Position of the Academy of Nutrition and Dietetics ... › attachments › document › a...athletic performance and emerging trends in the ﬁeld of sports nutrition. Athletes should

This article is being published concur-rently on the Dietitians of Canadawebsite (www.dietitians.ca/sports) andin Medicine & Science in Sports andExercise�. The articles are identicalexcept for minor stylistic and spellingdifferences in keeping with each jour-nal’s style. Either citation can be usedwhen citing this article.

2212-2672/Copyright ª 2016 by theAcademy of Nutrition and Dietetics,American College of Sports Medicine, andDietitians of Canada.http://dx.doi.org/10.1016/j.jand.2015.12.006

*Because credentialing practices varyinternationally, the term “sports dieti-tian”will be used throughout this articleto encompass all terms of accreditation,including registered dietitian nutritionist(RDN), registered dietitian (RD), profes-sional dietitian (PDt), or Board CertifiedSpecialist in Sports Dietetics (CSSD).

ª 2016 by the Academy of Nutrition and Dietetics, American College ofSports Medicine, and Dietitians of Canada. J

FROM THE ACADEMY

Position Paper

Position of the Academy of Nutrition andDietetics, Dietitians of Canada, and theAmerican College of Sports Medicine: Nutritionand Athletic Performance

ABSTRACTIt is the position of the Academy of Nutrition and Dietetics (Academy), Dietitians ofCanada (DC), and the American College of Sports Medicine (ACSM) that the performanceof, and recovery from, sporting activities are enhanced by well-chosen nutrition stra-tegies. These organizations provide guidelines for the appropriate type, amount, andtiming of intake of food, fluids, and supplements to promote optimal health and per-formance across different scenarios of training and competitive sport. This positionpaper was prepared for members of the Academy, DC, and ACSM, other professionalassociations, government agencies, industry, and the public. It outlines the Academy’s,DC’s, and ACSM’s stance on nutrition factors that have been determined to influenceathletic performance and emerging trends in the field of sports nutrition. Athletesshould be referred to a registered dietitian nutritionist for a personalized nutrition plan.In the United States and in Canada, the Certified Specialist in Sports Dietetics is aregistered dietitian nutritionist and a credentialed sports nutrition expert.J Acad Nutr Diet. 2016;116:501-528.

POSITION STATEMENT

It is the position of the Academy of Nutritionand Dietetics, Dietitians of Canada, and theAmerican College of Sports Medicine that theperformance of, and recovery from, sportingactivities are enhanced by well-chosen nutri-tion strategies. These organizations provideguidelines for the appropriate type, amount,and timing of intake of food, fluids, and di-etary supplements to promote optimal healthand sport performance across different sce-narios of training and competitive sport.

OURNAL OF THE AC

HIS ARTICLE OUTLINES THE to accommodate the unique issues of This Academy position paper includes the

authors’ independent review of the litera-ture in addition to systematic review con-ducted using the Academy’s EvidenceAnalysis Process and information from theAcademy Evidence Analysis Library (EAL).Topics from the EAL are clearly delineated.

Tcurrent energy, nutrient, andfluid recommendations foractive adults and competitiveathletes. These general recommenda-tions can be adjusted by sports dietitians*

The use of an evidence-based approachprovides important added benefits toearlier review methods. The major advan-tage of the approach is the more rigorousstandardization of review criteria, whichminimizes the likelihood of reviewer biasand increases the easewithwhichdisparatearticles may be compared. For a detaileddescription of the methods used in the ev-idence analysis process, access the Aca-demy’s Evidence Analysis Process (http:www.andevidencelibrary.com/eaprocess).

Conclusion Statements are assigned agrade by an expert work group based onthe systematic analysis and evaluation ofthe supporting research evidence. GradeI¼Good; Grade II¼Fair; Grade III¼Limited;Grade IV Expert Opinion Only; and GradeV¼Not Assignable (because there is no ev-idence to support or refute the conclusion).

See grade definitions at www.andevidencelibrary.com/.

Evidence-based information for this andother topics can be found at https://www.andevidencelibrary.com and subscriptionsfor nonmembers are purchasable at https://www.andevidencelibrary.com/store.cfm.

individual athletes regarding health,nutrient needs, performance goals,physique characteristics (ie, body size,shape, growth, and composition), prac-tical challenges, and food preferences.

EVIDENCE-BASED ANALYSISThis article was developed using theAcademy of Nutrition and Dietetics(Academy) Evidence Analysis Library(EAL) andwill outline some key themesrelated to nutrition and athletic per-formance. The EAL is a synthesis ofrelevant nutrition research on impor-tant dietetics-related practice ques-tions. The publication range for theevidence-based analysis spannedMarch 2006 to November 2014. For thedetails on the systematic review andmethodology go to www.andevidencelibrary.com. Figure 1 presents the evi-dence analysis questions used in thisposition paper.

NEW PERSPECTIVES IN SPORTSNUTRITIONThe past decade has seen an increase inthe number and topics of publications

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http://www.andevidencelibrary.comhttp://www.andevidencelibrary.comhttp://www.andevidencelibrary.com/eaprocesshttp://www.andevidencelibrary.com/eaprocesshttp://www.andevidencelibrary.com/http://www.andevidencelibrary.com/https://www.andevidencelibrary.comhttps://www.andevidencelibrary.comhttps://www.andevidencelibrary.com/store.cfmhttps://www.andevidencelibrary.com/store.cfmhttp://crossmark.crossref.org/dialog/?doi=10.1016/j.jand.2015.12.006&domain=pdfhttp://www.dietitians.ca/sportshttp://dx.doi.org/10.1016/j.jand.2015.12.006

Evidence Analysis Library question Conclusion and evidence grade

Energy balance and body composition

#1: In adult athletes, what effect doesnegative energy balance have on exerciseperformance?

In three out of six studies of male and female athletes, negative energybalance (losses of 0.02% to 5.8% body mass; over five 30-day periods) wasnot associated with decreased performance. In the remaining three studieswhere decrements in both anaerobic and aerobic performance wereobserved, slow rates of weight loss (0.7% reduction body mass) were morebeneficial to performance compared to fast (1.4% reduction body mass)and one study showed that self-selected energy restriction resulted indecreased hormone levels.Grade II - Fair

#2: In adult athletes, what is the time, energy,and macronutrient requirement to gain leanbody mass?

Over periods of 4-12 weeks, increasing protein intake during hypocaloricconditions maintains lean body mass in male and female resistance-trainedathletes. When adequate energy is provided or weight loss is gradual, anincrease in lean body mass may be observedGrade III - limited

Recovery

#3: In adult athletes, what is the effect ofconsuming carbohydrate on carbohydrateand protein-specific metabolic responses and/or exercise performance during recovery?

Based on the limited evidence available, there were no clear effects ofcarbohydrate supplementation during and after endurance exercise oncarbohydrate and protein-specific metabolic responses during recovery.Grade III - Limited

#4: What is the effect of consumingcarbohydrate on exercise performance duringrecovery?

Based on the limited evidence available, there were no clear effects ofcarbohydrate supplementation during and after endurance exercise onendurance performance in adult athletes during recovery.Grade III - Limited

#5: In adult athletes, what is the effect ofconsuming carbohydrate and proteintogether on carbohydrate- and protein-specific metabolic responses during recovery?

� Compared to ingestion of carbohydrate alone, coingestion of car-bohydrate plus protein together during the recovery period resultedin no difference in the rate of muscle glycogen synthesis.

� Coingestion of protein with carbohydrate during the recovery periodresulted in improved net protein balance postexercise.

� The effect of coingestion of protein with carbohydrate on creatinekinase levels is inconclusive and shows no impact on muscle sore-ness postexercise.

� Grade I - Good#6: In adult athletes, what is the effect ofconsuming carbohydrate and proteintogether on carbohydrate and protein-specificmetabolic responses during recovery?

Coingestion of carbohydrate plus protein, together during the recoveryperiod, resulted in no clear influence on subsequent strength or sprintpower.Grade II - Fair

#7: In adult athletes, what is the effect ofconsuming carbohydrate and proteintogether on exercise performance duringrecovery?

Ingesting protein during the recovery period (postexercise) led toaccelerated recovery of static force and dynamic power production duringthe delayed onset muscle soreness period and more repetitions performedsubsequent to intense resistance training.Grade II - Fair

(continued on next page)

Figure 1. Evidence analysis questions included in the position statement. Evidence grades: Grade I: Good, Grade II: Fair, Grade III:Limited, Grade IV: Expert opinion only; and Grade V: Not assignable. Refer to http://www.andevidencelibrary.com/ for a complete listof evidence analysis citations.

FROM THE ACADEMY

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Evidence Analysis Library question Conclusion and evidence grade

Energy balance and body composition

#8: In adult athletes, what is the effect ofconsuming protein on carbohydrate- andprotein-specific metabolic responses duringrecovery?

Ingesting protein (approximately 20 to 30 g total protein, or approximately10 g essential amino acids) during exercise or the recovery period(postexercise) led to increased whole body and muscle protein synthesis aswell as improved nitrogen balance.Grade I- Good

Training

#9: In adult athletes, what is the optimal blendof carbohydrates for maximal carbohydrateoxidation during exercise?

Based on the limited evidence available, carbohydrate oxidation wasgreater in carbohydrate conditions (glucose and glucoseþfructose)compared with water placebo, but no differences between the twocarbohydrate blends tested were observed in male cyclists. Exogenouscarbohydrate oxidation was greater in the glucoseþfructose condition vsglucose-only in a single study.Grade III - Limited

#10: In adult athletes, what effect doestraining with limited carbohydrate availabilityhave on metabolic adaptations that lead toperformance improvements?

