrition. These organizations recom- 0002-8223/09/10903-0017$36.00/0 quire supplements. Because regula- mend appropriate selection of food doi: 10.1016/j.jada.2009.01.005 tions specific to nutritional ergo- and fluids, timing of intake, and sup- © 2009 by the American Dietetic Association Journal of the AMERICAN DIETETIC ASSOCIATION 509
  2. 2. plement choices for optimal health does not benefit performance. Fat, weight during the first 30 minutes and exercise performance. which is a source of energy, fat-sol- and again every 2 hours for 4 to 6 uble vitamins, and essential fatty hours will be adequate to replace gly- T he following key points summa- acids, is important in the diets of cogen stores. Protein consumed after rize the current energy, nutrient, athletes. High-fat diets are not rec- exercise will provide amino acids for and fluid recommendations for ommended for athletes. building and repair of muscle tissue. active adults and competitive ath- ● Athletes who restrict energy intake ● In general, no vitamin and mineral letes. These general recommenda- or use severe weight-loss practices, supplements are required if an ath- tions can be adjusted by sports nutri- eliminate one or more food groups lete is consuming adequate energy tion experts to accommodate the from their diet, or consume high- or from a variety of foods to maintain unique concerns of individual ath- low-carbohydrate diets of low mi- body weight. Supplementation rec- letes regarding health, sports, nutri- cronutrient density are at greatest ommendations unrelated to exercise, ent needs, food preferences, and body risk of micronutrient deficiencies. such as folic acid for women of child- weight and body composition goals. Athletes should consume diets that bearing potential, should be followed. provide at least the Recommended A multivitamin/mineral supplement ● Athletes need to consume adequate Dietary Allowance (RDA) for all mi- may be appropriate if an athlete is energy during periods of high-in- cronutrients. dieting, habitually eliminating foods tensity and/or long-duration train- ● Dehydration (water deficit in excess or food groups, is ill or recovering ing to maintain body weight and of 2% to 3% body mass) decreases from injury, or has a specific micro- health and maximize training ef- exercise performance; thus, ade- nutrient deficiency. Single-nutrient fects. Low energy intakes can result quate fluid intake before, during, supplements may be appropriate for in loss of muscle mass; menstrual and after exercise is important for a specific medical or nutritional rea- dysfunction; loss of or failure to health and optimal performance. son (eg, iron supplements to correct gain bone density; an increased risk The goal of drinking is to prevent iron deficiency anemia). of fatigue, injury, and illness; and a dehydration from occurring during ● Athletes should be counseled re- prolonged recovery process. exercise and individuals should not garding the appropriate use of ergo- ● Body weight and composition should drink in excess of sweating rate. Af- genic aids. Such products should not be the sole criterion for participa- ter exercise, the athlete should only be used after careful evalua- tion in sports; daily weigh-ins are dis- drink adequate fluids to replace tion for safety, efficacy, potency, couraged. Optimal body fat levels de- sweat losses during exercise, ap- and legality. pend upon the sex, age, and heredity proximately 16 to 24 oz (450 to 675 ● Vegetarian athletes may be at risk of the athlete, and may be sport-spe- mL) fluid for every pound (0.5 kg) of for low intakes of energy, protein, cific. Body fat assessment techniques body weight lost during exercise. fat, and key micronutrients such as have inherent variability and limita- ● Before exercise, a meal or snack iron, calcium, vitamin D, riboflavin, tions. Preferably, weight loss (fat should provide sufficient fluid to zinc, and vitamin B-12. Consulta- loss) should take place during the off- maintain hydration, be relatively tion with a sports dietitian is rec- season or begin before the competi- low in fat and fiber to facilitate gas- ommended to avoid these nutrition tive season and involve a qualified tric emptying and minimize gastro- problems. sports dietitian. intestinal distress, be relatively ● Carbohydrate recommendations for high in carbohydrate to maximize athletes range from 6 to 10 g/kg (2.7 maintenance of blood glucose, be EVIDENCE-BASED ANALYSIS to 4.5 g/lb) body weight per day. moderate in protein, be composed of Studies used in the development of Carbohydrates maintain blood glu- familiar foods, and be well tolerated this position paper were identified cose levels during exercise and re- by the athlete. from the PubMed database main- place muscle glycogen. The amount ● During exercise, primary goals for tained by the National Library of required depends upon the athlete’s nutrient consumption are to replace Medicine and CENTRAL database, as total daily energy expenditure, type fluid losses and provide carbohy- well as through research articles and of sport, sex, and environmental drates (approximately 30 to 60 g per literature reviews. Five topic-specific conditions. hour) for maintenance of blood glu- questions were identified for evi- ● Protein recommendations for endur- cose levels. These nutrition guide- dence-based analysis (Figure 1) and ance and strength-trained athletes lines are especially important for en- incorporated into this position, updat- range from 1.2 to 1.7 g/kg (0.5 to 0.8 durance events lasting longer than ing the prior position on nutrition and g/lb) body weight per day. These rec- an hour when an athlete has not con- performance (1). Search terms used ommended protein intakes can gen- sumed adequate food or fluid before were athlete, performance, power, erally be met through diet alone, exercise, or if an athlete is exercising strength, endurance, or competition without the use of protein or amino in an extreme environment (eg, heat, and macronutrient, meal, carbohy- acid supplements. Energy intake suf- cold, or high altitude). drate, fat, protein, or energy. For the ficient to maintain body weight is ● After exercise, dietary goals are to purpose of this analysis, inclusion cri- necessary for optimal protein use provide adequate fluids, electrolytes, teria were adults aged 18 to 40 years; and performance. energy, and carbohydrates to replace all sport settings; and trained ath- ● Fat intake should range from 20% muscle glycogen and ensure rapid re- letes, athletes in training, or individ- to 35% of total energy intake. Con- covery. A carbohydrate intake of uals regularly exercising. Since the suming 20% of energy from fat 1.0 to 1.5 g/kg (0.5 to 0.7 g/lb) body grading system used provides allow- 510 March 2009 Volume 109 Number 3
  3. 3. mary fuel used for high intensity, short Topic Question duration activities such as the clean and jerk in weight lifting, or fast break ● Energy balance and What is the relationship between energy balance/imbalance, in basketball. body composition body composition, and/or weight management and The anaerobic glycolytic pathway athletic performance? uses muscle glycogen and glucose ● Training What is the evidence to support a particular meal timing, that are rapidly metabolized anaero- energy intake, and macronutrient intake for optimal bically through the glycolytic cascade. athletic performance during training? This pathway supports events lasting ● Competition What is the evidence to support a particular meal timing, 60 to 180 seconds. Approximately energy intake, and macronutrient intake for optimal 25% to 35% of total muscle glycogen athletic performance during competition during the 24 stores are used during a single 30- hours before competition? second sprint or resistance exercise What is the evidence to support a particular meal timing, bout. Neither the phosphagen nor the energy intake, and macronutrient intake for optimal glycolytic pathway can sustain the athletic performance during competition? rapid provision of energy to allow ● Recovery What is the evidence to support a particular meal timing, muscles to contract at a very high energy intake, and macronutrient intake for optimal rate for events lasting greater than athletic performance during recovery? 