|Monday||8:30 AM - 7:00 PM|
|Tuesday||8:30 AM - 7:00 PM|
|Wednesday||8:30 AM - 7:00 PM|
|Thursday||8:30 AM - 7:00 PM|
|Friday||8:30 AM - 7:00 PM|
|Saturday||8:30 AM - 1:00 PM|
Doctor Cell Emergencies 915-540-8444
Keywords: nutrition, diet, sport, athlete, supplements, hydration
Evidence supports a range of dietary strategies in enhancing sports performance. It is likely that combining several strategies will be of greater bene t than one strategy in isolation.5 Dietary strategies to enhance performance include optimizing intakes of macronutrients, micronutrients, and fluids, including their composition and spacing throughout the day. The importance of individualized or personalized dietary advice is becoming increasingly recognized,6 with dietary strategies varying according to the individual athlete’s sport, personal goals, and practicalities (eg, food preferences). “Athlete” includes individuals competing in a range of sport types, such as strength and power (eg, weight-lifting), team (eg, football), and endurance (eg, marathon running). The use of dietary supplements can enhance performance, provided these are used appropriately. This manuscript provides an overview of dietary strategies used by athletes, the efficacy of these strategies, availability of nutrition information to athletes, and risks associated with dietary supplement intake.
Maximizing Muscle Glycogen Stores Prior To Exercise
Carbohydrate loading aims to maximize an athlete’s muscle glycogen stores prior to endurance exercise lasting longer than 90 minutes. Benefits include delayed onset of fatigue (approximately 20%) and improvement in performance of 2%–3%.7 Initial protocols involved a depletion phase (3 days of intense training and low carbohydrate intake) followed by a loading phase (3 days of reduced training and high carbo- hydrate intake).8,9 Further research showed muscle glycogen concentrations could be enhanced to a similar level without the glycogen-depletion phase,10 and more recently, that 24 hours may be sufficient to maximize glycogen stores.11,12 Current recommendations suggest that for sustained or intermittent exercise longer than 90 minutes, athletes should consume 10–12 g of carbohydrate per kg of body mass (BM) per day in the 36–48 hours prior to exercise.13
There appears to be no advantage to increasing pre- exercise muscle glycogen content for moderate-intensity cycling or running of 60–90 minutes, as signi cant levels of glycogen remain in the muscle following exercise.7 For exercise shorter than 90 minutes, 7–12 g of carbohydrate/kg of BM should be consumed during the 24 hours preceding.13 Some14,15 but not all16 studies have shown enhanced performance of intermittent high-intensity exercise of 60–90 minutes with carbohydrate loading.
Carbohydrate eaten in the hours prior to exercise (com- pared with an overnight fast) has been shown to increase muscle glycogen stores and carbohydrate oxidation,17 extend cycle time to exhaustion,5 and improve exercise performance.5,18 Specific recommendations for exercise of longer than 60 minutes include 1–4 g of carbohydrate/kg of BM in the 1–4 hours prior.13 Most studies have not found improvements in performance from consuming low glycemic index (GI) foods prior to exercise.19 Any metabolic or performance effects from low GI foods appear to be attenuated when carbohydrate is consumed during exercise.20,21
In longer events, carbohydrate improves performance primarily by preventing hypoglycemia and maintaining high levels of carbohydrate oxidation.6 The rate of exogenous carbohydrate oxidation is limited by the small intestine’s ability to absorb carbohydrate.6 Glucose is absorbed by the sodium- dependent transporter (SGLT1), which becomes saturated with an intake of approximately 1 g/minute. The simultaneous ingestion of fructose (absorbed via glucose transporter 5 [GLUT5]), enables oxidation rates of approximately 1.3 g/minute,24 with performance benefits apparent in the third hour of exercise.6 Recommendations reflect this, with 90 g of carbohydrate from multiple sources recommended for events longer than 2.5 hours, and 60 g of carbohydrate from either single or multiple sources recommended for exercise of 2–3 hours’ duration (Table 1). For slower athletes exercising at a lower intensity, carbohydrate requirements will be less due to lower carbohydrate oxidation.6 Daily training with high carbohydrate availability has been shown to increase exogenous carbohydrate oxidation rates.25