Training with limited carbohydrate availability may lead to some metabolicadaptations during training, but did not lead to performanceimprovements. Based on the evidence examined, whereas there isinsufficient evidence supporting a clear performance effect, training withlimited carbohydrate availability impaired training intensity and duration.Grade II - Fair

#11: In adult athletes, what effect doesconsuming high or low glycemic meals orfoods have on training-related metabolicresponses and exercise performance?

In the majority of studies examined, neither glycemic index nor glycemicload affected endurance performance nor metabolic responses whenconditions were matched for carbohydrate and energy.Grade I - Good

Figure 1. (continued) Evidence analysis questions included in the position statement. Evidence grades: Grade I: Good, Grade II: Fair,Grade III: Limited, Grade IV: Expert opinion only; and Grade V: Not assignable. Refer to http://www.andevidencelibrary.com/ for acomplete list of evidence analysis citations.

FROM THE ACADEMY

of original research and review,consensus statements from sportingorganizations, and opportunities forqualification and accreditation relatedto sports nutrition and dietetics. Thisbears witness to sports nutrition as adynamic area of science and practicethat continues to flourish in boththe scope of support it offers to ath-letes and the strength of evidencethat underpins its guidelines. Beforeembarking on a discussion of individ-ual topics, it is valuable to identify arange of themes in contemporarysports nutrition that corroborate andunify the recommendations in thisarticle.

1. Nutrition goals and require-ments are not static. Athletesundertake a periodized pro-gram in which preparation forpeak performance in targetedevents is achieved by inte-grating different types of

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workouts in the various cyclesof the training calendar. Nutri-tion support also needs to beperiodized, taking into accountthe needs of daily training ses-sions (which can range fromminor in the case of “easy”workouts to substantial in thecase of high-quality sessions(eg, high-intensity, strenuous,or highly skilled workouts) andoverall nutritional goals.

2. Nutrition plans need to bepersonalized to the individualathlete to take into account thespecificity and uniqueness ofthe event, performance goals,practical challenges, food pref-erences, and responses tovarious strategies.

3. A key goal of training is toadapt the body to developmetabolic efficiency and flexi-bility, whereas competitionnutrition strategies focus on

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providing adequate substratestores to meet the fuel de-mands of the event and sup-port cognitive function.

4. Energy availability, which con-siders energy intake in relationto the energy cost of exercise,sets an important foundationfor health and the success ofsports nutrition strategies.

5. The achievement of the bodycomposition associated withoptimal performance is nowrecognized as an important butchallenging goal that needs tobe individualized and perio-dized. Care should be taken topreserve health and long-termperformance by avoiding prac-tices that create unacceptablylow energy availability andpsychological stress.

6. Training and nutrition have astrong interaction in accli-mating the body to develop

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FROM THE ACADEMY

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functional and metabolic ad-aptations. Although optimalperformance is underpinnedby the provision of proactivenutrition support, training ad-aptations may be enhanced inthe absence of such support.

7. Some nutrients (eg, energy,carbohydrate, and protein)should be expressed usingguidelines per kilogram bodymass to allow recommenda-tions to be scaled to the largerange in the body sizes of ath-letes. Sports nutrition guide-lines should also consider theimportance of the timing ofnutrient intake and nutritionalsupport over the day and inrelation to sport rather thangeneral daily targets.

8. Highly trained athletes walk atightrope between traininghard enough to achieve amaximal training stimulus andavoiding the illness and injuryrisk associated with an exces-sive training volume.

9. Competition nutrition shouldtarget specific strategies thatreduce or delay factors thatwould otherwise cause fatiguein an event; these are specificto the event, the environ-ment/scenario in which it isundertaken, and the individ-ual athlete.

10. New performance nutritionoptions have emerged in thelight of developing but robustevidence that brain sensing ofthe presence of carbohydrate,and potentially other nutri-tional components, in the oralcavity can enhance perceptionsof well-being and increase self-chosen work rates. Such find-ings present opportunities forintake during shorter events, inwhich fluid or food intake waspreviously not considered tooffer a metabolic advantage, byenhancing performance via acentral effect.

11. A pragmatic approach to adviceregarding the use of supple-ments and sports foods isneeded in the face of the highprevalence of interest in, anduse by, athletes and the evi-dence that some products canusefully contribute to a sports

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nutrition plan and/or directlyenhance performance. Athletesshould be assisted to undertakea cost-to-benefit analysis of theuse of such products and torecognize that they are of thegreatest value when added to awell-chosen eating plan.

THEME 1: NUTRITION FORATHLETE PREPARATIONEnergy Requirements, EnergyBalance, and Energy AvailabilityAn appropriate energy intake is thecornerstone of the athlete’s diet becauseit supports optimal body function, de-termines the capacity for intake ofmacronutrient and micronutrients, andassists in manipulating body composi-tion. An athlete’s energy intake fromfood, fluids, and supplements can bederived from weighed/measured foodrecords (typically 3 to 7 days), a multi-pass 24-hour recall, or from foodfrequency questionnaires.1 There areinherent limitations with all of thesemethods, with a bias to the under-reportingof intakes. Extensive educationregarding the purpose and protocols ofdocumenting intakes may assist withcompliance and enhance the accuracyandvalidityof self-reported information.Meanwhile, an athlete’s energy re-

quirements depend on the periodizedtraining and competition cycle, and willvary from day to day throughout theyearly training plan relative to changesin training volume and intensity. Factorsthat increase energy needs abovenormal baseline levels include exposureto cold or heat, fear, stress, high altitudeexposure, some physical injuries, spe-cific drugs or medications (eg, caffeineand nicotine), increases in fat-free mass(FFM), and possibly the luteal phase ofthe menstrual cycle.2 Aside from re-ductions in training, energy re-quirements are lowered by aging,decreases in FFM, and possibly thefollicular phase of the menstrual cycle.3

Energy balance occurs when totalenergy intake (EI) equals total energyexpenditure (TEE), which in turn con-sists of the summation of basal meta-bolic rate (BMR), the thermic effect offood (TEF), and the thermic effect ofactivity (TEA).TEE[BMRDTEFDTEATEA[Planned Exercise Expendi-

tureDSpontaneous Physical ActivityDNonexercise Activity Thermogenesis

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Techniques used to measure or esti-mate components of TEE in sedentaryand moderately active populations canalso be applied to athletes, but there aresome limitations to this approach,particularly in highly competitive ath-letes. Because the measurement of BMRrequires subjects to remainexclusivelyatrest, it is more practical to measurerestingmetabolic rate (RMR),whichmaybe 10% higher. Although population-specific regression equations areencouraged, a reasonable estimate ofBMR can be obtained using either theCunningham4 or the Harris-Benedict5

equations, with an appropriate activityfactor being applied to estimate TEE.Whereas RMR represents 60% to 80% ofTEE for sedentary individuals, it may beas little as 38% to 47% of TEE for eliteendurance athletes whomay have a TEAas high as 50% of TEE.2

TEA includes planned exerciseexpenditure, spontaneous physical ac-tivity (eg, fidgeting), and nonexerciseactivity thermogenesis. Energy expen-diture from exercise can be estimatedin several ways from activity logs(1 to 7 days’ duration) with subjectiveestimates of exercise intensity usingactivity codes and metabolic equiva-lents,6,7 US Dietary Guidelines, 2015,8

and the Dietary Reference Intakes(DRIs).9 The latter two typically un-derestimate the requirements of ath-letes because they fail to cover therange in body size or activity levels ofcompetitive populations. Energy avail-ability (EA) is a concept of recent cur-rency in sports nutrition, whichequates energy intake with re-quirements for optimal health andfunction rather than energy balance.EA, defined as dietary intake minusexercise energy expenditure normal-ized to FFM, is the amount of energyavailable to the body to perform allother functions after the cost of exer-cise is subtracted.10 The concept wasfirst studied in women, where an EA of45 kcal/kg FFM/day was found to beassociated with energy balance andoptimal health; meanwhile, a chronicreduction in EA, (particularly below 30kcal/kg FFM/day) was associated withimpairments of a variety of bodyfunctions.10 Low EA may occur frominsufficient EI, high TEE, or a combi-nation of the two. It may be associatedwith disordered eating, a misguided orexcessively rapid program for loss ofbody mass, or inadvertent failure to


FROM THE ACADEMY

meet energy requirements during aperiod of high-volume training orcompetition.10

Example Calculation of EA60 kg body weight (BW), 20% body

fat, 80% FFM (¼48.0 kg FFM), EI¼2,400kcal/day, additional energy expendi-ture from exercise¼500 kcal/dayEA¼(EIeEEE)/FFM¼(2,400e500)

kcal$d/48.0 kg¼39.6 kcal/kg FFM/dayThe concept of EA emerged from the

study of the female athlete triad (Triad),which started as a recognition of theinterrelatedness of clinical issues withdisordered eating, menstrual dysfunc-tion, and low bone mineral density infemale athletes and then evolved into abroader understanding of the concernsassociated with any movement alongthe spectra away from optimal energyavailability, menstrual status, and bonehealth.11 Although not embedded in theTriad spectrum, it is recognized thatother physiological consequences mayresult from one of the components ofthe Triad in female athletes, such asendocrine, gastrointestinal, renal,neuropsychiatric, musculoskeletal, andcardiovascular dysfunction.11 Indeed, anextension of the Triad has been pro-posed—the Relative Energy Deficiencyin Sport (RED-S)—as an inclusivedescription of the entire cluster ofphysiologic complications observed inmale and female athletes who consumeenergy intakes that are insufficient inmeeting the needs for optimal bodyfunction once the energy cost of exercisehas been removed.12 Specifically, healthconsequences of RED-S may negativelyaffect menstrual function; bone health;and endocrine, metabolic, hematologi-cal, growth and development, psycho-logical, cardiovascular, gastrointestinal,and immunological systems. Potentialperformance effects of RED-S mayinclude decreased endurance, increasedinjury risk, decreased training response,impaired judgment, decreased coordi-nation, decreased concentration, irrita-bility, depression, decreased glycogenstores, and decreased muscle strength.12