2 to 3 minutes. The oxidative pathway fuels events Figure 1. Specific topics and the respective questions used for the evidence analysis sections of lasting longer than 2 to 3 minutes. the American Dietetic Association, Dietitians of Canada, and American College of Sports Medicine The major substrates include muscle position on nutrition and athletic performance. and liver glycogen, intramuscular, blood, and adipose tissue triglycer- ances for consideration of study de- Conclusion statements were formu- ides, and negligible amounts of amino sign, the evidence-based analysis was lated summarizing the strength of evi- acids from muscle, blood, liver, and not limited to randomized controlled dence with respect to each question the gut. Examples of events for which trials. Study design preferences were (Figure 1). The strength of the evidence the major fuel pathway is the oxida- randomized controlled trials or clini- was graded using the following ele- tive pathway include a 1,500-meter cal controlled studies; large nonran- ments: quality, consistency across run, marathon, half-marathon, and domized observational studies; and studies, quantity, and generalizability. endurance cycling or 500 meter cohort, case-control studies. All sam- A more detailed description of the swimming events. As oxygen becomes ple sizes were included and study methodology used for this evidence- more available to the working muscle, drop out rate could not exceed 20%. based analysis may be found on the the body uses more of the aerobic (ox- The publication range for the evi- American Dietetic Association Web site idative) pathways and less of the an- dence-based analysis spanned 1995- at aerobic (phosphagen and glycolytic) 2006. If an author was included on hs.xsl/8099_ENU_HTML.htm. pathways. Only the aerobic pathway more than one review article or pri- can produce large amounts of ATP mary research article which were over time via the Kreb’s cycle and similar in content, the most recent ENERGY METABOLISM the electron transport system. The paper was accepted and earlier ver- Energy expenditure must equal en- greater dependence upon aerobic sions rejected. However, when an au- ergy intake to achieve energy bal- pathways does not occur abruptly, thor was included on more than one ance. The energy systems used during nor is one pathway ever relied on review article or primary research ar- exercise for muscular work include exclusively. The intensity, duration, ticle for which content differed, then the phosphagen and glycolytic (both frequency, type of activity, sex, and both reviews could be accepted for anaerobic) and the oxidative (aerobic) fitness level of the individual, as analysis. pathways. The phosphagen system is well as prior nutrient intake and en- The following exclusion criteria used for events lasting no longer than ergy stores, determine when the were applied to all identified studies: a few seconds and of high intensity. crossover from primarily aerobic to Adenosine triphosphate (ATP) and cre- anaerobic pathways occurs (2). ● adults older than age 40 years, atine phosphate provide the readily young adults younger than age 18 available energy present within the years, infants, children, and adoles- muscle. The amount of ATP present in Conversion of Energy Sources Over Time cents; skeletal muscles ( 5 mmol/kg wet Approximately 50% to 60% of energy ● settings not related to sports; weight) is not sufficient to provide a during 1 to 4 hours of continuous ex- ● nonathletes; continuous supply of energy, especially ercise at 70% of maximal oxygen ca- ● critical illness and other diseases at high exercise intensities. Creatine pacity is derived from carbohydrates and conditions; phosphate is an ATP reserve in muscle and the rest from free fatty acid oxi- ● drop out rates 20%; that can be readily converted to sustain dation (3). A greater proportion of en- ● publication before 1995; activity for 3 to 5 minutes (2). The ergy comes from oxidation of free ● studies by same author that were amount of creatine phosphate available fatty acids, primarily those from mus- similar in content; and in skeletal muscle is 4 times greater cle triglycerides as intensity of the ● articles not in English. than ATP, and therefore, is the pri- exercise decreases (3). Training does March 2009 ● Journal of the AMERICAN DIETETIC ASSOCIATION 511
  4. 4. not alter the total amount of energy expended but rather the proportion of Adult man energy derived from carbohydrates 662 9.53 (age in years) PAa [15.91 (weight in kilograms) 539.6 (height in meters)]. and fat (3). As a result of aerobic Adult woman training, the energy derived from fat 354 6.91 (age in years) PA [9.36 (weight in kilograms) 726 (height in meters)] increases and from carbohydrates de- creases. A trained individual uses a PA level greater percentage of fat than an un- 1.0-1.39 Sedentary, typical daily living activities (eg, household tasks, walking to bus). trained person does at the same work- 1.4-1.59 Low active, typical daily living activities plus 30-60 minutes of daily moderate load (2). Long-chain fatty aids derived activity (eg, walking at 5-7 km/h). from stored muscle triglycerides are 1.6-1.89 Active, typical daily living activities plus 60 minutes of daily moderate the preferred fuel for aerobic exercise activity. for individuals involved in mild- to 1.9-2.5 Very active, typical daily activities plus at least 60 minutes of daily moderate moderate-intensity exercise (4). activity plus an additional 60 minutes of vigorous activity or 120 minutes of moderate activity. ENERGY REQUIREMENTS Figure 2. The Dietary Reference Intake (DRI) method for estimating energy requirement for Meeting energy needs is a nutrition adults. Adapted from reference 17. aPA physical activity. priority for athletes. Optimum athletic performance is promoted by adequate particularly of the micronutrients ing metabolic rate. The two prediction energy intake. This section provides in- and may result in metabolic dysfunc- equations considered to most closely formation necessary to determine en- tions associated with nutrient defi- estimate energy expenditure are the ergy balance for an individual. Energy ciencies as well as lowered resting Cunningham equation (18) and the balance occurs when energy intake (the metabolic rate. The newer concept of Harris-Benedict equation (19). Be- sum of energy from foods, fluids, and energy availability, defined as dietary cause the Cunningham equation re- supplement products) equals energy intake minus exercise energy expen- quires that lean body mass be known, expenditure or the sum of energy ex- diture normalized to fat-free mass sports dietitians typically use the pended as basal metabolic rate; the (FFM), is the amount of energy avail- Harris-Benedict equation. To esti- thermic effect of food; and the thermic able to the body to perform all other mate total energy expenditure, basal effect of activity, which is the energy functions after exercise training ex- metabolic rate or resting metabolic expended in planned physical activity penditure is subtracted. Many re- rate is then multiplied by the appro- and nonexercise activity thermogenesis searchers have suggested that 30 priate activity factor of 1.8 to 2.3 (rep- (5). Spontaneous physical activity is kcal/kg FFM/day might be the lower resenting moderate to very heavy also included in the thermic effect of threshold of energy availability for physical activity levels, respectively). activity. women (12-15). Numeric guidelines such as these (8) Athletes need to consume enough Estimation of energy needs of ath- only provide an approximation of the energy to maintain appropriate letes and active individuals can be average energy needs of an individual weight and body composition while done using a variety of methods. The athlete. An alternative method for es- training for a sport (6). Although Dietary Guidelines for Americans timating exercise energy expenditure usual energy intakes for many in- 2005 (16) and the Dietary Reference is to use metabolic equivalents re- tensely training female athletes Intakes (15,17) provide energy recom- corded over a 24-hour period (20). Any might match those of male athletes mendations for men and women who of these methods can be used to esti- per kilogram body weight, some fe- are slightly to very active that are mate energy expenditure for the de- male athletes may consume less en- based on predictive equations devel- termination of energy intake require- ergy than they expend. Low energy oped using the doubly labeled water ments and provide a sports dietitian intake (eg, 1,800 to 2,000 kcal/day) technique, which can also be used to with a basis to guide an athlete or for female athletes is a major nutri- estimate energy needs of athletes active individual in meeting their en- tional concern because a persistent (Figure 2). ergy needs. state of negative energy balance can Energy expenditure for different lead to weight loss and disruption of types of exercise is dependent upon endocrine function (7-10). the duration, frequency, and inten- BODY COMPOSITION Inadequate energy intake relative sity of the exercise, the sex of the ath- Body composition and body weight to energy expenditure compromises lete, and prior nutritional status. He- are two of the many factors that con- performance and negates the benefits redity, age, body size, and FFM also tribute to optimal exercise perfor- of training. With limited energy in- influence energy expenditure. The mance. Taken together, these two fac- take, fat and lean tissue will be used more energy used in activity, the tors may affect an athlete’s potential for fuel by the body. Loss of lean tis- more energy needed to achieve energy for success for a given sport. Body sue mass results in the loss of balance. weight can influence an athlete’s strength and endurance, as well as Typical laboratory facilities are speed, endurance, and power, compromised immune, endocrine, usually not equipped to determine to- whereas body composition can affect and musculoskeletal function (11). In tal energy expenditure. Therefore, an athlete’s strength, agility, and ap- addition, chronically low energy in- predictive equations are often used to pearance. A lean body (ie, one with take results in poor nutrient intake, estimate basal metabolic rate or rest- greater muscle/fat ratio) is often ad- 512 March 2009 Volume 109 Number 3
