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Nutrition and Ergogenic Aids: Section Articles

Fueling the Triathlete: Evidence-Based Practical Advice for Athletes of All Levels

Getzin, Andrew R. MD, FACSM1; Milner, Cynthia RDN, CSSD2; Harkins, Marie MS, FNP-BC, CDE3

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Current Sports Medicine Reports: 7/8 2017 - Volume 16 - Issue 4 - p 240-246
doi: 10.1249/JSR.0000000000000386
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There are 3.5 million triathlon participants worldwide (46) (

Triathlons are endurance events that involve swimming, running, and biking. They range in distance from sprint races that can take as little as 1 h to complete up to ironman-length events which consist of a 2.4-mile swim, a 112-mile bike, and a 26.2-mile run. Most races are inclusive of participants with a broad range of fitness and individual race goals — some triathletes want to compete and some simply to complete. Unfortunately, the majority of studies on endurance athletes are small studies of well trained to elite men in a laboratory setting often engaging in long bouts of exercise. However, nearly 75% of participants that completed the 2016 USA Triathlon Annual Membership Survey stated that they mostly raced sprint-distance events within the past year (USAtriathlon). We are therefore left to extrapolate research findings in the elite triathlete to the nonelite.

Fueling appropriately during racing and training is important for participants of all levels. We consider fueling for triathletes not simply in terms of ingestion of something to produce energy but also to include products consumed preracing and pretraining or during racing and training with the goal to maximize performance. Proper execution of a fuel race plan can make the difference between a personal best and fatiguing prematurely on the run or necessitating visiting the on-course bathrooms. The goal of this article is to equip clinicians with the latest fueling information to help with successful training and racing. The recommendations are germane to individuals of all racing abilities and distances. This article is a translation and update to triathletes of a previous article written by our group that focused on the ultraendurance athlete (20). We have included our experience working with triathletes when specific research is lacking.

Carbohydrate in Fueling

Evaluation of Boston Marathon finishers, dating all the way back to the 1920s, showed that those with higher blood glucose levels postmarathon, from prerace glucose loading and race fueling, tended to perform well and fair better upon finishing (22). Carbohydrate (CHO) was and still is the primary energy source for endurance athletes including triathletes because of its importance as a fuel for muscle and central nervous system (CNS) functioning during moderate- to high-intensity endurance exercise (28). The ergogenic effects of exogenous CHO consumption during exercise are related to sparing of skeletal muscle glycogen, prevention of liver glycogen depletion and the subsequent onset of hypoglycemia and/or facilitating high rates of CHO oxidation to fuel moderate- to higher-intensity exercise (11). CNS effects of racing with low CHO availability include impaired pacing, motor skills, concentration, and an increased perception of fatigue (49). While triathletes have much higher fat stores compared to bodily CHO stores, ATP generation via fat oxidation is less efficient compared with CHO oxidation and less able to fuel high intensity training and racing.

For shorter-duration triathlons, such as the sprint distance, the 24-h period before the triathlon will provide adequate time for normalizing muscle glycogen stores and can usually be achieved by eating a CHO-rich diet of at least 6 g CHO·kg−1 body weight during the 24 h before race day (9). For triathlons lasting longer than 90 min, supercompensation of glycogen stores may be beneficial and can be achieved by most well-trained or elite-level athletes in the 36 to 48 h before competition by increasing dietary CHO intake to approximately 10 to 12 g·kg−1·d−1 (49).

On race day, the precompetition fueling goal is to “top-off” glycogen stores, especially within the liver, which may be significantly depleted after the overnight fast (9,39). CHO intake of 1 to 4 g CHO·kg−1 within 1 to 4 h before competition endurance exercise performance is recommended (9,49). Athletes should consume smaller portions of solid food closer to the event, larger portions when more time is available for digestion (9,49). Likewise, foods that are CHO-rich but low in fiber or residue, low in fat, and low to moderate in protein may be better tolerated precompetition due to more rapid gastric emptying (49). Liquid meal supplements may be a good choice for triathletes experiencing prerace anxiety because of the more rapid gastric emptying of liquids compared with solid foods (49).