It is now also recognized that impair-ments of health and function occuracross the continuum of reductions inEA, rather than occurring uniformly atan EA threshold, and require furtherresearch.12 It should be appreciated thatlow EA is not synonymous with negativeenergy balance or weight loss; indeed, ifa reduction in EA is associated with areduction in RMR, it may produce a new


steady-state of energy balance or weightstability at a lowered energy intake thatis insufficient to provide for healthybody function.Regardless of the terminology, it is

apparent that low EA in male and fe-male athletes may compromiseathletic performance in the short andlong-term. Screening and treatmentguidelines have been established formanagement of low EA11,12 and shouldinclude assessment with the EatingDisorder Inventory-3 resource13 or theDiagnostic and Statistical Manual ofMental Disorders, fifth edition, whichincludes changes in eating disordercriteria.14 There is evidence that in-terventions to increase EA are suc-cessful in reversing at least someimpaired body functions; for example,in a 6-month trial with female athletesexperiencing menstrual dysfunction,dietary treatment to increase EA tow40 kcal/kg FFM/day resulted inresumption of menses in all subjects ina mean of 2.6 months.6

Body Composition and SportsPerformanceVarious attributes of physique (bodysize, shape, and composition) areconsidered to contribute to success invarious sports. Of these, body mass(“weight”) and body composition areoften focal points for athletes becausethey are most able to be manipulated.Although it is clear that the assessmentand manipulation of body compositionmay assist in the progression of anathletic career, athletes, coaches, andtrainers should be reminded that ath-letic performance cannot be accuratelypredicted solely based on BW andcomposition. A single and rigid optimalbody composition should not be rec-ommended for any event or group ofathletes.15 Nevertheless, there are re-lationships between body compositionand sports performance that areimportant to consider within an ath-lete’s preparation.In sports involving strength and po-

wer, athletes strive to gain FFM via aprogram of muscle hypertrophy atspecified times of the annual macro-cycle. Whereas some athletes aim togain absolute size and strength per se,in other sports, in which the athletemust move their own body mass orcompete within weight divisions, it isimportant to optimize power to weightratios rather than absolute power.16

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Thus, some power athletes also desireto achieve low body fat levels. Insports involving weight divisions (eg,combat sports, lightweight rowing, andweightlifting), competitors typicallytarget the lowest achievable BW cate-gory while maximizing their leanmass within this target.

Other athletes strive to maintain alow body mass and/or body fat level forseparate advantages.17 Distance run-ners and cyclists benefit from a lowenergy cost of movement and a favor-able ratio of weight to surface area forheat dissipation. Team athletes can in-crease their speed and agility by beinglean, whereas athletes in acrobaticsports (eg, diving, gymnastics, anddance) gain biomechanical advantagesin being able to move their bodieswithin a smaller space. In some ofthese sports and others (eg, bodybuilding), there is an element of aes-thetics in determining performanceoutcomes. Although there are demon-strated advantages to achieving acertain body composition, athletes mayfeel pressure to strive to achieve unre-alistically low targets of weight/bodyfat or to reach them in an unrealistictime frame.15 Such athletes may besusceptible to practicing extremeweight control behaviors or continuousdieting, exposing themselves tochronic periods of low EA and poornutrient support in an effort to repeatprevious success at a lower weight orleaner body composition.15,18 Extrememethods of weight control can bedetrimental to health and perfor-mance, and disordered eating patternshave also been observed in these sportscenarios.15,18

Nevertheless, there are scenarios inwhich an athlete will enhance his orher health and performance byreducing BW or body fat as part of aperiodized strategy. Ideally, this occurswithin a program that gradually ach-ieves an individualized optimal bodycomposition over the athlete’s athleticcareer, and allows weight and body fatto track within a suitable range withinthe annual training cycle.18 The pro-gram should also include avoiding sit-uations in which athletes inadvertentlygain excessive amounts of body fat as aresult of a sudden energy mismatchwhen energy expenditure is abruptlyreduced (eg, the off-season or injury).In addition, athletes are warned againstthe sudden or excessive gain in body

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FROM THE ACADEMY

fat that is part of the culture of somesports where a high body mass isdeemed useful for performance.Although body mass index is notappropriate as a body compositionsurrogate in athletes, a chronic interestin gaining weight may put some ath-letes at risk for an obese body massindex, which may increase the risk ofmeeting the criteria for metabolicsyndrome.19 Sports dietitians should beaware of sports that promote theattainment of a large body mass andscreen for metabolic risk factors.19

Methodologies for Body Composi-tion Assessment. Techniques used toassess athlete body compositioninclude dual energy x-ray absorptiom-etry (DXA), hydrodensitometry, airdisplacement plethysmography, skin-fold measurements, and single andmultifrequency bioelectrical imped-ance analysis. Although DXA is quickand noninvasive, issues around cost,accessibility, and exposure to a smallradiation dose limit its utility, par-ticularly for certain populations.20

When undertaken according to stan-dardized protocols, DXA has the loweststandard error of estimate, whereasskinfold measures have the highest; airdisplacement plethysmography (Bod-Pod, Life Measurement, Inc) providesan alternative method that is quick andreliable, but may underestimate bodyfat by 2% to 3%.20 Skinfold measure-ment and other anthropometric dataserve as an excellent surrogate mea-sure of adiposity and muscularity whenprofiling composition changes inresponse to training interventions.20

However, it should be noted that thestandardization of skinfold sites, mea-surement techniques, and calipers varyaround the world. Despite some limi-tations, this technique remains a pop-ular method of choice due toconvenience and cost, with informa-tion being provided in absolute mea-sures and compared with sequentialdata from the individual athlete or, in ageneral way, with normative datacollected in the same way from athletepopulations.20,21

All body composition assessmenttechniques should be scrutinized toensure accuracy and reliability. Testingshould be conducted with the samecalibrated equipment, with a stan-dardized protocol, and by technicians


with known testeretest reliability.Where population-specific predictionequations are used, they should becross-validated and reliable. Athletesshould be educated on the limitationsassociated with body compositionassessment and should strictly followpreassessment protocols. These in-structions, which include maintaininga consistent training volume, fastingstatus, and hydration from test totest20 should be enforced to avoidcompromising the accuracy and reli-ability of body composition measures.Body composition should be deter-

mined within a sports program ac-cording to a schedule that isappropriate to the performance of theevent, the practicality of undertakingassessments, and the sensitivity of theathlete. There are technical errorsassociated with all body compositiontechniques that limit the usefulness ofmeasurement for athlete selection andperformance prediction. In lieu ofsetting absolute body compositiongoals or applying absolute criteria tocategorize groups of athletes, it ispreferred that normative data are pro-vided in terms of ranges.21 Becausebody fat content for an individualathlete will vary over the season andover the athlete’s career, goals for bodycomposition should be set in terms ofranges that can be appropriatelytracked at critical times. When con-ducting such monitoring programs, it isimportant that the communication ofresults with coaches, training staff, andathletes is undertaken with sensitivity,that limitations in measurement tech-nique are recognized, and that care istaken to avoid promoting an unhealthyobsession with body composition.17,18

Sports dietitians have important op-portunities to work with these athletesto help promote a healthy bodycomposition, and to minimize theirreliance on rapid-weight loss tech-niques and other hazardous practicesthat may result in performance decre-ments, loss of FFM, and chronic healthrisks. Many themes should beaddressed and include the creation of aculture and environment that valuessafe and long-term approaches tomanagement of body composition;modification of rules or practicesaround selection and qualification forweight classes;16,19,22 and programsthat identify disordered eating

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practices at an early stage for inter-vention, and where necessary, removalfrom play.18

Principles of Altering Body Com-position and Weight. Athletes oftenneed assistance in setting appropriateshort-term and long-term goals, un-derstanding nutrition practices thatcan safely and effectively increasemuscle mass or reduce body fat/weight, and integrating these strategiesinto an eating plan that achieves otherperformance nutrition goals. Frequentfollow up with these athletes may havelong-term benefits, including shep-herding the athlete through short-termgoals and reducing reliance on extremetechniques and fad diets/behaviors.