  5. 5. vantageous in sports where speed is ter weighing, dual-energy x-ray ab- Kinanthropometry techniques (26) as involved. sorptiometry and air displacement efforts are underway to standardize Athletic performance cannot be ac- plethysmography are Level II tech- measures worldwide. The US Olympic curately predicted based solely on niques, and skinfold measurements Committee advocates using the sum of body weight and composition given and bioelectrical impedance analysis seven skinfolds (millimeters) based on that many factors affect body compo- (BIA) are Level III techniques. Level International Society for Advances in sition (21). Some sports dictate that II and Level III techniques are used Kinanthropometry landmarks, mark- athletes make changes in body weight in practice by sports dietitians. ing skinfold sites on the body, reporting and composition that may not be best Underwater weighing, once consid- duplicate measures, and communicat- for the individual athlete. Athletes ered the criterion standard, is no longer ing the results as a range, rather than who participate in weight-class common. dual-energy x-ray absorpti- percentage body fat. sports—such as wrestling or light- ometry, originally developed to assess BIA is based on the principle that weight rowing—may be required to bone mineral density, can be used for an electrical signal is more easily con- lose or gain weight to qualify for a body composition analysis (21). Al- ducted through lean tissue than fat or specific weight category. Athletes who though dual-energy x-ray absorptiom- bone (22). Fat mass is estimated by participate in body conscious sports etry is fairly accurate, quick, and non- subtracting the BIA determined esti- such as dance, gymnastics, figure invasive, the cost of and access to the mate of FFM from total body mass. skating, or diving, may be pressured instrument limits its utility in practice. Whole body resistance to the flow to lose weight and body fat to have a Air displacement plethysmography of an electrical current conducted lean physique, although their current (BodPod, Life Measurement, Inc, Con- through the body by electrodes placed weight for health and performance is cord, CA) is also used to determine on wrists and ankles can provide appropriate. With extreme energy re- body composition by body density (22), fairly accurate estimates of total body strictions, losses of both muscle and and body fat percentage is calculated water and FFM (22). BIA is depen- fat mass may adversely influence an using the Siri (23) or Brozek and col- dent on a number of factors that can athlete’s performance. leagues (24) equations. Although this cause error in the measurement and Individualized assessment of an method provides valid and reliable as- must be taken into account to obtain a athlete’s body composition and body sessment of body composition, it may fairly accurate estimate. Hydration weight or body image may be advan- underestimate body fat in adults and status is the most important factor tageous for improvement of athletic children by 2% to 3% (25). that may alter the estimated percent- performance. Age, sex, genetics, and Two of the most commonly used age body fat. The prediction accuracy the requirements of the sport are fac- Level III methods are skinfold mea- of BIA is similar to skinfold assess- tors that influence an individual ath- surements and BIA. In addition to ments but BIA may be preferable be- lete’s body composition. An optimal measures of body weight, height, cause it does not require the technical competitive body weight and relative wrist and girth circumferences, skin- skill associated with skinfold mea- body fatness should be determined fold measurements are routinely used surements (27). Currently, upper and when an athlete is healthy and per- by sports dietitians to assess body lower body impedance devices have forming at his or her best. composition. Usually, seven skinfold been developed but have not been Methodology and equipment to per- sites are used, including abdominal, evaluated in an athletic population. form body composition assessments biceps, front thigh, medial calf, sub- must be accessible and cost effective. scapular, supraspinale, and triceps. Not all of the following methods meet The standard techniques and defini- Body Composition and Sports these criteria for the practitioner. In tions of each of these sites are pro- Performance addition, athletes and coaches should vided by Heymsfield and colleagues Body fat percentage of athletes varies know that there are errors associated and Marfell-Jones and colleagues depending on the sex of the athlete with all body composition techniques (22). Prediction equations using skin- and the sport. The estimated minimal and that it is not appropriate to set a fold measurements to determine body level of body fat compatible with specific body fat percentage goal for fat content are numerous (22). Ap- health is 5% for men and 12% for an individual athlete. Rather, a range proximately 50% to 70% of the vari- women (22); however, optimal body of target percentages of body fat val- ance in body density is accounted for fat percentages for an individual ath- ues should be recommended. by this measurement. In addition, lete may be much higher than these population differences limit the abil- minimums and should be determined ity to interchange the prediction on an individual basis. The Interna- Assessment Methodology equations, standardization of skinfold tional Society for Advances in Kinan- Three levels of assessment tech- sites varies, and skinfold measure- thropometry sum of seven skinfolds niques are used to assess body com- ment techniques vary from investiga- indicates that the range of values for position (22). Direct assessment tor to investigator. Even the skinfold the athletic population is 30 to 60 mm based on analysis of cadavers, al- caliper is a source of variability (22). for men and 40 to 90 mm for women though not used in clinical practice, is Despite the inherent problems of (26). Body composition analysis designated as a Level 1 technique. skinfold measurement, this technique should not be used as a criterion for The other two technique levels are remains a method of choice because it selection of athletes for athletic indirect assessments (Level II) and is convenient and inexpensive. The teams. Weight management inter- doubly indirect assessments (Level US Olympic Committee is using the ventions should be thoughtfully de- III). Hydrodensitometry, or underwa- International Society for Advances in signed to avoid detrimental outcomes March 2009 ● Journal of the AMERICAN DIETETIC ASSOCIATION 513