Recommended CHO intake during endurance exercise is based on event duration (Table 1). For exercise lasting between 1 and 2.5 h, 30 to 60 g of CHO per hour has been found to provide adequate exogenous CHO to spare glycogen (4,9,49). For longer duration exercise/competition (>2.5 to 3 h), consuming amounts of CHO up to about 90 g of CHO per hour has been associated with faster race times (41). Gastrointestinal tolerance may be increased and increased oxidation of exogenous CHO may occur when using multiple transportable CHO sources (i.e., a mix of glucose/glucose polymers and fructose CHO sources vs. glucose alone) (26).

Table 1
Table 1:
Recommended carbohydrate intake for triathlons based on race distance.

Practical considerations unique to triathlon competition include the lack of opportunity for fueling during the swim. The cycle portion of the triathlon is the most conducive time for CHO ingestion and provides an opportunity for intake of CHO and fluid in preparation for the run. In a study of Ironman athletes, Kimber et al. (31) found that 73% of the total energy intake occurred during the cycle portion. The form of the CHO, liquid (i.e., sports drink), semisolid (i.e., gel) or solid CHO (i.e., bar or whole food) has not been shown to impact the rate of oxidation assuming adequate fluid intake (42,43).

While incorporating periods of training with lower CHO availability may be of benefit to triathletes by “upregulating” metabolic processes involved in the utilization of fat as an energy source during exercise and theoretically sparing endogenous CHO sources, a performance benefit has not been shown in “real life” and we certainly do not recommend low carbohydrate on race day (4,9,13,49).

For those athletes, struggling with fueling with CHO due to gastrointestinal (GI) intolerability, we recommend considering a CHO rinse instead of fueling. Frequent mouth rinsing with CHO solution every 5 to 10 min with a 10-s contact between the oral cavity and a CHO source seems to elicit the most reliable performance benefit which is believed to occur due to the neural effects on decreasing fatigue (9,16,27,49).


Historically, exercise-induced heat stroke was believed to be solely attributed to dehydration due to inhibited sweat evaporation secondary to decreased cutaneous blood flow with inhibited energy dissipation through evaporation. In addition, laboratory and dessert studies (not studies in actual racers) showed high fatigability in individuals with >2% dehydration thought to be due to decreased cardiac output — the rate limiting step for oxygen delivery to working muscles in most athletes (37).

Wyndham and Strydom's (54) landmark study in 1969 evaluated marathon runners in race conditions. Several runners including the winner had dangerously high rectal temperature, according to the authors, and the rectal temperature correlated with the degree of dehydration. They interpreted their data as a warning to drink more during exercise instead of a possible alternative theory that those who can sustain greater dehydration levels and higher rectal temperatures will win the race.

For years to follow, athletes were told that thirst was not a reliable indicator of hydration status, and they needed to drink continuously. Consequently, hundreds of athletes imbibed high quantities of fluids before, during, and after racing resulting in excessive free fluid lowering serum sodium concentration with resultant exercise-associated hyponatremia (EAH). Exertional hyponatremia can result in pulmonary edema and, in more severe cases, brain swelling, and death (24).

In 2003, Dr. Tim Noakes and the International Marathon Medical Directors Association presented a hydration plan with a different interpretation of the evidence (37). They said runners (and we can extrapolate to triathletes) should drink ad libitum — as thirst dictates. They recommended an approximate guide of 400 to 800 mL·h−1 with increased rates for faster or larger athletes especially in warm environmental conditions and less fluids for smaller, slower athletes or those in colder environmental condition.

While severe dehydration with exercise can result in an increase in core body temperature, the heat burden is based on the athlete's metabolic rate and can be lowered by slowing pace. There has been no compelling evidence to suggest a change in these well thought out recommendations.