There is ample evidence in weightsensitive and weight-making sportsthat athletes frequently undertakerapid weight loss strategies to gain acompetitive advantage.20,23,24 Howev-er, the resultant hypohydration (bodywater deficit), loss of glycogen storesand lean mass, and other outcomes ofpathologic behaviors (eg, purging,excessive training, or starving) canimpair health and performance.18

Nevertheless, responsible use of short-term, rapid weight-loss techniques,when indicated, is preferred overextreme and extended energy restric-tion and suboptimal nutrition sup-port.17 When actual loss of BW isrequired, it should be programmed tooccur in the base phase of training orwell out from competition to minimizeloss of performance,25 and should beachieved with techniques that maxi-mize loss of body fat while preservingmuscle mass and other health goals.Such strategies include achieving aslight energy deficit to achieve a slowrather than rapid rate of loss andincreasing dietary protein intake. Inthis regard, the provision of a higherprotein intake (2.3 vs 1 g/kg/day) in ashorter-term (2 week), energy-restricted diet in athletes was foundto retain muscle mass while losingweight and body fat.26 Furthermore,FFM and performance may be betterpreserved in athletes who minimizeweekly weight loss to

FROM THE ACADEMY

Nevertheless, for most athletes, thepractical approach of decreasing en-ergy intake by w250 to 500 kcal/dayfrom their periodized energy needs,while either maintaining or slightlyincreasing energy expenditure, canachieve progress toward short-termbody composition goals over approxi-mately 3 to 6 weeks. In some situa-tions, additional moderate aerobictraining and close monitoring can beuseful.27 These strategies can beimplemented to help augment thediet-induced energy deficits withoutnegatively impacting recovery fromsport-specific training. Arranging thetiming and content of meals to sup-port training nutrition goals and re-covery may reduce fatigue duringfrequent training sessions and mayhelp optimize body composition overtime.18 Overall barriers to bodycomposition management includelimited access to healthy food options,limited skills or opportunity for foodpreparation, lack of daily routine, andexposure to catering featuring unlim-ited portion sizes and energy-densefoods. Such factors, particularly foundin association with the travel andcommunal living experiences in theathlete lifestyle, can promote poordietary quality that thwarts progressand may lead to the pursuit of quickfixes, acute dieting, and extremeweight loss practices.EAL Question #1 (Figure 1) exam-

ined the effect of negative energy bal-ance on sport performance, findingonly fair support for an impairment ofphysical capacity due to a hypo-energetic diet in the currently exam-ined scenarios. However, few studieshave investigated the overlay of factorscommonly seen in practice, includingthe interaction of poor dietary quality,low carbohydrate availability, exces-sive training, and acute dehydration onchronic energy restriction. The chal-lenge of detecting small but importantchanges in sports performance isnoted in all areas of sports nutrition.28

EAL Question #2 summarizes theliterature on optimal timing, energy,and macronutrient characteristics of aprogram supporting a gain in FFMwhen in energy deficit (Figure 1).Again the literature is limited inquantity and range to allow definitiverecommendations to be made,although there is support for the ben-efits of increased protein intake.


Nutrient Requirements for SportEnergy Pathways and TrainingAdaptations. Guidelines for thetiming and amount of intake of mac-ronutrients in an athlete’s diet shouldbe underpinned by a fundamental un-derstanding of how training-nutrientinteractions affect energy systems,substrate availability, and training ad-aptations. Exercise is fueled by an in-tegrated series of energy systems thatinclude nonoxidative (phosphagen andglycolytic) and aerobic (fat and carbo-hydrate oxidation) pathways, usingsubstrates that are both endogenousand exogenous in origin. ATP andphosphocreatine (phosphagen system)provide a rapidly available energysource for muscular contraction, butnot at sufficient levels to provide acontinuous supply of energy for longerthan w10 seconds. The anaerobicglycolytic pathway rapidly metabolizesglucose and muscle glycogen throughthe glycolytic cascade and is the pri-mary pathway supporting high-intensity exercise lasting 10 to 180seconds. Because neither the phospha-gen nor the glycolytic pathway cansustain energy demands to allow mus-cles to contract at a very high rate forlonger lasting events, oxidative path-ways provide the primary fuels forevents lasting longer than w2 minutes.The major substrates include muscleand liver glycogen, intramuscular lipid,adipose tissue triglycerides, andamino acids from muscle, blood, liver,and the gut. As oxygen becomes moreavailable to the working muscle, thebody uses more of the aerobic (oxida-tive) pathways and less of the anaer-obic (phosphagen and glycolytic)pathways. The greater dependenceupon aerobic pathways does notoccur abruptly, nor is one pathway everrelied on exclusively. The intensity,duration, frequency, type of training,sex, and training level of the individual,as well as prior nutrient intake andsubstrate availability, determine therelative contribution of energy path-ways and when crossover betweenpathways occurs. For a more completeunderstanding of fuel systems forexercise, the reader is directed to spe-cific texts.29

An athlete’s skeletal muscle has aremarkable plasticity to respondquickly to mechanical loading andnutrient availability resulting in

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condition-specific metabolic and func-tional adaptations.30 These adaptationsinfluence performance nutrition rec-ommendations with the overarchinggoals that energy systems should betrained to provide the most economicalsupport for the fuel demands of anevent while other strategies shouldachieve appropriate substrate avail-ability during the event itself. Adapta-tions that enhance metabolic flexibilityinclude increases in transport mole-cules that carry nutrients acrossmembranes or to the site of their usewithin the muscle cell, increases inenzymes that activate or regulatemetabolic pathways, enhancement ofthe ability to tolerate the side-productsof metabolism, and an increase in thesize of muscle fuel stores.3 Althoughsome muscle substrates (eg, body fat)are present in relatively large quanti-ties, others may need to be manipu-lated according to specific needs (eg,carbohydrate supplementation toreplace muscle glycogen stores).

Carbohydrate. Carbohydrate hasrightfully received a great deal ofattention in sports nutrition due to anumber of special features of its rolein the performance of, and adaptationto training. First, the size of body car-bohydrate stores is relatively limitedand can be acutely manipulated on adaily basis by dietary intake or even asingle session of exercise.3 Second,carbohydrate provides a key fuel forthe brain and central nervous systemand a versatile substrate for muscularwork where it can support exerciseover a large range of intensities due toits use by both anaerobic and oxida-tive pathways. Even when working atthe highest intensities that can besupported by oxidative phosphoryla-tion, carbohydrate offers advantagesover fat as a substrate because it pro-vides a greater yield of ATP per vol-ume of oxygen that can be deliveredto the mitochondria,3 thus improvinggross exercise efficiency.31 Third, thereis significant evidence that the per-formance of prolonged sustained orintermittent high-intensity exercise isenhanced by strategies that maintainhigh carbohydrate availability (ie,match glycogen stores and bloodglucose to the fuel demands of exer-cise), whereas depletion of thesestores is associated with fatigue in theform of reduced work rates, impaired


Table. Summary of guidelines for carbohydrate intake by athletes36

SituationCarbohydratetargets

Comments on type and timingof carbohydrate intake

Daily needs for fuel and recovery1. The following targets are intended to provide high carbohydrate availability (ie, to meet the carbohydrate needs of the

muscle and central nervous system) for different exercise loads for scenarios where it is important to exercise with highquality and/or at high intensity. These general recommendations should be fine-tuned with individual consideration oftotal energy needs, specific training needs, and feedback from training performance.

2. On other occasions, when exercise quality or intensity is less important, it may be less important to achieve thesecarbohydrate targets or to arrange carbohydrate intake over the day to optimize availability for specific sessions. In thesecases, carbohydrate intake may be chosen to suit energy goals, food preferences, or food availability.

3. In some scenarios, when the focus is on enhancing the training stimulus or adaptive response, low carbohydrateavailability may be deliberately achieved by reducing total carbohydrate intake, or by manipulating carbohydrate intakerelated to training sessions (eg, training in a fasted state or undertaking a second session of exercise without adequateopportunity for refuelling after the first session).

Light � Low intensity orskill-based activities

3-5 g/kg of athlete’sbody weight/d

� Timing of intake of carbohydrate over theday may be manipulated to promote highcarbohydrate availability for a specificsession by consuming carbohydratebefore or during the session, or duringrecovery from a previous session

� Otherwise, as long as total fuel needs areprovided, the pattern of intake may simplybe guided by convenience and individual choice

� Athletes should choose nutrient-richcarbohydrate sources to allow overallnutrient needs to be met

Moderate � Moderate exerciseprogram (eg, w1 h/d)

5-7 g/kg/d

High � Endurance program(eg, 1-3 h/d moderate tohigh-intensity exercise)

6-10 g/kg/d

Very high � Extreme commitment(eg, >4-5 h/d moderateto high-intensityexercise)

8-12 g/kg/d

Acute fueling strategies e These guidelines promote high carbohydrate availability to promote optimal performance duringcompetition or key training sessions

General fuelingup

� Preparation for events90 min of sustained/intermittent exercise

36-48 h of 10-12 g/kgbody weight/24 h

Speedyrefueling

� 60 min 1-4 g/kg consumed1-4 h beforeexercise

� Timing, amount, and type of carbohydratefoods and drinks should be chosen to suitthe practical needs of the event andindividual preferences/experiences

� Choices high in fat/protein/fiber may needto be avoided to reduce risk ofgastrointestinal issues during the event

� Low glycemic index choices may providea more sustained source of fuel forsituations where carbohydrate cannot beconsumed during exercise


FROM THE ACADEMY


Table. Summary of guidelines for carbohydrate intake by athletes36 (continued)

SituationCarbohydratetargets

Comments on type and timingof carbohydrate intake

During briefexercise

� 2.5-3 h Up to 90 g/h � As above� Higher intakes of carbohydrate are

associated with better performance� Products providing multiple transportable

carbohydrates (Glucose:fructose mixtures)achieve high rates of oxidation ofcarbohydrate consumed during exercise

FROM THE ACADEMY

skill and concentration, and increasedperception of effort. These findingsunderpin the various performancenutrition strategies, to be discussedsubsequently, that supply carbohy-drate before, during, and in the re-covery between events to enhancecarbohydrate availability.Finally, recent work has identified

that in addition to its role as a musclesubstrate, glycogen plays importantdirect and indirect roles in regulatingthe muscle’s adaptation to training.32

The amount and localization ofglycogen within muscle cells alters thephysical, metabolic, and hormonalenvironment in which the signaling re-sponses to exercise are exerted. Specif-ically, starting a bout of endurance


exercise with low muscle glycogencontent (eg, by undertaking a secondtraining session in the hours after theprior session has depleted glycogenstores) produces a coordinated upregu-lation of the transcriptional and post-translational responses to exercise. Anumber of mechanisms underpin thisoutcome, including increasing the ac-tivity of molecules that have a glycogenbinding domain, increasing free fattyacid availability, changing osmoticpressure in the muscle cell, andincreasing catecholamine concentra-tions.32 Strategies that restrict exoge-nous carbohydrate availability (eg,exercising in a fasted state or withoutcarbohydrate intake during the session)also promote an extended signaling

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response, albeit less robustly than is thecase for exercise with low endogenouscarbohydrate stores.33 These strategiesenhance the cellular outcomes ofendurance training such as increasedmaximal mitochondrial enzyme activ-ities and/or mitochondrial content andincreased rates of lipid oxidation, withthe augmentation of responses likely tobe explained by enhanced activation ofkey cell signaling kinases (eg, AMPK andp38MAPK), transcription factors (eg,p53 and PPARd) and transcriptionalcoactivators (eg, PGC-1a).33 Deliberateintegration of such training-dietarystrategies (“train low”) within the per-iodized training program is becoming arecognized,34 although potentially mis-used,33 part of sports nutrition practice.