Hydration requirements are closely linked to sweat loss, which is highly variable (0.5–2.0 L/hour) and dependent on type and duration of exercise, ambient temperature, and athletes’ individual characteristics.35 Sodium losses linked to high temperature can be substantial, and in events of long duration or in hot temperatures, sodium must be replaced along with fluid to reduce risk of hyponatremia. 35
It has long been suggested that fluid losses greater than 2% of BM can impair performance,35 but there is controversy over the recommendation that athletes maintain BM by fluid ingestion throughout an event.37 Well-trained athletes who “drink to thirst” have been found to lose as much as 3.1% of BM with no impairment of performance in ultra-endurance events.38 Ambient temperature is important, and a review illustrated that exercise performance was preserved if loss was restricted to 1.8% and 3.2% of BM in hot and temperate conditions, respectively.39
BA is a precursor of carnosine, which is thought to have a number of performance-enhancing functions including the reduction of acidosis, regulation of calcium, and antioxidant properties.45 Supplementation with BA has been shown to 2 state; 0.9% improvement in time trials), reduce fatigue, and augment intracellular carnosine concentration.45 A systematic review concluded that BA may increase power output and working capacity and decrease feelings of fatigue, but that there are still questions about safety. The authors suggest caution in the use of BA as an ergogenic aid.46
Vitamin D is essential for the maintenance of bone health and control of calcium homeostasis, but is also important for muscle strength,47,48 regulation of the immune system,49 and cardiovascular health.50 Thus inadequate vitamin D status has potential implications for the overall health of athletes and performance. A recent review found that the vitamin D status of most athletes reflects that of the population in their locality, with lower levels in winter, and athletes who train predominantly indoors are at greater risk of deficiency.51 There are no dietary vitamin D recommendations for athletes; however, for muscle function, bone health, and avoidance of respiratory infections, current evidence supports maintenance of serum 25-hydroxy vitamin D (circulating form) concentrations of 80–100 nmol/L.51
Recovery from a bout of exercise is integral to the athlete’s training regimen. Without adequate recovery of carbohydrate, protein, fluids, and electrolytes, beneficial adaptations and performance may be hampered.
With less than 8 hours between exercise sessions, it is recommended that for maximal glycogen synthesis, 1.0–1.2 g/kg/hour is consumed for the first 4 hours, followed by resumption of daily carbohydrate requirements.13 Additional protein has been shown to enhance glycogen synthesis rates when carbohydrate intake is suboptimal.56 The consumption of moderate to high GI foods post exercise is recommended;13 however, when either a high-GI or low-GI meal was consumed after glycogen-depleting exercise, no performance differences were seen in a 5 km cycling time trial 3 hours later.57
Only a few studies have investigated the effect of timing of protein intake post exercise. No significant difference in MPS was observed over 4 hours post exercise when a mixture of essential amino acids and sucrose was fed 1 hour versus 3 hours after resistance exercise.60 Conversely, when a protein and carbohydrate supplement was provided immediately versus 3 hours after cycling exercise, leg protein synthesis increased threefold over 3 hours.61 A meta-analysis found timed post exercise protein intake becomes less important with longer recovery periods and adequate protein intake,62 at least for resistance training.