More recent studies have only added support for the ad libitum fluid plan. Beis et al. (5) used retrospective video analysis of 10 elite marathoners in 13 city marathons evaluating footage from the cameraman on a motorcycle following the lead pack and showed that while a variation of fluid intake occurred, most stayed within the 400 to 800 mL·h−1 recommendation, and one of the winners had almost 10% dehydration. Wall et al. (51) had 10 well-trained cyclists perform a 2-h laboratory submaximum training session of biking and walking to produce 3% dehydration. Afterward, the athletes received blinded postexercise intravenous rehydration to return them to euhydration, 2%, or 3% dehydration. Subsequently, a 25-km time trial with a fan to simulate environmental cycling conditions did not result in a significant difference between the groups in time to completion, wattage produced, or rating of perceived exertion.

Currently, competitive cyclists are experimenting with controlled dehydration while climbing on the bike to lower overall body weight in an effort to lower wattage/kg ratio but not enough to decrease cardiac output. This strategy could provide some benefits for triathletes competing on hilly courses provided they could still handle the postbike run.

We advise triathletes to determine their individual hydration plan by initially starting with 400 to 800 mL·h−1 and listening to their thirst. Additional information on fluid needs can be gained by following the position article on exercise and fluid replacement (44) and obtaining preexercise and postexercise weights to determine sweat loss for individual workouts in specific ambient conditions to a get a sense of one's individual sweat rate. In more experienced triathletes, the plan can be altered once the athlete determines in what hydration state he or she functions best. Like all plans, it will need to be altered based on environmental and personal conditions on each individual day.


The etiology of exercise-associated muscle cramps (EAMC) has not been clearly elucidated but seems to be multifactorial involving fatigue, dehydration, and low total body sodium (19). Please refer to our previous article in this journal for a more detailed discussion of EAMC in triathletes (20). Salt losses from sweating can exceed 8 to 9 g of sodium in an Ironman Triathlon (48). In this study of South African Ironman triathletes, athletes suffering from EAMC had statistically lower serum sodium than noncrampers. In addition, while there is no direct evidence that increased sodium intake in triathletes decreases EAMC, there is evidence sodium replacement decreases EAMC in professional tennis players and miners (19). It is our clinical experience that triathletes with a history of EAMC often have borderline low serum sodium and decrease future occurrence of EAMC with sodium supplementation. The Dietary Guidelines for Americans recommends Americans ingest <2 g·d−1 of salt. However, these guidelines do not apply to normotensive triathletes who are actively training and racing with resultant sodium sweat losses. We advise normotensive triathletes, especially larger athletes, salty sweaters, and those training and competing in hot environments to exceed USDA recommendations for daily sodium intake. Athletes should consider salt loading the day before racing and ingesting salt during the race. Average sodium intake while racing long-distance triathlons in high-level triathletes is reported as <500 g·h−1 (41), which seems like a reasonable starting goal for ingestion by triathletes. The dosing can be adjusted similar to fluid intake based on GI tolerability, history of cramping with salt, and current feeling of muscle excitability while racing. Salt replacement while racing can be from drinks, gels, food, or salt tablets. The recent suspension of two professional triathletes for testing positive for the banned drug ostarine attributed to contaminates in salt tablets is a reminder to all triathletes who are taking supplements that they are not regulated by the FDA and therefore may possibly misrepresent their content (50) (