FROM THE ACADEMY

Individualized recommendations fordaily intakes of carbohydrate should bemade in consideration of the athlete’straining/competition program and therelative importance of undertaking itwith high or low carbohydrate accord-ing to the priority of promoting theperformance of high quality exercise vsenhancing the training stimulus oradaptation, respectively. Unfortunately,we lack sophisticated information onthe specific substrate requirements ofmany of the training sessions under-taken by athletes; therefore, we mustrely on guesswork, supported by in-formation on work requirements ofexercise from technologies such asconsumer-based activity and heart ratemonitors,35 power meters, and globalpositioning systems.General guidelines for the suggested

intake of carbohydrate to provide highcarbohydrate availability for desig-nated training or competition sessionscan be provided according to the ath-lete’s body size (a proxy for the size ofmuscle stores) and the characteristicsof the session (see the Table). Thetiming of carbohydrate intake over theday and in relation to training can alsobe manipulated to promote or reducecarbohydrate availability.36 Strategiesto enhance carbohydrate availabilityare covered in more detail in relation tocompetition eating strategies. Never-theless, these fueling practices are alsoimportant for supporting the high-quality workouts within the perio-dized training program. Furthermore, itis intuitive that they add value in fine-tuning intended event eating strate-gies, and for promoting adaptationssuch as gastrointestinal tolerance andenhanced intestinal absorption37 thatallow competition strategies to be fullyeffective. During other sessions of thetraining program, it may be lessimportant to achieve high carbohy-drate availability, or there may be somevalue in deliberately exercising withlow carbohydrate availability toenhance the training stimulus oradaptive response. Various tactics canbe used to permit or promote low car-bohydrate availability, includingreducing total carbohydrate intake ormanipulating the timing of training inrelation to carbohydrate intake (eg,training in a fasted state, undertakingtwo bouts of exercise in close prox-imity without opportunity for refuelingbetween sessions).38


Specific questions examined via theevidence analysis on carbohydrateneeds for training are summarized inthe Table and show good evidence thatneither the glycemic load nor glycemicindex of carbohydrate-rich meals affectsthe metabolic nor performance out-comes of training once carbohydrateand energy content of the diet havebeen taken into account (Question #11).Furthermore, although there is soundtheory behind the metabolic advantagesof exercising with low carbohydrateavailability on training adaptations, thebenefits to performance outcomes arecurrently unclear (Figure 1, Question#10). This possibly relates to the limi-tations of the few available studies inwhich poor periodization of this tacticwithin the training program has meantthat any advantages to training adapta-tions have been counteracted by thereduction in training intensity andquality associated with low carbohy-drate variability. Therefore, a more so-phisticated approach is needed tointegrate this training/nutrient interac-tion into the larger training program.33

Finally, although there is support forconsuming multiple forms of carbohy-drate which facilitate more rapidabsorption, evidence to support thechoice of special blends of carbohydrateto support increased carbohydrateoxidation during training sessions ispremature (Question #9).

Protein. Dietary protein interactswith exercise, providing both a triggerand a substrate for the synthesis ofcontractile and metabolic proteins39,40

as well as enhancing structuralchanges in nonmuscle tissues such astendons41 and bones.42 Adaptationsare thought to occur by stimulation ofthe activity of the protein syntheticmachinery in response to a rise inleucine concentrations and the provi-sion of an exogenous source of aminoacids for incorporation into new pro-teins.43 Studies of the response toresistance training show upregulationof muscle protein synthesis (MPS)for at least 24 hours in response toa single session of exercise, withincreased sensitivity to the intakeof dietary protein over this period.44

This contributes to improvementsin skeletal muscle protein accretionobserved in prospective studies thatincorporate multiple protein feedingsafter exercise and throughout the

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day. Similar responses occur followingaerobic exercise or other exercisetypes (eg, intermittent sprint activitiesand concurrent exercise), albeit withpotential differences in the type ofproteins that are synthesized. Recentrecommendations have underscoredthe importance of well-timed proteinintake for all athletes even if musclehypertrophy is not the primarytraining goal, and there is now goodrationale for recommending dailyprotein intakes that are well above theRecommended Dietary Allowance(RDA)39 to maximize metabolic adap-tation to training.40

Although classical nitrogen balancework has been useful for determiningprotein requirements to prevent defi-ciency in sedentary humans in energybalance,45 athletes do not meet thisprofile and achievingnitrogenbalance issecondary to an athlete with the pri-mary goal of adaptation to training andperformance improvement.40 Themodern view for establishing recom-mendations for protein intake in ath-letes extends beyond theDRIs. Focus hasclearly shifted to evaluating the benefitsof providing enough protein at optimaltimes to support tissues with rapidturnover and augment metabolic adap-tations initiated by training stimulus.Future research will further refine rec-ommendations directed at total dailyamounts, timing strategies, quality ofprotein intake, and provide new rec-ommendations for protein supplementsderived from various protein sources.

Protein needs. Current data suggestthat dietary protein intake necessary tosupport metabolic adaptation, repair,remodeling, and for protein turnovergenerally ranges from 1.2 to 2.0 g/kg/day. Higher intakes may be indicated forshort periods during intensified trainingor when reducing energy intake.26,39

Daily protein intake goals should bemet with a meal plan providing a reg-ular spread of moderate amounts ofhigh-quality protein across the day andfollowing strenuous training sessions.These recommendations encompassmost training regimens and allow forflexible adjustments with periodizedtraining and experience.46,47 Althoughgeneral daily ranges are provided, in-dividuals should no longer be solelycategorized as strength or endur-ance athletes and provided with staticdaily protein intake targets. Rather,


FROM THE ACADEMY

guidelines should be based aroundoptimal adaptation to specific sessionsof training/competition within a perio-dized program, underpinned by anappreciation of the larger context ofathletic goals, nutrient needs, energyconsiderations, and food choices. Re-quirements can fluctuate based on“trained” status (eg, experienced ath-letes requiring less), training (eg, ses-sions involving higher frequency andintensity, or a new training stimulus athigher end of protein range), carbohy-drate availability, and most importantly,energy availability.46,48 The consump-tion of adequate energy, particularlyfrom carbohydrates, to match energyexpenditure, is important so that aminoacids are spared for protein synthesisand not oxidized.49 In cases of energyrestriction or sudden inactivity as oc-curs as a result of injury, elevated pro-tein intakes as high as 2.0 g/kg/dayor higher26,50 when spread over theday may be advantageous in prevent-ing FFM loss.39 More detailed reviewsof factors that influence changing pro-tein needs and their relationship tochanges in protein metabolism andbody composition goals can be foundelsewhere.51,52

Protein timing as a trigger formetabolic adaptation. Laboratory-based studies show that MPS is opti-mized in response to exercise by theconsumption of high biological valueprotein, providing w10 g essentialamino acids in the early recoveryphase (0 to 2 hours after exercise).40,53

This translates to a recommendedprotein intake of 0.25 to 0.3 g/kg BWor 15 to 25 g protein across the typicalrange of athlete body sizes, althoughthe guidelines may need to be fine-tuned for athletes at extreme ends ofthe weight spectrum.54 Higher doses(ie, >40 g dietary protein) have notyet been shown to further augmentMPS and may only be prudent for thelargest athletes, or during weightloss.54 The exercise-enhancement ofMPS, determined by the timing andpattern of protein intake, responds tofurther intake of protein within the24-hour period after exercise,55 andmay ultimately translate into chronicmuscle protein accretion and func-tional change. Whereas proteintiming affects MPS rates, the magni-tude of mass and strength changes


over time are less clear.56 However,longitudinal training studies currentlysuggest that increases in strengthand muscle mass are greatest withimmediate postexercise provision ofprotein.57

Whereas traditional protein intakeguidelines focused on total proteinintake over the day (grams per kilo-gram), newer recommendations nowhighlight that the muscle adaptation totraining can be maximized by ingestingthese targets as 0.3 g/kg BW after keyexercise sessions and every 3 to 5hours over multiple meals.47,54,58

Question #8 (Figure 1) summarizesthe weight of the current literatureof consuming protein on protein-specific metabolic responses duringrecovery.