Dose–response studies suggest approximately 20 g of high-quality protein is sufficient to maximize MPS at rest,63 following resistance,63,64 and after high-intensity aerobic exercise.65 Rate of MPS has been found to approximately triple 45–90 minutes after protein consumption at rest, and then return to baseline levels, even with continued availability of circulating essential amino acids (termed the “muscle full” effect).66 Since exercise-induced protein synthesis is elevated for 24–48 hours following resistance exercise67and 24–28 hours following high-intensity aerobic exercise,68 and feeding protein post exercise has an additive effect,58,64 then multiple feedings over the day post exercise might maximize muscle growth. In fact, feeding 20 g of whey protein every 3 hours was subsequently found to maximally stimulate muscle myofibrillar protein synthesis following resistance exercise.69,70
In resistance training, where post exercise intake of protein was balanced by protein intake later in the day, increased adaptation of muscle hypertrophy resulted in equivocal strength performance effects.71,72 Most studies have not found a subsequent bene t to aerobic performance with post exercise protein consumption.73,74 However, in two well controlled studies in which post exercise protein intake was balanced by protein intake later in the day, improvements were seen in cycling time to exhaustion75 and in cycling sprint performance.76
Athletes eat several times per day, with snacks contributing to energy requirements.79 Dietary intake differs across sports, with endurance athletes more likely to achieve energy and carbohydrate requirements compared to athletes in weight-conscious sports.79 A review found daily intakes of carbohydrate were 7.6 g/kg and 5.7 g/kg of BM for male and female endurance athletes, respectively.80 Ten elite Kenyan runners met macronutrient recommendations but not guide- lines for fluid intake.81 A review of fluid strategies showed a wide variability of intake across sports, with several factors influencing intake, many outside the athlete’s control.82
Nutrition information may be delivered to athletes by a range of people (dietitians, nutritionists, medical practitioners, sports scientists, coaches, trainers) and from a variety of sources (nutrition education programs, sporting magazines, the media and Internet).83 Of concern is the provision of nutrition advice from outside various professional’s scope of practice. For example, in Australia 88% of registered exercise professionals provided nutrition advice, despite many not having adequate nutrition training.84 A study of Canadian high-performance athletes from 34 sports found physicians ranked eighth and dietitians, 16th as choice of source of dietary supplement information.85
Athletes take supplements for many reasons, including for proposed performance benefits, for prevention or treatment of a nutrient deficiency, for convenience, or due to fear of “missing out” by not taking a particular supplement.41
The potential benefits (eg, improved performance) of taking a dietary supplement must outweigh the risks.86,87 There are few permitted dietary supplements available that have an ergogenic effect.87,89 Dietary supplementation cannot compensate for poor food choices.87 Other concerns include lack of efficacy, safety issues (toxicity, medical concerns), negative nutrient interactions, unpleasant side effects, ethical issues, financial expense, and lack of quality control.41,86,87 Of major concern, is the consumption of prohibited substances by the World Anti-Doping Agency (WADA).
Inadequate regulation in the supplement industry (com- pounded by widespread Internet sales) makes it difficult for athletes to choose supplements wisely.41,86,87 In 2000–2001, a study of 634 different supplements from 13 countries found that 94 (14.8%) contained undeclared steroids, banned by WADA.90 Many contaminated supplements were routinely used by athletes (eg, vitamin and mineral supplements).86 Several studies have confirmed these findings. 41,86,89
In an effort to educate athletes about sports-supplement use, the Australian Institute of Sport’s sports-supplement program categorizes supplements according to evidence of efficacy in performance and risk of doping outcome.40 Category A supplements have sound evidence for use and include sports foods, medical supplements, and performance supplements. Category D supplements should not be used by athletes, as they are banned or are at high risk for contamination. These include stimulants, pro-hormones and hormone boosters, growth hormone releasers, peptides, glycerol, and colostrum.40
Athletes are always looking for an edge to improve their performance, and there are a range of dietary strategies available. Nonetheless, dietary recommendations should be individualized for each athlete and their sport and provided by an appropriately qualified professional to ensure optimal performance. Dietary supplements should be used with caution and as part of an overall nutrition and performance plan.
The authors report no conflicts of interest in this work.
Kathryn L Beck1 Jasmine S Thomson2 Richard J Swift1 Pamela R von Hurst1
1School of Food and Nutrition, Massey institute of Food Science and Technology, College of Health, Massey University Albany, Auckland, 2School of Food and Nutrition, Massey institute of Food Science and Technology, College of Health, Massey University Manawatu, Palmerston North, New Zealand
1. Burke LM, Meyer NL, Pearce J. National nutritional programs for the
2012 London Olympic Games: A systematic approach by three different
countries. In: van Loon LJC, Meeusen R, editors. Limits of Human
Endurance. Nestle Nutrition Institute Workshop Series, volume 76.