  6. 6. Setting and monitoring goals ● Set realistic weight and body composition goals. Ask the athlete: What is the maximum weight that you would find acceptable? What was the lowest weight you maintained without constant dieting? How did you derive your goal weight? At what weight and body composition do you perform best? ● Encourage less focus on the scale and more on healthful habits such as stress management and making good food choices. ● Monitor progress by measuring changes in exercise performance and energy level, the prevention of injuries, normal menstrual function, and general overall well-being. ● Help athletes to develop lifestyle changes that maintain a healthful weight for themselves—not for their sport, for their coach, for their friends, for their parents, or to prove a point. Suggestions for food intake ● Low energy intake will not sustain athletic training. Instead, decreases in energy intake of 10% to 20% of normal intake will lead to weight loss without the athlete feeling deprived or overly hungry. Strategies such as substituting lower-fat foods for whole-fat foods, reducing intake of energy-dense snacks, portion awareness, and doing activities other than eating when not hungry can be useful. ● If appropriate, athletes can reduce fat intake but need to know that a lower-fat diet will not guarantee weight loss unless a negative energy balance (reduced energy intake and increased energy expenditure) is achieved. Fat intake should not be decreased below 15% of total energy intake because some fat is essential for good health. ● Emphasize increased intake of whole grains and cereals, and legumes. ● Five or more daily servings of fruits and vegetables provide nutrients and fiber. ● Dieting athletes should not skimp on protein and need to maintain adequate calcium intakes. Accordingly, use of low-fat dairy products and lean meats, fish, and poultry is suggested. ● A variety of fluids— especially water—should be consumed throughout the day, including before, during, and after exercise. Dehydration as a means of reaching a body-weight goal is contraindicated. Other weight management strategies ● Advise athletes against skipping meals (especially breakfast) and allowing themselves to become overly hungry. They should be prepared for times when they might get hungry, including keeping nutritious snacks available for those times. ● Athletes should not deprive themselves of favorite foods or set unrealistic dietary rules or guidelines. Instead, dietary goals should be flexible and achievable. Athletes should remember that all foods can fit into a healthful lifestyle. Developing list of “good” and “bad” foods is discouraged. ● Help athletes identify their own dietary weaknesses and plan strategies for dealing with them. ● Remind athletes that they are making lifelong dietary changes to sustain a healthful weight and optimal nutritional status rather than going on a short-term diet. Figure 3. Weight management strategies for athletes. (Adapted from: Manore MM. Chronic dieting in active women: What are the health consequences? Women’s Health Issues. 1996;6:332-341. Copyright 1996, with permission from Elsevier.) with specific regard for performance, in the 2005 Dietary Guidelines (16) and not be sufficient to maintain optimal as well as body composition (ie, loss of Eating Well with Canada’s Food Guide carbohydrate stores (4 to 5 g/kg or 1.8 lean body mass). See Figure 3 for (28). Although high-carbohydrate diets to 2.3 g/lb) in a 60-kg (132 lb) athlete. practical guidelines for weight man- (more than 60% of energy intake) have agement of athletes. been advocated in the past, caution is Protein recommended in using specific percent- Conclusion Statement. Four studies have Protein metabolism during and fol- ages as a basis for meal plans for ath- lowing exercise is affected by sex, age, reported inconclusive findings related to letes. For example, when energy intake the effects of energy and protein restric- intensity, duration, and type of exer- is 4,000 to 5,000 kcal/day, even a diet cise, energy intake, and carbohydrate tion on athletic performance, but carbo- containing 50% of energy from carbo- hydrate restriction has been shown to be availability. More detailed reviews of hydrate will provide 500 to 600 g car- these factors and their relationship to detrimental. For weight class athletes, bohydrate (or approximately 7 to 8 g/kg protein metabolism and needs of ac- two studies show that weight loss preced- [3.2 to 3.6 g/lb] for a 70-kg [154 lb] ath- tive individuals can be found else- ing athletic competition may have no sig- lete), an amount sufficient to maintain where (30,31). The current RDA is 0.8 nificant effect on measures of perfor- mance, depending on refeeding protocol. muscle glycogen stores from day to day g/kg body weight and the Acceptable Evidence Grade III Limited (www. (29). Similarly, if protein intake for this Macronutrient Distribution Range for plan was 10% of energy intake, abso- protein intake for adults older than conclusion_statement_id 250448). lute protein intake (100 to 125 g/day) age 18 years is 10% to 35% of total could exceed the recommended protein energy (15). Because there is not a intake for athletes (1.2 to 1.7 g/kg/day strong body of evidence documenting MACRONUTRIENT REQUIREMENTS FOR or 84 to 119 g in a 70-kg athlete). Con- that additional dietary protein is EXERCISE versely, when energy intake is less needed by healthy adults who under- Athletes do not need a diet substan- than 2,000 kcal/day, a diet providing take endurance or resistance exer- tially different from that recommended 60% of energy from carbohydrate may cise, the current Dietary Reference 514 March 2009 Volume 109 Number 3
  7. 7. Intakes for protein and amino acids supplementation with individual pathways where micronutrients are does not specifically recognize the amino acids (37,38) more recent work required, and exercise training may unique needs of routinely active in- has shown that intact, high-quality result in muscle biochemical adapta- dividuals and competitive athletes. proteins such as whey, casein, or soy tions that increase micronutrient However, recommending protein in- are effectively used for the mainte- needs. Routine exercise may also in- takes in excess of the RDA to main- nance, repair, and synthesis of skele- crease the turnover and loss of these tain optimum physical performance is tal muscle proteins in response to micronutrients from the body. As a commonly done in practice. training (39). Protein or amino acids result, greater intakes of micronutri- Endurance Athletes. An increase in pro- consumed in close proximity to ents may be required to cover in- tein oxidation during endurance exer- strength and endurance exercise can creased needs for building, repair, cise, coupled with nitrogen balance enhance maintenance of, and net and maintenance of lean body mass in studies, provides the basis for recom- gains in, skeletal muscle (39,40). Be- athletes (46). mending increased protein intakes for cause protein or amino acid supple- The most common vitamins and recovery from intense endurance train- mentation has not been shown to pos- minerals found to be of concern in ing (32). Nitrogen balance studies itively influence athletic performance athletes’ diets are calcium and vita- suggest that dietary protein intake (41,42), recommendations regarding min D, the B vitamins, iron, zinc, necessary to support nitrogen balance protein supplementation are conser- magnesium, as well as some antioxi- in endurance athletes ranges from 1.2 vative and directed primarily at opti- dants such as vitamins C and E, beta to 1.4 g/kg/day (29-31). These recom- mizing the training response to and carotene, and selenium (46-50). Ath- mendations remain unchanged even the recovery period following exer- letes at greatest risk for poor micro- though recent studies have shown cise. From a practical perspective, it nutrient status are those who restrict that protein turnover may become is important to conduct a thorough energy intake or have severe weight more efficient in response to endur- nutrition assessment specific to an loss practices, who eliminate one or ance exercise training (29,32). Ultra- athlete’s goals before recommending more of the food groups from their endurance athletes who engage in protein powders and amino acid sup- diet, or who consume unbalanced and continuous activity for several hours plements to athletes. low micronutrient-dense diets. These or consecutive days of intermittent athletes may benefit from a daily exercise should also consume protein multivitamin/mineral supplement. Fat Use of vitamin and mineral supple- at, or slightly above 1.2 to 1.4 g/kg/ Fat is a necessary component of a nor- ments does not improve performance day (32). Energy balance, or the con- mal diet, providing energy and essen- in individuals consuming nutrition- sumption of adequate energy, partic- tial elements of cell membranes and ally adequate diets (46-48,50). ularly carbohydrates, to meet those expended, is important to protein me- associated nutrients such as vitamins tabolism so that amino acids are A, D, and E. The Acceptable Macro- nutrient Distribution Range for fat is B Vitamins: Thiamin, Riboflavin, Niacin, B-6, spared for protein synthesis and not Pantothenic Acid, Biotin, Folate, and B-12 oxidized to assist in meeting energy 20% to 35% of energy intake (17). The 2005 Dietary Guidelines (16) and Adequate intake of B vitamins is im- needs (33,34). In addition, discussion Eating Well with Canada’s Food portant to ensure optimum energy continues as to whether sex differ- Guide (28) make recommendations production and the building and re- ences in protein-related metabolic re- that the proportion of energy from pair of muscle tissue (48,51). The B- sponses to exercise exist (35,36). fatty acids be 10% saturated, 10% complex vitamins have two major Strength Athletes. Resistance exercise polyunsaturated, and 10% monoun- functions directly related to