Nutrition is the fourth discipline of triathlon. You can have the fitness of your life, a perfect taper, and ideal race-day conditions -- but get your fuelling wrong and it all falls apart. Scroll through social media and you will see pros targeting 120 grams of carbs per hour, age-groupers copying them, and brands pushing ever-higher intake numbers. But what does the science actually say? A 2026 review by Plews and colleagues examined exactly this and concluded that for most age-group athletes, ultra-high carbohydrate intake (above 90 g/hour) lacks consistent scientific support and may even impair performance through gastrointestinal distress.
The Simple Version
For age-group triathletes the evidence-based sweet spot is 60-90 g of carbohydrate per hour, using a glucose-fructose mix, not the 100-120 g/hour numbers marketed to elites. Match intake to race duration: 0-30 g/hour for a Sprint, 30-60 g/hour for an Olympic, 60-80 g/hour for a Half Ironman, and 60-90 g/hour for a Full Ironman. The bike is your main fuelling window -- take 70-80% of your race calories there, starting within the first 15 minutes. Reduce intake by 10-20% on the run. Add 300-600 mg of sodium per hour (700-1000 mg/hour in heat) to avoid hyponatremia, and 3-6 mg/kg of caffeine split across the race. Nothing new on race day, and train your gut for weeks beforehand. Use the calculator at the bottom of this article for per-leg targets based on your weight, distance, and target time.
How It Works
The proven zone: 60-90 g/hour
Decades of research confirm that carbohydrate intake during prolonged exercise improves endurance performance. Jeukendrup's landmark 2014 review established clear guidelines based on exercise duration:
| Exercise Duration | Carbohydrate Recommendation |
|---|---|
| Under 1 hour | Mouth rinse or small amounts |
| 1-2 hours | Up to 30 g/hour |
| 2-3 hours | Up to 60 g/hour |
| Over 2.5 hours | Up to 90 g/hour (multiple transportable carbs) |
These recommendations reflect a physiological limit: the sodium-dependent glucose transporter (SGLT1) in the gut saturates at approximately 60 g/hour of glucose alone.
Why glucose + fructose?
Your intestine has separate transport pathways for glucose and fructose. When both are consumed together (typically in a 2:1 glucose-to-fructose ratio), total carbohydrate absorption can increase by up to 75% compared to glucose alone -- reaching 90-110 g/hour. This is why modern sport nutrition products use mixed carbohydrate formulas.
Above 90 g/hour: the evidence gets thin
The 2026 review by Plews and colleagues examined what happens beyond 90 g/hour -- the "ultra-high carbohydrate" strategies now popular among elite athletes. Their findings:
- Available studies show inconsistent results above 90 g/hour
- Higher intake increases exogenous carbohydrate oxidation but does not appear to further spare muscle glycogen
- The additional carbohydrate mainly suppresses fat oxidation rather than reducing endogenous carbohydrate use
- Gastrointestinal distress risk increases with higher doses
The review proposed three theoretical mechanisms why ultra-high intake might benefit elite athletes racing at very high intensities -- improved oxygen economy, enhanced lactate recycling, and central nervous system effects -- but emphasized that all three remain unproven.
The bottom line: intakes of 40-75 g/hour produce clear performance benefits, and intakes above 75 g/hour are not reliably more effective (Jeukendrup, 2004). For age-group triathletes, the evidence-based sweet spot remains 60-90 g/hour using mixed carbohydrate sources.
Carb intake by race distance
| Race | Typical Duration | Carbs/Hour | Rationale |
|---|---|---|---|
| Sprint | 0:50-1:30 | 0-30 g | Muscle glycogen covers most needs. Water and possibly one gel near the end. |
| Olympic | 1:45-3:00 | 30-60 g | Glycogen depletion matters beyond 2 hours. Begin fuelling early on the bike. |
| Half Ironman | 4:00-7:00 | 60-80 g | The sweet spot for structured nutrition. Most age-groupers do well at 60-70 g with a glucose-fructose mix. |
| Full Ironman | 8:00-17:00 | 60-90 g | Extended duration demands consistent fuelling. The upper range (80-90 g) only if gut-trained and using dual-source carbs. |
These are starting points. Your optimal intake depends on body weight, intensity, conditions, and individual gut tolerance.
Timing: when to eat what
Pre-race (3-4 hours before). Consume 1-4 g/kg of carbohydrate 1-4 hours before the start (Thomas et al., 2016). For a 75 kg athlete a practical target is 150-200 g at 3 hours out. Choose familiar, low-fiber, low-fat foods: oatmeal with banana and honey, white rice with jam, a bagel with peanut butter. Nothing new on race day.
Swim. Nothing. You are horizontal with your face in the water. Focus on swimming.
Bike -- your main fuelling window. Start fuelling in the first 15 minutes; do not wait until you feel hungry, because by then you are already 30-45 minutes behind. The bike is where 70-80% of your race calories should come in -- the upright position digests more easily than running. Set a timer: fuel every 20-25 minutes. First half, mix gels, sport drink, and solid food (rice cakes, bars) if tolerated; second half, shift to gels and liquid only to prepare the gut for running; last 30 minutes, one final gel with water.