Since the 1970s, caffeine, 1,3,7-trimethylxanthine, has been a known ergogenic aide for endurance sports (15). It is a naturally occurring compound found in plant foods that is consumed on a regular basis by 90% of adults (13). It peaks in serum 15 to 120 min after ingestion with half-life 2.5 to 6 h and easily crosses the blood-brain barrier (2). While the main mechanism of caffeine’s ergogenic effect has not been proven, its structure is similar to adenosine, which helps to perpetuate the theory that its main action is adenosine inhibition in the CNS with a resultant reduced perception of effort, fatigue, or pain associated with exercise (2,47). A plausible alternative theory is glycogen sparing early in exercise that may stem from fat oxidation (18,32). Side effects progress in severity with increasing dosing. They include nausea, stool urgency and frequency, diarrhea, jitteriness, palpitations, anxiety, elevated BP, headaches, insomnia, physiologic addiction and withdrawal symptoms (40). Contrary to popular belief, caffeine consumption does induce water or electrolyte imbalances and does not cause hyperthermia. (1).

Most of the evidence for the positive ergogenic effects of caffeine on endurance sports has been demonstrated in laboratory studies with moderate to high caffeine doses (5 to 13 mg·kg−1 body mass) (8,47). However, there does not seem to be a dose-response effect but instead an all or none response with a plateau as low as 3 mg·kg−1 (8). Lower dosing may provide the same ergogenic benefits with fewer side effects (18,23,47). Initial concerns of the diuretic or hyperthermic effects of caffeine have been debunked (1). The variable responsiveness to caffeine is believed to result from CYP1A2 polymorphism, which encodes cytochrome P450 hepatic enzyme that is responsible for caffeine break down. Womack (53) evaluated 35 trained male cyclists in two computer-simulated time trials and found a greater ergogenic effect of caffeine on AA homozygotes as compared with C allele carriers. Homozygous AA carriers more rapidly metabolize caffeine, and the authors attributed benefits due to the increased effects of downstream metabolites.

We recommend consumption of relatively low dose caffeine, approximately 3 mg·kg−1 1 h before training or racing. Individuals engaging in exercise greater than a few hours should consider supplementing continued interval supplementation with lower dosing to keep blood levels high, especially at the end of events to help maintain focus. Athletes should be mindful of the cumulative effects of caffeine so as to not negatively affect sleep or develop tolerance (40). Caffeine-naive individuals may have a greater ergogenic effect with lower dosing but also are more vulnerable to potential side effects (6). While there is no proven link of caffeine use and triathlon swim deaths, we recommend caution with excessive caffeine intake preswim on race day since the prevailing theory of the swim deaths is cardiac arrhythmia (6), and it is possible that high doses of caffeine may cause palpitations or PVC and could potentially lead to arrhythmias.


Nitrate-rich beetroot juice (BRJ) has become a popular triathlon supplement due to its potential to lower oxygen utilization in submaximum workloads on trained athletes. Nitric oxide (NO) is a ubiquitous intracellular messenger that is a key regulator of vascular integrity. It is produced from the oxidation of l-arginine via the oxygen dependent enzyme NO synthase (29). Recent research has shown that it also can be generated from a non-oxygen-dependent pathway where nitrate (NO3−) is converted to nitrate (NO2−) and subsequently NO. Both acute (2.5 h preexercise) and chronic (6 d) supplementation has been shown to increase plasma nitrite concentration (13). Roughly 25% of ingested nitrate enters the enterosalivary circulation, where it is reduced to nitrite by oral bacteria. The use of antibacterial mouthwashes or gum may negatively impact NO production (35).

Larsen et al. (34) was the first to report a decrease in V˙O2 requirement with submaximum workload in nine healthy men after 3 d of 0.1 mmol·kg−1·d−1 of sodium nitrate (NaNO3−). Serum nitrate levels increased and resting systolic and diastolic blood pressure decreased in the supplemented group compared with placebo. The oxygen cost was statistically less in supplemented versus control group at 45%, 60%, 70%, and 80% of max cycling workload but not at 85% or maximum workload. Bailey et al. (3) demonstrated a similar benefit with organic nitrates in the form of BRJ. Eight men consumed 500 mL BRJ or blackcurrant cordial as placebo for 6 d. Serum nitrite levels were elevated after day 3 in those receiving BRJ. During moderate-intensity but not high-intensity step test, the O2 requirements were decreased in the BRJ. Further studies have demonstrated increased time to exhaustion and improved time trial performance (29,33).