Optimal protein sources. High-qual-ity dietary proteins are effective for themaintenance, repair, and synthesis ofskeletal muscle proteins.59 Chronictraining studies have shown that theconsumption of milk-based protein af-ter resistance exercise is effective inincreasing muscle strength and favor-able changes in body composi-tion.57,60,61 In addition, there arereports of increased MPS and proteinaccretion with whole milk, lean meat,and dietary supplements, some ofwhich provide the isolated proteinswhey, casein, soy, and egg. To date,dairy proteins seem to be superior toother tested proteins, largely due toleucine content and the digestion andabsorptive kinetics of branched-chainamino acids in fluid-based dairyfoods.62 However, further studies arewarranted to assess other intact high-quality protein sources (eg, egg, beef,pork, and concentrated vegetable pro-tein) and mixed meals on the stimula-tion of mammalian target of rapamycin(mTOR) and MPS following variousmodes of exercise. When whole-foodprotein sources are not convenient oravailable, then portable, third-partytested dietary supplements with high-quality ingredients may serve as apractical alternative to help athletesmeet their protein needs. It is impor-tant to conduct a thorough assessmentof the athlete’s specific nutrition goalswhen considering protein supple-ments. Recommendations regardingprotein supplements should be con-servative and primarily directed atoptimizing recovery and adaptation to

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training while continuing to focus onstrategies to improve or maintainoverall diet quality.

Fat. Fat is a necessary component of ahealthy diet, providing energy, essen-tial elements of cell membranes, andfacilitation of the absorption of fat-soluble vitamins. The Dietary Guide-lines for Americans8 and Eating Wellwith Canada’s Food Guide63 have maderecommendations that the proportionof energy from saturated fats be limitedto less than 10% and include sources ofessential fatty acids to meet adequateintake recommendations. Intake of fatby athletes should be in accordancewith public health guidelines andshould be individualized based ontraining level and body compositiongoals.46

Fat, in the form of plasma free fattyacids, intramuscular triglycerides, andadipose tissue provides a fuel sub-strate that is both relatively plentifuland increased in availability to themuscle as a result of endurancetraining. However, exercise-inducedadaptations do not appear to maxi-mize oxidation rates because they canbe further enhanced by dietary stra-tegies such as fasting; acute pre-exercise intake of fat; and chronicexposure to high-fat, low-carbohy-drate diets.3 Although there has beenhistorical64 and recently revived65

interest in chronic adaptation tohigh-fat, low-carbohydrate diets, thepresent evidence suggests thatenhanced rates of fat oxidation canonly match exercise capacity/perfor-mance achieved by diets or strategiespromoting high carbohydrate availabil-ity at moderate intensities,64 whereasthe performance of exercise at thehigher intensities is impaired.64,66 Thisappears to occur as a result of adown-regulation of carbohydratemetabolism even when glycogen isavailable.67 Further research is war-ranted both in view of the current dis-cussions65 and the failure of currentstudies to include an adequate con-trol diet that includes contemporaryperiodized dietary approaches.68

Although specific scenarios may existwhere high-fat diets may offer somebenefits or at least the absence ofdisadvantages for performance, in gen-eral they appear to reduce rather thanenhance metabolic flexibility byreducing carbohydrate availability and


FROM THE ACADEMY

capacity to use carbohydrate effectivelyas an exercise substrate. Therefore,competitive athletes would be unwiseto sacrifice their ability to undertakehigh-quality training or high-intensityefforts during competition that coulddetermine the outcome.68

Conversely, athletes may choose toexcessively restrict their fat intake inan effort to lose BW or improve bodycomposition. Athletes should bediscouraged from chronic imple-mentation of fat intakes below 20% ofenergy intake since the reduction indietary variety often associated withsuch restrictions is likely to reduce theintake of a variety of nutrients such asfat-soluble vitamins and essential fattyacids,9 especially n-3 fatty acids. If suchfocused restrictiveness around fatintake is practiced, it should be limitedto acute scenarios such as the pre-event diet or carbohydrate-loadingwhere considerations of preferredmacronutrients or gastrointestinalcomfort have priority.

Alcohol. Alcohol consumption may bepart of a well-chosen diet and socialinteractions, but excessive alcoholconsistent with binge drinking patternsis a concerning behavior observedamong some athletes, particularly inteam sports.69 Misuse of alcohol caninterfere with athletic goals in a varietyof ways related to the negative effectsof acute intake of alcohol on the per-formance of, or recovery from, exercise,or the chronic effects of binge drinkingon health and management of bodycomposition.70 Besides the calorie loadof alcohol (7 kcal/g), alcohol suppresseslipid oxidation, increases unplannedfood consumption, and may compro-mise the achievement of body compo-sition goals. Research in this area isfraught with study design concernsthat limit direct translation to athletes.Available evidence warns against

intake of significant amounts of alcoholduring the pre-exercise period andduring training due to the direct nega-tive effects of alcohol on exercisemetabolism, thermoregulation, andskills/concentration.69 The effects ofalcohol on strength and performancemay persist for several hours evenafter signs and symptoms of into-xication or hangover are no longerpresent. In the postexercise phase,where cultural patterns in sport oftenpromote alcohol use, alcohol may


interfere with recovery by impairingglycogen storage,71 slowing rates ofrehydration via its suppressive effect onantidiuretic hormone,72 and impairingthe MPS desired for adaptation andrepair.69,73,74 In cold environments,alcohol consumption increases periph-eral vasodilation resulting in core tem-perature dysregulation75 and there arelikely to be other effects on body func-tion such as disturbances in acid-basebalance and cytokine-prostaglandinpathways, and compromised glucosemetabolism and cardiovascular func-tion.76 Binge drinking may indirectlyaffect recovery goals due to inattentiontoguidelines for recovery. Bingedrinkingis also associated with high-risk behav-iors leading to accidents and antisocialbehaviors that can be detrimental tothe athlete. In conclusion, athletes areadvised to consider both public healthguidelines and team rules regardinguse of alcohol and are encouraged tominimize or avoid alcohol consumptionduring the postexercise period whenissues of recovery and injury repair area priority.

Micronutrients. Exercise stressesmany of the metabolic pathways inwhich micronutrients are required, andtraining may result in muscle bio-chemical adaptations that increase theneed for some micronutrients. Athleteswho frequently restrict energy intake,rely on extreme weight-loss practices,eliminate one or more food groupsfrom their diet, or consume poorlychosen diets, may consume suboptimalamounts of micronutrients and benefitfrom micronutrient supplementa-tion.77 This occurs most frequently inthe case of calcium, vitamin D, iron,and some antioxidants.78-80 Single-micronutrient supplements are gener-ally only appropriate for correction ofa clinically defined medical reason(eg, iron supplements for iron defi-ciency anemia [IDA]).

Micronutrients of key interest:Iron. Iron deficiency, with or withoutanemia, can impair muscle functionand limit work capacity78,81 leading tocompromised training adaptation andathletic performance. Suboptimal ironstatus often results from limited ironintake from heme food sources andinadequate energy intake (approxi-mately 6 mg iron is consumed perw1,000 kcal).82 Periods of rapid

ION AND DIETETICS

growth, training at high altitudes,menstrual blood loss, foot-strike he-molysis, blood donation, or injury cannegatively influence iron status.79,81

Some athletes in intense training mayalso have increased iron losses insweat, urine, feces, and from intravas-cular hemolysis.

Regardless of the etiology, acompromised iron status can nega-tively influence health, physical andmental performance, and warrantsprompt medical intervention andmonitoring.83 Iron requirements for allfemale athletes may be increased by upto 70% of the estimated averagerequirement.84 Athletes who are atgreatest risk, such as distance runners,vegetarian athletes, or regular blooddonors, should be screened regularlyand aim for an iron intake greaterthan their RDA (ie, >18 mg for womenand >8 mg for men).81,85

Athletes with IDA should seek clin-ical follow-up, with therapies,including oral iron supplementation,86

improvements in diet, and a possiblereduction in activities that influenceiron loss (eg, blood donation or areduction in weight-bearing training tolessen erythrocyte hemolysis).87 Theintake of iron supplements in theperiod immediately after strenuousexercise is contraindicated becausethere is the potential for elevatedhepcidin levels to interfere with ironabsorption.88 Reversing IDA can require3 to 6 months; therefore, it is advan-tageous to begin nutrition interventionbefore IDA develops.78,81 Athletes whoare concerned about iron status or haveiron deficiency without anemia (eg,low ferritin without IDA) should adopteating strategies that promote anincreased intake of food sources ofwell-absorbed iron (eg, heme iron andnonheme ironþvitamin C foods) as thefirst line of defense. Although there issome evidence that iron supplementscan achieve performance improve-ments in athletes with iron depletionwho are not anemic,89 athletes shouldbe educated that routine, unmonitoredsupplementation is not recommended,not considered ergogenic withoutclinical evidence of iron depletion, andmay cause unwanted gastrointestinaldistress.89

Some athletes may experience atransient decrease in hemoglobin atthe initiation of training due to he-modilution, known as dilutional or


FROM THE ACADEMY

sports anemia, and may not respond tonutrition intervention. These changesappear to be a beneficial adaptation toaerobic training and do not negativelyinfluence performance.79 There is noagreement on the serum ferritin levelthat corresponds to a problematiclevel of iron depletion/deficiency, withvarious suggestions ranging from

FROM THE ACADEMY

deficiency78,79 and the literature tosupport micronutrient supplementa-tion is often marred with equivocalfindings and weak evidence. Despitethis, many athletes unnecessarilyconsume micronutrient supplementseven when dietary intake meetsmicronutrient needs. Rather than self-diagnosing the need for micronutrientsupplementation, when relevant, ath-letes should seek clinical assessment oftheir micronutrient status within alarger assessment of their overall di-etary practices. Sports dietitians canoffer several strategies for assessingmicronutrient status based on collec-tion of a nutrient intake history alongwith observing signs and symptomsassociated with micronutrient defi-ciency. This is particularly importantfor iron, vitamin D, calcium, and anti-oxidants. By encouraging athletes toconsume a well-chosen diet focused onfood variety, sports dietitians can helpathletes avoid micronutrient de-ficiencies and gain the benefits of manyother performance-promoting eatingstrategies. Public health guidelinessuch as the DRIs provide micronutrientintake recommendations for sports di-etitians to help athletes avoid bothdeficiency and safety concerns associ-ated with excessive intake. Micro-nutrient intake from dietary sourcesand fortified foods should be assessedalongside micronutrient intake from allother dietary supplements.