Vevey, Switzerland: Nestec Ltd; 2013:103–120.
2. Hansen EA, Emanuelsen A, Gertsen RM, Sørensen SSR. Improved
marathon performance by in-race nutritional strategy intervention.
Int J Sport Nutr Exerc Metab. 2014;24(6):645–655.
3. Hottenrott K, Hass E, Kraus M, Neumann G, Steiner M, Knechtle B.
A scientific nutrition strategy improves time trial performance by ≈6%
when compared with a self-chosen nutrition strategy in trained cyclists:
a randomized cross-over study. Appl Physiol Nutr Metab. 2012;
4. Jeukendrup AE, Martin J. Improving cycling performance: how should
we spend our time and money. Sports Med. 2001;31(7):559–569.
5. Wright DA, Sherman WM, Dernbach AR. Carbohydrate feedings
before, during, or in combination improve cycling endurance
performance. J Appl Physiol (1985). 1991;71(3):1082–1088.
6. Jeukendrup A. A step towards personalized sports nutrition: carbohydrate
intake during exercise. Sports Med. 2014;44 Suppl 1:
7. Hawley JA, Schabort EJ, Noakes TD, Dennis SC. Carbohydrateloading
and exercise performance. An update. Sports Med. 1997;24(2):
8. Bergström J, Hermansen L, Hultman E, Saltin B. Diet, muscle glycogen
and physical performance. Acta Physiol Scand. 1967;71(2):140–150.
9. Karlsson J, Saltin B. Diet, muscle glycogen, and endurance performance.
J Appl Physiol. 1971;31(2):203–206.
10. Sherman WM, Costill DL, Fink WJ, Miller JM. Effect of exercise-diet
manipulation on muscle glycogen and its subsequent utilization during
performance. Int J Sports Med. 1981;2(2):114–118.
11. Bussau VA, Fairchild TJ, Rao A, Steele P, Fournier PA. Carbohydrate
loading in human muscle: an improved 1 day protocol. Eur J Appl
12. Fairchild TJ, Fletcher S, Steele P, Goodman C, Dawson B, Fournier PA.
Rapid carbohydrate loading after a short bout of near maximal-intensity
exercise. Med Sci Sports Exerc. 2002;34(6):980–986.
13. Burke LM, Hawley JA, Wong SH, Jeukendrup AE. Carbohydrates for
training and competition. J Sports Sci. 2011;29 Suppl 1:S17–S27.
14. Raman A, Macdermid PW, Mündel T, Mann M, Stannard SR. The
effects of carbohydrate loading 48 hours before a simulated squash
match. Int J Sport Nutr Exerc Metab. 2014;24(2):157–165.
15. Balsom PD, Wood K, Olsson P, Ekblom B. Carbohydrate intake and
multiple sprint sports: with special reference to football (soccer). Int J
Sports Med. 1999;20(1):48–52.
16. Abt G, Zhou S, Weatherby R. The effect of a high-carbohydrate diet
on the skill performance of midfield soccer players after intermittent
treadmill exercise. J Sci Med Sport. 1998;1(4):203–212.
17. Coyle EF, Coggan AR, Hemmert MK, Lowe RC, Walters TJ. Substrate
usage during prolonged exercise following a preexercise meal. J Appl
Physiol (1985). 1985;59(2):429–433.
18. Neufer PD, Costill DL, Flynn MG, Kirwan JP, Mitchell JB, Houmard J.
Improvements in exercise performance: effects of carbohydrate feedings
and diet. J Appl Physiol (1985). 1987;62(3):983–988.
19. Burke LM, Collier GR, Hargreaves M. Glycemic index – a new tool
in sport nutrition? Int J Sport Nutr. 1998;8(4):401–415.
20. Burke LM, Claassen A, Hawley JA, Noakes TD. Carbohydrate intake
during prolonged cycling minimizes effect of glycemic index of preexercise
meal. J Appl Physiol (1985). 1998;85(6):2220–2226.