Run. Reduce intake by roughly 10-20% versus the bike -- the mechanical impact of running makes absorption harder, so small frequent sips beat large amounts. Gels with water at aid stations are simplest; cola provides carbohydrate and caffeine and is often better tolerated on a stressed stomach. If nausea strikes: slow down, switch to water only for 10 minutes, then resume with diluted sport drink or cola.
Electrolytes: the forgotten factor
The ACSM recommends 0.5-0.7 g of sodium per liter of fluid during exercise longer than 1 hour (Sawka et al., 2007). More specifically, target 300-600 mg of sodium per hour in normal conditions, rising to 700-1000 mg/hour in hot (above 25 C) or humid (above 60%) environments. Keep drink concentrations below 1000 mg sodium per liter or palatability drops sharply.
Drinking plain water without electrolytes during prolonged exercise can cause exercise-associated hyponatremia -- a dangerous drop in blood sodium below 135 mmol/L, documented in events lasting more than 4-6 hours and potentially fatal. Prevention is simple: include sodium via sport drinks or electrolyte tablets.
Caffeine
Research supports 3-6 mg of caffeine per kilogram of body weight for endurance performance (Thomas et al., 2016) -- for a 75 kg athlete, 225-450 mg total across the race. Avoid it pre-race (GI issues combine badly with nerves), take a caffeinated gel or tablet mid-bike, and cola or a caffeinated gel mid-run. Split the dose rather than taking it all at once, and never introduce caffeine on race day without prior testing in training.
Example
Example: 75 kg athlete, Half Ironman, 5:30 target
With roughly a 40-minute swim, about 2:52 on the bike, and about 2:00 on the run, a Half Ironman at 60-80 g/hour breaks down like this:
| Leg | Time | Carbs | How |
|---|---|---|---|
| Pre-race (3h before) | -- | 150-225 g | Oatmeal + banana + honey |
| Swim | ~0:40 | 0 g | Nothing -- just swim |
| Bike | ~2:52 | ~170-230 g | ~4-5 gels + sport drink, starting in the first 15 min |
| Run | ~2:00 | ~100-135 g | ~2-3 gels + cola at aid stations, small frequent sips |
Total on-course carbohydrate lands around 270-365 g, roughly 5-6 gels plus 2-3 bottles of sport drink. Add 300-600 mg of sodium per hour (about 5 electrolyte tablets over the race, more in heat) and 225-375 mg of caffeine split between mid-bike and mid-run.
A beginner should sit at the lower end of every range; in hot conditions, push sodium toward 700-1000 mg/hour and slightly dilute drinks. The interactive calculator at the bottom of this article generates these numbers for your own weight, distance, target time, conditions, and experience.
Practical Rules
Practical rules (and the six most common mistakes)
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Do not copy pro strategies. The mechanisms that may help professionals racing at 85-90% VO2max differ from what matters for age-groupers at lower intensities. Optimal fuelling is intensity-dependent, not one-size-fits-all.
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Test everything in training. Every long ride and long run is a nutrition rehearsal. If you have not tested your exact products at race intensity, you are relying on hope.
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Start early. Glycogen depletion is not felt immediately. By the time you notice hunger or fading energy, the deficit is 30-45 minutes old and very hard to reverse mid-race.
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Never drink only water. Plain water over long events can cause exercise-associated hyponatremia. Always include electrolytes.
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Train your gut before raising intake. The gut is trainable, but adaptation takes weeks, not days. Jumping from 40 to 90 g/hour on race day is a recipe for GI distress. Start at 30 g/hour and build up over 4-6 weeks.
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Adjust for conditions. Heat increases sweat rate, sodium loss, and GI stress. Have a hot-weather contingency: more electrolytes, slightly lower carbohydrate concentration, more frequent small sips.
Evidence Base
Evidence base
Jeukendrup (2014) provided the definitive framework for carbohydrate intake during exercise, grounded in his research on intestinal absorption. His central finding -- that glucose absorption via SGLT1 saturates near 60 g/hour, but adding fructose (absorbed via GLUT5) allows total oxidation rates up to about 90 g/hour -- reshaped fuelling strategy for long-course racing and established the concept of gut training. His earlier work (2004) had already shown a dose-response with a ceiling: benefits scaled up to roughly 75 g/hour and then plateaued.
Plews, Booth, Krieger and Maunder (2026) examined the now-popular ultra-high carbohydrate strategies (above 90 g/hour) and found the supporting evidence inconsistent, particularly for the sub-elite athletes copying elite protocols. They noted that beyond 90 g/hour, additional carbohydrate mainly suppresses fat oxidation rather than sparing muscle glycogen, and that the proposed elite-specific mechanisms remain unproven -- while GI distress risk rises with dose.
The ACSM/AND/DC joint position statement (Thomas, Erdman & Burke, 2016) anchors the pre-race (1-4 g/kg, 1-4 hours before) and caffeine (3-6 mg/kg) recommendations. The ACSM Position Stand on fluid replacement (Sawka et al., 2007) and endurance-nutrition reviews (Vitale & Getzin; Tiller et al., 2019) provide the sodium guidance (300-1000 mg/hour depending on conditions) and the hyponatremia warning that make electrolytes a non-negotiable part of any plan longer than an hour.
Taken together, the literature points to the same practical conclusion: for age-group triathletes, a well-rehearsed 60-90 g/hour of mixed carbohydrate, paired with deliberate sodium intake, beats chasing the ultra-high numbers marketed to professionals.