While there is excitement about BRJ, careful review of the literature would suggest that the jury is still out. Most positive studies have been on fewer than 10 subjects. In addition, not all studies have shown a positive effect of nitrate supplementation (7,10). Finally, elite athletes seem to be less responsive to nitrate supplementation possibly due to increased organic nitrate as part of their nutrition or from increased metabolic efficiency from years of training (30).

While organic nitrate ingestion from food sources appears to be safe, caution should be taken with use of nitrate salts because they can be confused with nitrites. Excessive nitrite intake is associated with methemoglobinemia, as well as a potential risk for hypotension, especially if combined with other vasodilatory drugs (36). Also, there is a potential risk of nitrite toxicity if nitrates are inappropriately stored without refrigeration since high-nitrate containing vegetable juice can be contaminated by nitrate-reducing bacteria, leading to a buildup of nitrite over time (36).

Due to the lack of research on nitrate supplementation in longer-distance endurance events and triathlons, we suggest triathletes implement a food-first approach to increasing their nitrate intake. Athletes who choose a diet high in fruits and vegetables, such as the DASH diet, with emphasis on selecting high-nitrate foods and drinks may achieve a nitrate intake in the 5 to 9 mmol range (25). Nitrate-rich vegetables include celery, cress, chervil, lettuce, spinach, and red beetroot (which typically contain over 250 mg (4 mmol) nitrate per 100 g fresh weight). It is likely that BRJ or BRJ concentrate, when stored properly and used before expiration, are safe choices for either acute (~2.5 h before exercise) or chronic supplementation for triathletes. Those athletes who are interested in supplementation but whose palates have a hard time with BRJ might want to consider BRJ concentrate, which can be ingested as a prerace shot. More research is needed to determine if BRJ, BRJ concentrate, and/or other supplemental sources of nitrate are beneficial specifically for the triathlete and, if so, as well as to determine an appropriate dosing regimen.

Exercise-Induced Gastrointestinal Syndrome

Gastrointestinal symptoms with exercise or “exercise-induced gastrointestinal syndrome” (EIGS) can aversely effect race enjoyment and results (14). Symptoms are not restricted only to noncompetitive participants. Pfeiffer et al. (41) found that >30% IM Hawaii and IM Germany (when it was the European Championship) participants suffered from EIGS. The prevalence increases with exercise duration and increasing ambient temperature and appears to be greater with running then cycling (21,41). The etiology appears to be from a combination of splanchnic hypoperfusion, resultant intestinal epithelial injury, and delayed nutrient intestinal absorption coupled with stress-induced sympathetic drive, which alters intestinal motility (14). Costa has shown in the laboratory that the gut can be trained. Twenty-five competitive endurance and ultraendurance runners completed an initial 2 h steady-state run at 60% V˙O2max consuming 30 g CHO every 20 min followed by a 1-h distance run test at a self-selected pace. Athletes subsequently performed 10 runs over a 2-wk period for 1 h duration at 60% of V˙O2max consuming either 30 g of CHO every 20 min in solid or gel form or a placebo created to match the gel in taste and consistency. After gut training, subjects repeated the initial 2-h run and 1-h endurance test. The CHO solid and gel groups improved EIGS and running performance compared with the placebo group. The CHO solid group also reduced malabsorption and increased blood glucose availability compared with placebo.

Evidence shows that increased CHO consumption is inversely related to IM distance races finishing time but no such evidence exists for shorter course racing (42). Due to the lack of fueling studies at sprint triathlons and our professional and personal experience, we tell our athletes they are better off fueling less during short-course events as opposed to over fueling and developing exercise-induced gastrointestinal symptoms. We advise all athletes to practice their fueling strategies and be flexible on race day so as to not continue to fuel into a GI tract that is not positively responding. For longer races, slowing down pace temporarily to allow better fueling can potentially result in an improved race outcome. Athletes should be careful with fueling with the various different nutrition products available at aid stations during racing if they have not practiced fueling with those products during training for race day.