THEME 2: PERFORMANCENUTRITION: STRATEGIES TOOPTIMIZE PERFORMANCE ANDRECOVERY FOR COMPETITIONAND KEY TRAINING SESSIONSPre-, During-, and PosteventEatingStrategies implemented in the pre-,during-, and postexercise periods mustaddress a number of goals. First theyshould support or promote optimalperformance by addressing variousfactors related to nutrition that cancause fatigue and deterioration in theoutputs of performance (eg, power,strength, agility, skill, and concentra-tion) throughout or toward the endof the sporting event. These fac-tors include, but are not limited to,dehydration, electrolyte imbalances,glycogen depletion, hypoglycemia, gas-trointestinal discomfort/upset, and dis-turbances to acid-base balance. Fluids


or supplements consumed before, dur-ing, or in the recovery betweensessions can reduce or delay the onsetof these factors. Strategies includeincreasing or replacing key exercisefuels and providing substrates to returnthe body to homeostasis or furtheradapt to the stress incurred during aprevious exercise session. In somecases, pre-event nutrition may need toredress the effects of other activitiesundertaken by the athlete during eventpreparation such as dehydration orrestrictive eating associated with mak-ing weight in weight category sports.A secondary goal is to achieve gutcomfort throughout the event, avoid-ing feelings of hunger or discomfortand gastrointestinal upsets that maydirectly reduce the enjoyment andperformance of exercise and interferewith ongoing nutritional support. Afinal goal is to continue to providenutritional support for health andfurther adaptation to exercise, particu-larly in the case of competitive eventsthat span days and weeks (eg, tourna-ments and stage races).Nutrient needs and the practical

strategies for meeting them beforeduring, and after exercise depend on avariety of factors, including the event(mode, intensity, and duration of exer-cise), the environment, carryover ef-fects from previous exercise, appetite,and individual responses and prefer-ences. In competitive situations, rulesof the event and access to nutritionalsupport may also govern the opportu-nities for food intake. It is beyond thescope of this review to provide furtherdiscussion other than to comment thatsolutions to feeding challenges aroundexercise require experimentation andhabituation by the athlete, and areoften an area in which the foodknowledge, creativity, and practicalexperiences of the sports dietitianmake valuable contributions to anathlete’s nutrition plan. Such scenariosare also where the use of sports foodsand supplements are often most valu-able, because well-formulated productscan often provide a practical form ofnutritional support to meet specializednutrient needs.

Hydration Guidelines: Fluid andElectrolyte BalanceBeing appropriately hydrated contrib-utes to optimal health and exercise

ION AND DIETETICS

performance. In addition to the usualdaily water losses from respiration,gastrointestinal, renal, and sweatsources, athletes need to replace sweatlosses. Sweating assists with the dissi-pation of heat, generated as a byproductof muscular work but is often exacer-bated by environment conditions, andthus helps maintain body temperaturewithin acceptable ranges.104 Dehydra-tion refers to the process of losingbody water and leads to hypohydra-tion. Although it is common to inter-change these terms, there are subtledifferences since they reflect processand outcome.

Through a cascade of events, themetabolic heat generated by musclecontractions during exercise can even-tually lead to hypovolemia (decreasedplasma/blood volume) and, thus, car-diovascular strain, increased glycogenuse, altered metabolic and central ner-vous system function, and a greaterrise in body temperature.104-106 Al-though it is possible to be hypohy-drated but not hyperthermic (definedas core body temperature exceeding40�C [104�F]),107 in some scenarios theextra thermal strain associated withhypohydration can contribute to anincreased risk of life-threatening exer-tional heat illness (ie, heatstroke). Inaddition to water, sweat contains sub-stantial but variable amounts ofsodium, with lesser amounts of potas-sium, calcium, and magnesium.104 Topreserve homeostasis, optimal bodyfunction, performance, and perceptionof well-being, athletes should strive toundertake strategies of fluid manage-ment before, during, and after exercisethat maintain euhydration. Dependingon the athlete, the type of exercise, andthe environment, there are situationswhen this goal is more or lessimportant.

Although there is complexity and in-dividuality in the response to dehydra-tion, fluid deficits of >2% BW cancompromise cognitive function andaerobic exercise performances, particu-larly in hot weather.104,105,108,109 Decre-ments in the performance of anaerobicor high-intensity activities, sport-specific technical skills, and aerobic ex-ercise in a cool environment are morecommonly seen when 3% to 5% of BW islost due to dehydration.104,105 Severehypohydration with water deficits of 6%to 10% BW has more pronounced effectson exercise tolerance, decreases in


FROM THE ACADEMY

cardiac output, sweat production, andskin and muscle blood flow.107

Assuming an athlete is in energybalance, daily hydration status may beestimated by tracking early morningBW (measured upon waking and aftervoiding) because acute changes in BWgenerally reflect shifts in body water.Urinary specific gravity and urineosmolality can also be used to approxi-mate hydration status by measuring theconcentration of the solutes in urine.When assessed from a midstreamcollection of the first morning urinesample, a urinary specific gravity of

FROM THE ACADEMY

fluids, especially extracellular fluids,including plasma volume. Therefore,athletes should not be advised torestrict sodium in their postexercisenutrition particularly when large so-dium losses have been incurred.Because sweat losses and obligatoryurine losses continue during the post-exercise phase, effective rehydrationrequires the intake of a greater volumeof fluid (eg, 125% to 150%) than the finalfluid deficit (eg, 1.25 to 1.5 L fluid forevery 1 kg BW lost).104,106 Excessiveintake of alcohol in the recovery periodis discouraged due to its diuretic ef-fects. However, the previous warningsabout caffeine as a diuretic appear tobe overstated when it is habituallyconsumed in moderate (eg, 90 minutes induration may benefit from higher


glycogen stores,118 which can be ach-ieved by a technique known as carbo-hydrate loading. This protocol ofachieving supercompensation of muscleglycogen evolved from the originalstudies of glycogen storage in the 1960sand, at least in the case of trained ath-letes, can be achieved by extendingthe period of a carbohydrate-rich dietand tapering training over 48 hours36

(Table).Carbohydrate consumed in meals

and/or snacks during the 1 to 4 hourspre-exercise may continue to increasebody glycogen stores, particularly liverglycogen levels that have beendepleted by the overnight fast.117 Itmay also provide a source of gutglucose release during exercise.117 Car-bohydrate intakes of 1 to 4 g/kg, withtiming, amount, and food choicessuited to the individual, have beenshown to enhance endurance or per-formance of prolonged exercise(Table).117,119 Generally, foods with alow-fat, low-fiber, and low-moderateprotein content are the preferredchoice for this pre-event menu becausethey are less prone to cause gastroin-testinal problems and promote gastricemptying.120 Liquid meal supplementsare useful for athletes who experiencepre-event nerves or an uncertain pre-event timetable and, thus, prefer amore quickly digested option. Aboveall, the individual athlete shouldchoose a strategy that suits their situ-ation and their past experiences andcan be fine-tuned with furtherexperimentation.The intake of carbohydrate before

exercise is not always straightforwardbecause the metabolic effects of theresulting insulin response include areduction in fat mobilization and useand concomitant increase in carbohy-drate use.119 In some individuals, thiscan cause premature fatigue.121 Strate-gies to circumvent this problem includeensuring at least 1 g/kg carbohydrate inthe pre-event meal to compensate forthe increased carbohydrate oxidation,including a protein source at themeal, including some high-intensity ef-forts in the pre-exercise warm up tostimulate hepatic gluconeogenesis, andconsuming carbohydrate during theexercise.122 Another approach has beensuggested in the form of choosing pre-exercise meals from carbohydrate-richfoods with a low glycemic index,which might reduce the metabolic

ION AND DIETETICS

changes associated with carbohydrateingestion as well as providing a moresustained carbohydrate release duringexercise. Although occasional studieshave shown that such a strategy en-hances subsequent exercise capacity,123

as summarized by the EAL (Figure 1,Question #11) and others,119 pre-exercise intake of low glycemic indexcarbohydrate choices has not beenfound to provide a universal benefit toperformance even when the metabolicperturbations of pre-exercise carbohy-drate intake are attenuated. Further-more, consumption of carbohydrateduring exercise, as further advised inthe Table, dampens any effects of pre-exercise carbohydrate intake on meta-bolism and performance.124