exercise. may necessitate protein intake in ex- saturated and include sources of es- Thiamin, riboflavin, niacin, pyridox- cess of the RDA, as well as that needed sential fatty acids. Athletes should ine (B-6), pantothenic acid, and biotin for endurance exercise, because addi- follow these general recommenda- are involved in energy production tional protein, essential amino acids in tions. Careful evaluation of studies during exercise (46,51), whereas fo- particular, is needed along with suffi- suggesting a positive effect of con- late and B-12 are required for the pro- cient energy to support muscle growth suming diets for which fat provides duction of red blood cells, for protein (30,31). This is particularly true in the 70% of energy intake on athletic synthesis, and in tissue repair and early phase of strength training when performance (43,44) does not support maintenance including the central the most significant gains in muscle this concept (45). nervous system. Of the B vitamins, size occurs. The amount of protein riboflavin, pyridoxine, folate and B-12 needed to maintain muscle mass may are frequently low in female athletes’ be lower for individuals who routinely VITAMINS AND MINERALS diets, especially those who are vege- resistance train due to more efficient Micronutrients play an important tarian or have disordered eating pat- protein utilization (30,31). Recom- role in energy production, hemoglobin terns (47,48). mended protein intakes for strength- synthesis, maintenance of bone Limited research has been con- trained athletes range from approxi- health, adequate immune function, ducted to examine whether exercise mately 1.2 to 1.7 g/kg/day (30,32). and protection of body against oxida- increases the need for the B-complex Protein and Amino Acid Supplements. tive damage. They assist with synthe- vitamins (46,48). Some data suggest High-protein diets have been popular sis and repair of muscle tissue during that exercise may increase the need throughout history. Although earlier recovery from exercise and injury. Ex- for these vitamins as much as twice investigations in this area involved ercise stresses many of the metabolic the current recommended amount March 2009 ● Journal of the AMERICAN DIETETIC ASSOCIATION 515
  8. 8. (48); however, these increased needs dant supplements enhance physical quate dietary calcium and vitamin D can generally be met with higher en- performance (49,50,64,66). Athletes at increase the risk of low bone-mineral ergy intakes. Although short-term greatest risk for poor antioxidant in- density and stress fractures. Female marginal deficiencies of B vitamins takes are those following a low-fat diet, athletes are at greatest risk for low have not been observed to affect per- restricting energy intakes, or limiting bone-mineral density if energy in- formance, severe deficiency of B-12, dietary intakes of fruits, vegetables, takes are low, dairy products and folate, or both may result in anemia and whole grains (29,66). other calcium-rich foods are inade- and reduced endurance performance The evidence that a combination quate or eliminated from the diet, and (46,47,52). Therefore, it is important of antioxidants or single antioxi- menstrual dysfunction is present that athletes consume adequate dants such as vitamin E may be (47,52,55,71-73). amounts of these micronutrients to helpful in reducing inflammation Supplementation with calcium and support their efforts for optimal per- and muscle soreness during recov- vitamin D should be determined after formance and health. ery from intense exercise remains nutrition assessment. Current recom- unclear (42,67). Although the ergo- mendations for athletes with disor- genic potential of vitamin E with dered eating, amenorrhea, and risk Vitamin D regard to physical performance has for early osteoporosis are 1,500 mg Vitamin D is required for adequate not been clearly documented, endur- elemental calcium and 400 to 800 IU calcium absorption, regulation of se- ance athletes may have a higher of vitamin D per day (50,72,73). rum calcium and phosphorus levels, need for this vitamin. Indeed, vita- Iron. Iron is required for the forma- and promotion of bone health. Vita- min E supplementation has been tion of oxygen-carrying proteins, he- min D also regulates the development shown to reduce lipid peroxidation moglobin and myoglobin, and for en- and homeostasis of the nervous sys- during aerobic/endurance exercise zymes involved in energy production tem and skeletal muscle (53-55). Ath- and have a limited effect with (50,74). Oxygen carrying capacity is letes who live at northern latitudes or strength training (66). There is essential for endurance exercise as who train primarily indoors through- some evidence that vitamin E may well as normal function of the ner- out the year, such as gymnasts and attenuate exercise-induced DNA damage and enhance recovery in vous, behavioral, and immune sys- figure skaters, are at risk for poor vi- certain active individuals; however, tems (64,74). Iron depletion (low iron tamin D status, especially if they do more research is needed (66). Ath- stores) is one of the most prevalent not consume foods fortified with vita- letes should be advised not to exceed nutrient deficiencies observed among min D (50,56,57). These athletes would benefit from supplementation the Tolerable Upper Intake Levels athletes, especially women (75). Iron with vitamin D at the Dietary Refer- for antioxidants because higher deficiency, with or without anemia, ence Intake level (5 g/day or 200 IU doses could be pro-oxidative with can impair muscle function and limit for ages 19 to 49 years) (54,56,58-61). potential negative effects (46,64,68). work capacity (47,58,75,76). Iron re- A growing number of experts advo- Vitamin C supplements do not ap- quirements for endurance athletes, es- cate that the RDA for vitamin D is not pear to have an ergogenic effect if the pecially distance runners, are in- adequate (53,62,63). diet provides adequate amounts of creased by approximately 70% (58,74). this nutrient. Because strenuous and Athletes who are vegetarian or regular prolonged exercise has been shown to blood donors should aim for an iron in- Antioxidants: Vitamins C and E, Beta increase the need for vitamin C, phys- take greater than their respective RDA Carotene, and Selenium ical performance can be compromised (ie, 18 mg and 8 mg, for women and The antioxidant nutrients, vitamins C with marginal vitamin C status or de- men, respectively) (58,75). and E, beta carotene, and selenium, ficiency. Athletes who participate in The high incidence of iron depletion play important roles in protecting cell habitual prolonged, strenuous exer- among athletes is usually attributed to membranes from oxidative damage. cise should consume 100 to 1,000 mg inadequate energy intake. Other fac- Because exercise can increase oxygen vitamin C daily (47,69,70). tors that can affect iron status include consumption by 10- to 15-fold, it has vegetarian diets that have poor iron been hypothesized that chronic exer- availability, periods of rapid growth, cise produces a constant “oxidative Minerals: Calcium, Iron, Zinc, and training at high altitudes, increased stress” on the muscles and other cells Magnesium iron losses in sweat, feces, urine, men- (49) leading to lipid peroxidation of The primary minerals low in the diets strual blood, intravascular hemolysis, membranes. Although acute exercise of athletes, especially female athletes, foot-strike hemolysis, regular blood do- may increase levels of lipid peroxide are calcium, iron, zinc, and magne- nation, or injury (50,75,77). Athletes, byproducts (64), habitual exercise has sium (47). Low intakes of these min- especially women, long-distance run- been shown to result in an augmented erals are often due to energy restric- ners, adolescents, and vegetarians antioxidant system and reduced lipid tion or avoidance of animal products should be screened periodically to as- peroxidation (50,65). Thus, a well- (55). sess and monitor iron status (75,77,78). trained athlete may have a more devel- Calcium. Calcium is especially impor- Because reversing iron deficiency oped endogenous antioxidant system tant for growth, maintenance, and re- anemia can require 3 to 6 months, it than a sedentary person. Whether ex- pair of bone tissue; maintenance of is advantageous to begin nutrition in- ercise increases the need for antioxi- blood calcium levels, regulation of tervention before iron deficiency ane- dant nutrients remains controversial. muscle contraction, nerve conduction, mia develops (47,75). Although de- There is little evidence that antioxi- and normal blood clotting. Inade- pleted iron stores (low serum ferritin) 516 March 2009 Volume 109 Number 3