21. Wong SH, Chan OW, Chen YJ, Hu HL, Lam CW, Chung PK. Effect of
preexercise glycemic-index meal on running when CHO-electrolyte
solution is consumed during exercise. Int J Sport Nutr Exerc Metab.
22. Burke LM, Maughan RJ. The Governor has a sweet tooth – mouth
sensing of nutrients to enhance sports performance. Eur J Sport Sci.
23. Gant N, Stinear CM, Byblow WD. Carbohydrate in the mouth immediately
facilitates motor output. Brain Res. 2010;1350:151–158.
24. Jentjens RL, Moseley L, Waring RH, Harding LK, Jeukendrup AE.
Oxidation of combined ingestion of glucose and fructose during
exercise. J Appl Physiol (1985). 2004;96(4):1277–1284.
25. Cox GR, Clark SA, Cox AJ, et al. Daily training with high carbohydrate
availability increases exogenous carbohydrate oxidation during endurance
cycling. J Appl Physiol (1985). 2010;109(1):126–134.
26. Bartlett JD, Hawley JA, Morton JP. Carbohydrate availability and
exercise training adaptation: too much of a good thing? Eur J Sport
27. Burke LM. Fueling strategies to optimize performance: training high
or training low? Scand J Med Sci Sports. 2010;20 Suppl 2:48–58.
28. Yeo WK, Paton CD, Garnham AP, Burke LM, Carey AL, Hawley JA.
Skeletal muscle adaptation and performance responses to once a day
versus twice every second day endurance training regimens. J Appl
Physiol (1985). 2008;105(5):1462–1470.
29. Morton JP, Croft L, Bartlett JD, et al. Reduced carbohydrate availability
does not modulate training-induced heat shock protein adaptations but
does upregulate oxidative enzyme activity in human skeletal muscle.
J Appl Physiol (1985). 2009;106(5):1513–1521.
30. Horowitz JF, Mora-Rodriguez R, Byerley LO, Coyle EF. Lipolytic suppression
following carbohydrate ingestion limits fat oxidation during
exercise. Am J Physiol. 1997;273(4 Pt 1):E768–E775.
31. Volek JS, Noakes T, Phinney SD. Rethinking fat as a fuel for endurance
exercise. Eur J Sport Sci. 2015;15(1):13–20.
32. Stellingwerff T, Spriet LL, Watt MJ, et al. Decreased PDH activation
and glycogenolysis during exercise following fat adaptation
with carbohydrate restoration. Am J Physiol Endocrinol Metab.
33. van Loon LJ. Is there a need for protein ingestion during exercise?
Sports Med. 2014;44 Suppl 1:S105–S111.
34. Hillman AR, Turner MC, Peart DJ, et al. A comparison of hyperhydration
versus ad libitum fluid intake strategies on measures of
oxidative stress, thermoregulation, and performance. Res Sports Med.
35. Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ,
Stachenfeld NS; American College of Sports Medicine. American
College of Sports Medicine position stand. Exercise and fluid
replacement. Med Sci Sports Exerc. 2007;39(2):377–390.
36. Kristal-Boneh E, Glusman JG, Shitrit R, Chaemovitz C, Cassuto Y.
Physical performance and heat tolerance after chronic water loading and
heat acclimation. Aviat Space Environ Med. 1995;66(8):733–738.
37. Noakes TD. Drinking guidelines for exercise: what evidence is there that
athletes should drink “as much as tolerable”, “to replace the weight lost
during exercise” or “ad libitum”? J Sports Sci. 2007;25(7):781–796.
38. Hoffman MD, Stuempfle KJ. Hydration strategies, weight change
and performance in a 161 km ultramarathon. Res Sports Med.
Young adults don't think about disc deterioration/degeneration until it's time for the golden years. The… Read More
The lumbosacral joint is the first place chiropractors start their investigation with individuals presenting with… Read More
Tight and sore hamstrings commonly occur during workout and exercise, but can just as easily… Read More