In 2011 to 2014, the U.S. prevalence of obesity (BMI > 30 kg·m2) was 36% in adults (38). While the obesity rate in triathletes is not as high, many triathletes are above the recommended BMI of 18.5 to 24.9 kg·m2. In athletes with increased muscle mass, BMI may be a less valuable measure than excessive body fat. There is a competitive disadvantage for heavier triathletes with a progressive handicap as the racer moves from the swim, to bike, to run because the effect of gravity plays a greater role (45). USA Triathlon Competitive Rules has race categories for heavier athletes: Athena for women and Clydesdale for men with a minimum weight of 165 and 220 pounds, respectively. Obese individuals should maintain an active lifestyle, which can include triathlons. Athletes can be fit and healthy while still being overweight (52). We are unaware of any studies evaluating fueling for training and racing in obese triathletes and recommend that they follow recommendations previous discussed in this article except in special circumstances (Table 2).

Table 2
Table 2:
Special considerations for the triathlete with obesity.

It may seem counterintuitive, but it is our experience providing care for obese triathletes that if they train for long-distance triathlons they tend to gain weight. Exercise for 60 to 90 min may result in weight loss if it is not counterbalanced by increased caloric intake (17). Stress from trying to fit more activities into an already busy life, disruption of sleep cycles, fueling for workouts and recovery, all potentially contribute to triathletes excessive caloric intake and subsequent weight gain. We encourage obese individuals interested in participating in triathlons to limit the distance they are training for so they can have the exercise benefits without disrupting sleep and normal nutrition patterns. Obese triathletes should be careful not to overestimate their postexercise recovery nutrition needs (Table 3).

Table 3
Table 3:
Recommended carbohydrate intake for triathlons based on race distance.

Obese patients attempting weight loss via exercise and caloric restriction on average lose approximately 10% of their body weight. We encourage obese triathletes to meet with a sports dietitian. However, many triathletes also may benefit from medication and possible bariatric surgery, which can create special situations for training and racing. Phentermine is often prescribed on its own or as a component of the weight loss medication Qsymia (Phentermine and Topiramate extended release). Phentermine is a stimulant, which causes an increased risk of hyperthermia and cardiac dysrhythmias. Topiramate may lead to metabolic acidosis. Roux-En-Y gastric bypass surgery poses the biggest challenge for nutrition recommendations during training and racing because of its malabsorptive and restrictive effects on the gastrointestinal tract. We advise caution in postbariatric surgery racers in longer races as caloric needs compete with fluid intake with minimal gastric storage capacity (12).


There is a broad-range of triathlon participants from those who want to compete to those who just want to complete over a range of race distances. While the fueling plan for training and racing varies depending on the distance, the basic foundation is the same across the spectrum and includes drinking as thirst dictates and maintaining sufficient CHO availability by prerace loading and fueling during the event. Caffeine is a proven ergogenic aid that racers may consider using with laboratory-demonstrated benefits at dosing as low as 3 mg·kg−1. While there is more research that needs to be done on sodium replacement for EAMC, currently elite triathletes regularly consume upwards of 500 mg, particularly in long races. Newer research supports the addition of organic nitrates to maximize efficiency. However, most of the studies evaluating nitrates are in small number of subjects performed from only a few laboratories across the world, and there are a number of studies that show no effect. All fueling has to be balanced with GI tolerability. Finally, as the demographic of triathlon participation is shifting to include heavier racers, clinicians, coaches, and racers need to have an understanding of some of the special needs of this population.

A.R.G. has no conflict of interests or sources of funding.

C.M. and M.H. have conflicts of interest and sources of funding.


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