  9. 9. are more prevalent in female ath- difficult to measure because clear as- adequate for maintaining normal po- letes, the incidence of iron deficiency sessment criteria have not been es- tassium status among athletes (32,83). anemia in athletes is similar to that tablished and plasma zinc concentra- of the nonathlete female population tions may not reflect changes in whole (50,75,77). Chronic iron deficiency, body zinc status (47,79). Decreases in HYDRATION with or without anemia, that results cardiorespiratory function, muscle Being well hydrated is an important from consistently poor iron intake can strength, and endurance have been consideration for optimal exercise negatively affect health, physical and noted with poor zinc status (47). The performance. Because dehydration mental performance, and warrants Tolerable Upper Intake Level for zinc increases the risk of potentially life- prompt medical intervention and is 40 mg (74). Athletes should be cau- threatening heat injury such as heat monitoring (76,78). tioned against single dose zinc sup- stroke, athletes should strive for eu- Some athletes may experience a plements because they often exceed hydration before, during, and after transient decrease in serum ferritin this amount and unnecessary zinc exercise. Dehydration (loss of 2% and hemoglobin at the initiation of supplementation may lead to low body weight) can compromise aerobic training due to hemodilution subse- high-density lipoprotein cholesterol exercise performance, particularly in quent to an increase in plasma vol- and nutrient imbalances by interfer- hot weather, and may impair mental/ ume known as “dilutional” or “sports ing with absorption of other nutrients cognitive performance (83). anemia” and may not respond to nu- such as iron and copper (47). Further- The American College of Sports trition intervention. These changes more, the benefits of zinc supplemen- Medicine’s Position Stand on Exercise appear to be a beneficial adaptation tation to physical performance have and Fluid Replacement (83) provides to aerobic training that do not nega- not been established. a comprehensive review of the re- tively affect performance (50). Magnesium. Magnesium plays a variety search and recommendations for In athletes who are iron deficient, of roles in cellular metabolism (eg, gly- maintaining hydration before, dur- iron supplementation not only im- colysis, fat, and protein metabolism), ing, and after exercise. In addition, proves blood biochemical measures and regulates membrane stability and the American College of Sports Med- and iron status but also increases neuromuscular, cardiovascular, im- icine has published position stands mune, and hormonal functions (47,55). specific to special environmental con- work capacity as evidenced by in- Magnesium deficiency impairs endur- ditions (84,85). The major points from creasing oxygen uptake, reducing ance performance by increasing oxygen these position stands are the basis for heart rate, and decreasing lactate requirements to complete submaximal the following recommendations. concentration during exercise (47). There is some evidence that athletes exercise. Athletes in weight-class and who are iron deficient but do not have body conscious sports such as wres- Fluid and Electrolyte Recommendations anemia may benefit from iron supple- tling, ballet, gymnastics, as well as ten- nis, have been reported to consume in- Before Exercise. At least 4 hours before mentation (50,75). Recent findings exercise, individuals should drink provide additional support for im- adequate dietary magnesium. Athletes should be educated about good food about 5 to 7 mL/kg body weight ( 2 to proved performance (eg, less skeletal 3 mL/lb) of water or a sport beverage. muscle fatigue) when iron supple- sources of magnesium. In athletes with low magnesium status, supplementa- This would allow enough time to op- mentation was prescribed as 100 mg timize hydration status and for excre- ferrous sulfate for 4-6 weeks (76). Im- tion might be beneficial (47). tion of any excess fluid as urine. Hy- proving work capacity and endur- perhydration with fluids that expand ance, increasing oxygen uptake, re- Sodium, Chloride, and Potassium the extra- and intracellular spaces duced lactate concentrations, and (eg, water and glycerol solutions) will Sodium is a critical electrolyte, partic- reduced muscle fatigue are benefits of greatly increase the risk of having to ularly for athletes with high sweat improved iron status (50). void during competition (83) and pro- losses (80-83). Many endurance ath- Zinc. Zinc plays a role in growth, letes will require much more than the vides no clear physiologic or perfor- building and repair of muscle tissue, Tolerable Upper Intake Level for so- mance advantage over euhydration. energy production, and immune sta- dium (2.3 g/day) and chloride (3.6 This practice should be discouraged tus. Diets low in animal protein, high g/day). Sports drinks containing so- (83). in fiber, and vegetarian diets, in par- dium (0.5 to 0.7 g/L) and potassium During Exercise. Athletes dissipate heat ticular, are associated with decreased (0.8 to 2.0 g/L), as well as carbohy- produced during physical activity by zinc intake (50,52). Zinc status has drate, are recommended for athletes radiation, conduction, convection, and been shown to directly affect thyroid especially in endurance events ( 2 by vaporization of water. In hot, dry hormone levels, basal metabolic rate, hours) (50,80,82,83). environments, evaporation accounts and protein use, which in turn can Potassium is important for fluid and for more than 80% of metabolic heat negatively affect health and physical electrolyte balance, nerve transmis- loss. Sweat rates for any given activity performance (50). Survey data indi- sion, and active transport mechanisms. will vary according to ambient temper- cate that a large number of North During intense exercise, plasma potas- ature, humidity, body weight, genetics, Americans have zinc intakes below sium concentrations tend to decline to a heat acclimatization state, and meta- recommended levels (74,75,79). Ath- lesser degree than sodium. A diet rich bolic efficiency. Depending on the sport letes, particularly women, are also at in a variety of fresh vegetables, fruits, and condition, sweat rates can range risk for zinc deficiency (79). The affect nuts and seeds, dairy foods, lean meats, from as little as 0.3 to as much as 2.4 of low zinc intakes on zinc status is and whole grains is usually considered liters per hour (83). In addition to wa- March 2009 ● Journal of the AMERICAN DIETETIC ASSOCIATION 517
  10. 10. ter, sweat also contains substantial but Although some individuals begin ex- lytes lost during exercise. Rapid and variable amounts of sodium. The aver- ercise euhydrated and dehydrate over complete recovery from excessive de- age concentration of sodium in sweat an extended duration, athletes in hydration can be accomplished by approximates 1 g/L (50 mmol/L) (al- some sports might start training or drinking at least 16 to 24 oz (450 to though concentrations vary widely). competition in a dehydrated state be- 675 mL) of fluid for every pound (0.5 There are modest amounts of potas- cause the interval between exercise kg) of body weight lost during exer- sium and small amounts of minerals sessions is inadequate for full rehy- cise. Consuming rehydration bever- such as magnesium and chloride lost in dration (82). Another factor that may ages and salty foods at meals/snacks sweat. predispose an athlete to dehydration will help replace fluid and electrolyte The intent of drinking during exer- is making weight as a prerequisite for losses (83). cise is to avert a water deficit in ex- a specific sport or event. Hypohydra- cess of 2% of body weight. The tion, a practice of some athletes com- amount and rate of fluid replacement peting in weight class sports (eg, Special Environmental Conditions is dependent on an individual ath- wrestling, boxing, lightweight crew, Hot and Humid Environments. The risk lete’s sweat rate, exercise duration, and martial arts), can occur when for dehydration and heat injury in- and opportunities to drink (83). Read- athletes dehydrate themselves before creases dramatically in hot, humid ers are referred to the American Col- beginning a competitive event. Hypo- environments (84). When the ambient lege of Sports Medicine position stand hydration can develop by fluid restric- temperature exceeds body tempera- for specific recommendations related tion, certain exercise practices, di- ture, heat cannot be dissipated by ra- to body size, sweat rates, types of uretic use, or sauna exposure before diation. Moreover, the potential to work, and encouraged to individual- an event. In addition, fluid deficits dissipate heat by evaporation of ize hydration protocols when possible may span workouts for athletes who sweat is substantially reduced when (83). Routine measurement of pre- participate in multiple or prolonged the relative humidity is high. There is and postexercise body weights will daily sessions of exercise in the heat a very high risk of heat illness when assist practitioners in determining (84). temperature and humidity are both sweat rates and customizing fluid re- Hyponatremia (serum sodium con- high. If competitive events occur un- placement programs for individual centration 130 mEq/L [ 130 mmol/ der these conditions, it is necessary to athletes (83). L]) can result from prolonged, heavy take every precaution to assure that Consumption of beverages contain- sweating with failure to replace so- athletes are well hydrated, have am- ing electrolytes and carbohydrates dium, or excessive water intake. Hy- ple access to fluids, and are monitored can help sustain fluid and electrolyte ponatremia is more likely to develop for heat-related illness. balance and endurance exercise per- in novice marathoners who are not formance (83). The type, intensity, Cold Environments. It is possible for de- lean, run slowly, sweat less or con- hydration to occur in cool or cold and duration of exercise and environ- sume excess water before, during, or mental conditions will alter the need weather (85). Factors contributing to after an event (83). dehydration in cold environments in- for fluids and electrolytes. Fluids con- Skeletal muscle cramps are associ- taining sodium and potassium help clude respiratory fluid losses, as well ated with dehydration, electrolyte as sweat losses that occur when insu- replace sweat electrolyte losses, deficits, and muscle fatigue. Non– whereas sodium stimulates thirst and lated clothing is worn during intense heat acclimatized American football exercise. Dehydration can also occur fluid retention, and carbohydrates players commonly experience dehy- because of low rates of fluid ingestion. provide energy. Beverages containing dration and muscle cramping partic- If an athlete is chilled and available 6% to 8% carbohydrate are recom- ularly during formal preseason prac- fluids are cold, the incentive to drink mended for exercise events lasting tice sessions in late summer. Athletes may be reduced. Finally, removal of longer than 1 hour (83). participating in tennis matches, long multiple layers of clothing to urinate Fluid balance during exercise is not cycling races, late-season triathlons, may be inconvenient and difficult for always possible because maximal sweat rates exceed maximal gastric soccer, and beach volleyball are also some athletes, especially women, and emptying rates that in turn limit fluid susceptible to dehydration and mus- they may voluntarily limit fluid in- absorption and most often rates of cle cramping. Muscle cramps also oc- take (86). fluid ingestion by athletes during ex- cur in winter-sport athletes such as Altitude. Fluid losses beyond those as- ercise fall short of amounts that can cross-country skiers and ice-hockey sociated with any exercise performed be emptied from the stomach and ab- players. Muscle cramps are more may occur at altitudes 2,500 m sorbed by the gut. Gastric emptying is common in profuse sweaters who ex- (8,200 ft) consequent to mandatory maximized when the amount of fluid perience large sweat sodium losses diuresis and high respiratory water in the stomach is high and reduced (83). losses, accompanied by decreased ap- with hypertonic fluids or when carbo- After Exercise. Because many athletes petite. Respiratory water losses may hydrate concentration is 8%. do not consume enough fluids during be as high as 1,900 mL (1.9 L) per day Disturbances of fluid and electro- exercise to balance fluid losses, they in men and 850 mL (0.85 L) per day in lyte balance that can occur in athletes complete their exercise session dehy- women (87,88). Total fluid intake at include dehydration, hypohydration, drated to some extent. Given ade- high altitude approaches 3 to 4 L per and hyponatremia (83). Exercise-in- quate time, intake of normal meals day to promote optimal kidney func- duced dehydration develops because and beverages will restore hydration tion and maintain urine output of fluid losses that exceed fluid intake. status by replacing fluids and electro- 1.4 L in adults (87). 518 March 2009 Volume 109 Number 3
  11. 11. THE TRAINING DIET fore competition results in improved whether the glycemic index of carbo- The fundamental differences between muscle glycogen concentrations and/or hydrate in the pre-exercise meal af- an athlete’s diet and that of the gen- significant improvements in athletic per- fects performance (92,99-102). eral population are that athletes re- formance. Two studies reported no addi- Although the above guidelines are quire additional fluid to cover sweat tional performance benefits when con- sound and effective, the athlete’s in- losses and additional energy to fuel suming levels above 6 g carbohydrate/kg dividual needs must be emphasized. physical activity. As discussed ear- body weight. Two studies report sex dif- Some athletes consume and enjoy a lier, it is appropriate for much of the ferences; women may have less ability to substantial meal (eg, pancakes, juice, additional energy to be supplied as increase muscle glycogen concentrations and scrambled eggs) 2 to 4 hours be- carbohydrate. The proportional in- through increased carbohydrate con- fore exercise or competition; however, crease in energy requirements ap- sumption, especially when energy intake others may suffer severe gastrointes- pears to exceed the proportional in- is insufficient. One study based on the tinal distress following such a meal crease in needs for most other consumption of a high-fat diet ( 65% of and need to rely on liquid meals. Ath- nutrients. Accordingly, as energy re- energy) for 10 days followed by a high- letes should always ensure that they quirements increase, athletes should carbohydrate diet ( 65% of energy) for 3 know what works best for themselves first aim to consume the maximum days reported a significant improvement by experimenting with new foods and number of servings appropriate for in athletic performance. Nine studies re- beverages during practice sessions their needs from carbohydrate-based port no significant effects of macronutri- and planning ahead to ensure they food groups (ie, bread, cereals and ent composition on athletic performance will have access to these foods at the grains, legumes, milk/alternatives, during the training period and week appropriate time. vegetables, and fruits). Energy needs prior to competition. Evidence Grade Conclusion Statement. Nineteen studies for many athletes will exceed the II Fair ( investigating the consumption of a range amount of energy (kilocalories per conclusion.cfm?conclusion_statement_ of macronutrient composition during the id 250447). 24 hours before competition on athletic day) in the upper range of servings for these food groups. Conversely, ath- performance were evaluated. Of eight letes who are small and/or have lower studies, six reported no significant effect Pre-Exercise Meal of meal consumption 90 minutes to 4 energy needs will need to pay greater attention to making nutrient-dense Eating before exercise, as opposed to hours before trials on athletic perfor- food choices to obtain adequate carbo- exercising in the fasting state, has been mance. Six studies that focused on the hydrate, protein, essential fats, and shown to improve performance (89,90). consumption of food or beverage within micronutrients. The meal or snack consumed before the hour before competition reported no competition or an intense workout significant effects on athletic perfor- With regard to the timing of meals should prepare athletes for the upcom- mance, despite hyperglycemia, hyper- and snacks, common sense dictates ing activity, and leave the individual insulinemia, increased carbohydrate that food and fluid intake around neither hungry nor with undigested oxidation, and reduced free fatty acid workouts be determined on an indi- food in the stomach. Accordingly, the availability. Variations in research meth- vidual basis with consideration for an following general guidelines for meals odology on glycemic index of meals con- athlete’s gastrointestinal characteris- and snacks should be used: sufficient sumed prior to competition have led to tics as well as the duration and inten- fluid should be ingested to maintain inconclusive findings. Evidence Grade sity of the workout. For example, an hydration, foods should be relatively II Fair ( athlete might tolerate a snack con- low in fat and fiber to facilitate gastric conclusion.cfm?conclusion_statement_ sisting of milk and a sandwich 1 hour emptying and minimize gastrointesti- id 250452). before a low-intensity workout, but nal distress, high in carbohydrate to would be uncomfortable if the same maintain