Depending on characteristics,including the type of exercise, theenvironment, and the athlete’s prepa-ration and carbohydrate tolerance, theintake of carbohydrate during exerciseprovides a number of benefits to exer-cise capacity and performance viamechanisms such as glycogen sparing,provision of an exogenous musclesubstrate, prevention of hypoglycemia,and activation of reward centers in thecentral nervous system.116 Robustliterature on exercise carbohydratefeeding has led to the recognition thatdifferent amounts, timing, and types ofcarbohydrate are needed to achievethese different effects, and that thedifferent effects may overlap in variousevents.36,125 The Table summarizes thecurrent guidelines for exercise fueling,noting opportunities where it may playa metabolic role (events of >60 to 90minutes) and the newer concept of“mouth sensing,” where frequentexposure of the mouth and oral cavityto carbohydrate is likely to be effectivein enhancing workout and pacingstrategies via a central nervous systemeffect.126 Of course, the practicalachievement of these guidelines needsto fit the personal preferences and ex-periences of the individual athlete, andthe practical opportunities providedin an event or workout to obtainand consume carbohydrate-containingfluids or foods. A range of everydayfoods and fluids and formulated sportsproducts that include sports beveragesmay be chosen to meet these guide-lines; this includes newer productscontaining mixtures of glucose andfructose (the so-called multiple trans-portable carbohydrates) that aim to


FROM THE ACADEMY

increase total intestinal absorption ofcarbohydrates.127 Although this couldbe of use in situations of prolongedexercise where higher rates of exoge-nous carbohydrate oxidation mightsustain work intensity in the face ofdwindling muscle glycogen stores, theEAL found that evidence for benefits iscurrently equivocal (Figure 1, Question#9).Glycogen restoration is one of the

goals of postexercise recovery, partic-ularly between bouts of carbohydrate-dependent exercise where there is apriority on performance in the secondsession. Refueling requires adequatecarbohydrate intake (Table) and time.Because the rate of glycogen resyn-thesis is only w5% per hour, earlyintake of carbohydrate in the recoveryperiod (w1 to 1.2 g/kg/h during thefirst 4 to 6 hours) is useful in maxi-mizing the effective refueling time.117

As long as total intake of carbohydrateand energy is adequate and overallnutritional goals are met, meals andsnacks can be chosen from a variety offoods and fluids according to personalpreferences of type and timing ofintake.36,117 More research is needed toinvestigate how glycogen storagemight be enhanced when energy andcarbohydrate intakes are suboptimal.

Protein Intake GuidelinesProtein consumption in the immediatepre- and postexercise period is oftenintertwined with carbohydrate con-sumption because most athletesconsume foods, beverages, and supple-ments that contain bothmacronutrients.Dietaryprotein consumed in scenarios oflow-carbohydrate availability128 and/orrestricted energy intake53 during theearly postexercise recovery period hasbeen found to enhance and accelerateglycogen repletion. For example, it hasbeen established that recovery of per-formance129 and glycogen repletionrates53 were similar in athletesconsuming 0.8 g carbohydrate/kgBWþ0.4gprotein/kgBWcomparedwithathletes consuming only carbohydrate(1.2 g/kg BW). This may support exerciseperformance and benefit athletesfrequently involved in multiple trainingor competitive sessions over the sameday or successive days.Although protein intake may support

glycogen resynthesis and, when con-sumed in close proximity to strength


and endurance exercise, enhancesMPS,59,130 there is a lack of evidencefrom well-controlled studies that pro-tein supplementation directly im-proves athletic performance.131,132

However, a modest number of studieshave reported that ingesting w50 to100 g protein during the recoveryperiod leads to accelerated recovery ofstatic force and dynamic power pro-duction during delayed onset musclesoreness.133,134 Despite these findingsother studies show no performanceeffects from acute ingestion of proteinat intake levels that are much morepractical to consume on a regular basis.Furthermore, studies that imply posi-tive findings when the control groupreceives a flavored water placebo133 ora placebo that is not isocaloric are un-able to rule out the influence of post-exercise energy provision on theobserved effect.134

Protein ingestion during exerciseand during the pre-exercise periodseems to have less of an influence onMPS than the postexercise provisionof protein but may still enhancemuscle reconditioning depending onthe type of training that takes place.Coingestion of protein and carbohy-drate during 2 hours of intermittentresistance-type exercise has beenshown to stimulate MPS during theexercise period135 and may extend themetabolic adaptation window partic-ularly during ultraendurance-typeexercise bouts.136 Potential benefitsof consuming protein before and dur-ing exercise may be targeted to ath-letes focused on the MPS response toresistance exercise and those lookingto enhance recovery from ultra-endurance exercise.EAL Questions #5 to #7 (Figure 1)

summarize the literature on consumingprotein alone or in combination withcarbohydrate during recovery onseveral outcomes. More work is neededto elucidate the relevance and practi-cality of protein consumption on sub-sequent exercise performance and ifmechanisms in this context are exclu-sive to accelerating muscle glycogensynthesis. The utility of a protein sup-plement should also be measuredagainst the benefits of consuming pro-tein or amino acids from meals andsnacks that are already part of a sportsnutrition plan to meet other perfor-mance goals.

JOURNAL OF THE ACAD

Dietary Supplements andErgogenic AidsExternal and internal motives toenhance performance often encourageathletes to consider the enticing mar-keting and testimonials surroundingsupplements and sports foods. Sportssupplements represent an ever-growing industry, but a lack of regula-tion of manufacture and marketingmeans that athletes can fall victim tofalse advertising and unsubstantiatedclaims.137 The prevalence of supple-mentation among athletes has beenestimated internationally at 37% to89%, with greater frequencies beingreported among elite and older ath-letes. Motivations for use includeenhancement of performance or re-covery, improvement or maintenanceof health, an increase in energy,compensation for poor nutrition, im-mune support, and manipulation ofbody composition,138,139 yet few ath-letes undertake professional assess-ment of their baseline nutrition-relatedhabits. Furthermore, athletes’ supple-mentation practices are often guidedby family, friends, teammates, coaches,the Internet, and retailers, rather thansports dietitians and other sport sci-ence professionals.138

Considerations regarding the use ofsports foods and supplements includean assessment of efficacy and potency.In addition, there are safety concernsdue to the presence of overt and hid-den ingredients that are toxic andthe poor practices of athletes inconsuming inappropriately largedoses or problematic combinations ofproducts. The issue of compliance toantidoping codes remains a concernwith potential contamination withbanned or nonpermissible substances.This carries significant implications forathletes who compete under antidop-ing codes (eg, National CollegiateAthletic Association or World Anti-Doping Agency).139 A supplementmanufacturer’s claim of “100% pure,”“pharmaceutical grade,” “free of ban-ned substances,” “Natural HealthProduct e NHPN/NPN” (in Canada) orpossessing a drug identification num-ber are not reliable indications thatguarantee a supplement is free ofbanned substances. However, com-mercial, third-party auditing programscan independently screen dietarysupplements for banned and restricted


Category Examples Use Concerns Evidence

Sports food Sports drinksSports barsSports confectionerySports gelsElectrolyte supplementsProtein supplementsLiquid meal supplements

Practical choice to meetsports nutrition goalsespecially when access tofood, opportunities toconsume nutrients, orgastrointestinal concernsmake it difficult toconsume traditional foodand beverages

Cost is greater than wholefoodsMay be used unnecessarily or ininappropriate protocols

Burke andCato(2015)141

Medicalsupplements

Iron supplementsCalcium supplementsVitamin D supplementsMultivitamin/mineraln-3 Fatty acids

Prevention or treatmentof nutrient deficiencyunder the supervision ofappropriate medical/nutrition expert

May be self-prescribedunnecessarily withoutappropriate supervision ormonitoring

Burke andCato(2015)141

Specificperformancesupplements

Ergogenic effects Physiological effects/mechanism ofergogenic effect

Concerns regarding usea Evidence

Creatine Improves performance ofrepeated bouts of high-intensity exercise withshort recovery periods

- Direct effect oncompetitionperformance

- Enhanced capacityfor training

Increases creatine andphosphocreatineconcentrationsMay also have othereffects such asenhancement ofglycogen storage anddirect effect on muscleprotein synthesis

Associated with acute weightgain (0.6-1 kg), which may beproblematic in weight-sensitivesportsMay cause gastrointestinaldiscomfortSome products may notcontain appropriate amounts orforms of creatine

Tarnopolsky(2010)143

Caffeine Reduces perception offatigueAllows exercise to besustained at optimalintensity/output forlonger

Adenosine antagonistwith effects on manybody targets, includingcentral nervous systemPromotes Ca2þ releasefrom sarcoplasmicreticulum

Causes side effects (eg, tremor,anxiety, increased heart rate)when consumed in high dosesToxic when consumed in verylarge dosesRules of National CollegiateAthletic Associationcompetition prohibit the intakeof large doses that produceurinary caffeine levelsexceeding 15 mg/mLSome products do not disclosecaffeine dose or may containother stimulants

Astorino andRoberson(2010)144

Tarnopolsky(2010)143

Burke andcolleagues(2013)145

Sodiumbicarbonate

Improves performance ofevents that wouldotherwise be limited byacid-base disturbancesassociated with high

When taken as an acutedose pre-exercise,increases extracellularbuffering capacity

May cause gastrointestinal side-effects that cause performanceimpairment rather than benefit

Carr andcolleagues(2011)146


Figure 2. Dietary supplements and sports foods with evidence-based uses in sports nutrition. These supplements may perform asclaimed but inclusion does not imply endorsement by this position stand.

FROM THE ACADEMY


Category Examples Use Concerns Evidence

rates of anaerobicglycolysis

- High-intensityevents of 1-7 min

- Repeated high-in-tensity sprints

- Capacity for high-intensity “sprint”during enduranceexercise

b-alanine Improves performance ofevents that wouldotherwise be limited byacid-base

Position of the Academy of Nutrition and Dietetics ... › attachments › document › a...athletic performance and emerging trends in the ﬁeld of sports nutrition. Athletes should

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