blood glucose and maximize meal was consumed before a very glycogen stores, moderate in protein, During Exercise hard effort. Athletes in heavy train- and familiar to the athlete. Current research supports the ben- ing or doing multiple daily workouts The size and timing of the pre-ex- efit of carbohydrate consumption in may need to eat more than three ercise meal are interrelated. Because amounts typically provided in sport meals and three snacks per day and most athletes do not like to compete drinks (6% to 8%) to endurance per- should consider every possible eating on a full stomach, smaller meals formance in events lasting 1 hour or occasion. These athletes should con- should be consumed in closer proxim- less (103-105), especially in athletes sider eating in close proximity to the ity to the event to allow for gastric who exercise in the morning after an end of a workout, having more than emptying, whereas larger meals can overnight fast when liver glycogen one afternoon snack, or eating a sub- be consumed when more time is avail- levels are decreased. Providing exog- stantial snack before bed. able before exercise or competition. enous carbohydrate during exercise Conclusion Statement. Twenty-three stud- Amounts of carbohydrate shown to helps maintain blood glucose levels ies investigating consumption of a range enhance performance have ranged and improve performance (106). of macronutrient composition during the from approximately 200 to 300 g car- For longer events, consuming 0.7 g training period on athletic performance bohydrate for meals consumed 3 to 4 carbohydrate/kg body weight per hour were evaluated. Nine studies have re- hours before exercise. Studies report (approximately 30 to 60 g per hour) has ported that the consumption of a high either no effect or beneficial effects of been shown unequivocally to extend carbohydrate diet ( 60% of energy) dur- pre-event feeding on performance (91- endurance performance (107,108). ing the training period and the week be- 98). Data are equivocal concerning Consuming carbohydrates during ex- March 2009 ● Journal of the AMERICAN DIETETIC ASSOCIATION 519
  12. 12. ercise is even more important in situ- will finish a marathon with depleted repair and promote a more anabolic ations when athletes have not carbo- glycogen stores, whereas glycogen hormonal profile (33). hydrate-loaded, not consumed pre- depletion would be less marked fol- Conclusion Statement. Twenty-five studies exercise meals, or restricted energy lowing a 90-minute training run. Be- investigating the consumption of a range intake for weight loss. Carbohydrate cause athletes competing in a mara- of macronutrient composition during the intake should begin shortly after the thon are not likely to perform another recovery period were evaluated. Nine onset of activity; consuming a given race or hard workout the same day, studies report that consumption of diets amount of carbohydrate as a bolus the timing and composition of the higher in carbohydrate ( 65% carbohy- after 2 hours of exercise is not as postexercise meal is less critical for drate or 0.8 to 1.0 g carbohydrate/kg body effective as consuming the same these athletes. Conversely, a triath- weight/hour) during the recovery period amount at 15 to 20 minute intervals lete participating in a 90-minute run increase plasma glucose and insulin con- throughout the 2 hours of activity in the morning and a 3-hour cycling centrations and increase muscle glyco- (109). The carbohydrate consumed workout in the afternoon needs to gen resynthesis. Provided that carbohy- should yield primarily glucose; fruc- maximize recovery between training drate intake is sufficient, four studies tose alone is not as effective and may sessions. The post workout meal as- show no significant benefit of addi- cause diarrhea, although mixtures of sumes considerable importance in tional protein intake and two studies glucose and fructose, other simple meeting this goal. show no significant effect of meal timing sugars and maltodextrins, appear ef- Timing of post-exercise carbohy- on muscle glycogen resynthesis during fective (107). If the same total amount drate intake affects glycogen synthe- the recovery period. Studies focusing on of carbohydrate and fluid is ingested, sis over the short term (110). Con- carbohydrate consumption during recov- the form of carbohydrate does not sumption of carbohydrates within 30 ery periods of 4 hours or more suggest seem to matter. Some athletes may minutes after exercise (1.0 to 1.5 g improvements in athletic performance. prefer to use a sport drink whereas carbohydrate/kg at 2-hour intervals Evidence Grade II Fair (www. others may prefer to consume a car- up to 6 hours is often recommended) bohydrate snack or sports gel and results in higher glycogen levels post conclusion_statement_id 250451). consume water. As described else- exercise than when ingestion is de- where in this document, adequate layed for 2 hours (111). It is unneces- fluid intake is also essential for main- sary for athletes who rest one or more DIETARY SUPPLEMENTS AND ERGOGENIC taining endurance performance. days between intense training ses- AIDS Conclusion Statement. Thirty-six studies sions to practice nutrient timing The overwhelming number and in- investigating the consumption of a range with regard to glycogen replenish- creased availability of sports supple- of macronutrient composition during ment provided sufficient carbohy- ments presents an ongoing challenge competition on athletic performance drates are consumed during the 24- for the practitioner and the athlete to were evaluated. Seven studies based on hour period subsequent to the exercise keep up-to-date about the validity of carbohydrate consumption during exer- bout (112). Nevertheless, consuming a both the claims and scientific evidence. cise lasting less than 60 minutes show meal or snack in close proximity to the Although dietary supplements, as well conflicting results on athletic perfor- end of exercise may be important for nutritional ergogenic aids—nutritional mance. However, of 17 studies based on athletes to meet daily carbohydrate products that enhance performance— carbohydrate consumption during exer- and energy goals. are highly prevalent, the fact remains cise lasting greater than 60 minutes, five The type of carbohydrate consumed that very few improve performance reported improved metabolic response, also affects post-exercise glycogen syn- (117-119) and some may cause concern. and seven of 12 studies reported im- thesis. When comparing simple sugars, In the United States, the Dietary provements in athletic performance. Ev- glucose and sucrose appear equally ef- Supplements and Health Education idence is inconclusive regarding the ad- fective when consumed at a rate of 1.0 Act of 1994 allows supplement man- dition of protein to carbohydrate during to 1.5 g/kg body weight for 2 hours; ufacturers to make health claims re- exercise on athletic performance. Seven fructose alone is less effective (113). garding the effect of products on body studies based on consumption of pre- With regard to whole foods, consump- structure or function, but not thera- exercise meals in addition to carbohy- tion of carbohydrate with a high glyce- peutic claims to “diagnose, mitigate, drate consumption during exercise sug- mic index results in higher muscle gly- treat, cure, or prevent” a specific dis- gest enhanced athletic performance. cogen levels 24 hours after glycogen- ease or medical condition (117,120). Evidence Grade II Fair (www. depleting exercise as compared with As long as a special supplement label the same amount of carbohydrates pro- indicates the active ingredients and conclusion_statement_id 250453). vided as foods with a low glycemic in- the entire ingredients list is provided, dex (114). Application of these findings claims for enhanced performance can must be considered in conjunction with be made, valid or not. The Act, how- Recovery the athlete’s overall diet. When isoca- ever, made the US Food and Drug The timing and composition of the loric amounts of carbohydrates or car- Administration responsible for evalu- post competition or postexercise meal bohydrates plus protein and fat are ating and enforcing safety. In 2003, or snack depend on the length and provided following endurance (115) or the Food and Drug Administration intensity of the exercise session (eg, resistance exercise (116), glycogen syn- Task Force on Consumer Health In- whether glycogen depletion occurred), thesis rates are similar. Including pro- formation for Better Nutrition pro- and when the next intense workout tein in a postexercise meal may provide posed a new system for evaluating will occur. For example, most athletes needed amino acids for muscle protein health claims that uses an evidence- 520 March 2009 Volume 109 Number 3