Scroll through social media and you'll see pros targeting 120 grams of carbs per hour. Age-groupers copying them. Brands pushing higher and higher intake numbers. But what does the science actually say?
A comprehensive review published in Sports Medicine in 2026 by Plews et al. examined this exact question. Their conclusion: 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[1].
This guide gives you a science-based framework for race nutrition, plus a calculator that tells you exactly what you need based on your race distance, body weight, and target time.
The Science of Carb Intake During Exercise
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 in Sports Medicine established clear guidelines based on exercise duration[2]:
- Exercise 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 (using multiple transportable carbohydrates)
These recommendations reflect a key physiological limit: the sodium-dependent glucose transporter (SGLT1) in the gut saturates at approximately 60 g/hour of glucose alone [2].
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 [2]. 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 so-called “ultra-high carbohydrate” strategies now popular among elite athletes[1]. 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 [1].
The bottom line
As Jeukendrup's earlier work established, there is a dose-response relationship for carbohydrate intake during prolonged exercise, but it has a ceiling [3]. Studies providing 40-75 g/hour observed clear performance benefits. Intakes higher than 75 g/hour did not appear more effective than intakes within this range [3].
For age-group triathletes, the evidence-based sweet spot remains 60-90 g/hour using mixed carbohydrate sources.
Carb Intake by Race Distance
Based on the duration-dependent guidelines from Jeukendrup (2014)[2] and the practical recommendations from Plews et al. (2026) [1]:
| Race | Duration | Carbs/Hour | Rationale |
|---|---|---|---|
| Sprint | 0:50-1:30 | 0-30g | Muscle glycogen covers most energy needs. Water and possibly one gel near the end. |
| Olympic | 1:45-3:00 | 30-60g | Glycogen depletion becomes a factor beyond 2 hours. Begin fuelling early on the bike. |
| Half Ironman | 4:00-7:00 | 60-80g | The sweet spot for structured nutrition. Most age-groupers perform well at 60-70g with a glucose-fructose mix. |
| Full Ironman | 8:00-17:00 | 60-90g | Extended duration demands consistent fuelling. Upper range (80-90g) only if gut-trained and using dual-source carbs. |
These are starting points. Your actual optimal intake depends on body weight, exercise intensity, environmental conditions, and individual gut tolerance.
Timing: When to Eat What
Pre-race (3-4 hours before start)
The joint position statement of the American College of Sports Medicine, the Academy of Nutrition and Dietetics, and Dietitians of Canada recommends 1-4 grams of carbohydrate per kilogram of body weight, consumed 1-4 hours before exercise [4]. For a 75kg athlete, this means 75-300g — a practical target is 150-200g at 3 hours before start.
Choose familiar, low-fiber, low-fat foods: oatmeal with banana and honey, white rice with jam, bagel with peanut butter. Nothing new on race day.
Swim leg
Nothing. You are horizontal, face in water. Focus on swimming.
T1 → Bike leg (your main fuelling window)
Start fuelling in the first 15 minutes on the bike. Do not wait until you feel hungry — by that point, you are already 30-45 minutes behind on nutrition.
The bike leg is where 70-80% of your race calories should come in. The upright position allows easier digestion compared to running. Set a timer on your watch: every 20-25 minutes, take fuel.
- First half: mix of gels, sport drink, and solid food (rice cakes, bars) if tolerated
- Second half: transition to gels and liquid only to prepare the gut for running
- Last 30 minutes: one final gel with water
T2 → Run leg
Reduce intake by approximately 10-20% compared to the bike. The mechanical impact of running makes absorption harder. Small sips frequently work better than large amounts at once.
Gels with water at aid stations are the simplest approach. Cola provides carbohydrate, caffeine, and is often better tolerated on a stressed stomach.
If nausea occurs: slow down, switch to water only for 10 minutes, then resume with diluted sport drink or cola.
Electrolytes: The Forgotten Factor
Sodium
The ACSM Position Stand on Exercise and Fluid Replacement recommends 0.5-0.7 grams of sodium per liter of fluid consumed during exercise lasting longer than 1 hour [5].
A systematic review on sodium intake in endurance sports provides more specific guidance: 300-600 mg of sodium per hour under normal conditions, increasing to 700-1000 mg/hour in hot (above 25°C) or humid (above 60%) environments [6]. Sodium concentrations above 1000 mg per liter in drinks should be avoided as palatability decreases significantly [6].
Hyponatremia: the risk of plain water
Drinking plain water without electrolytes during prolonged exercise can lead to exercise-associated hyponatremia — a dangerous drop in blood sodium below 135 mmol/L [5]. This condition has been documented in events lasting more than 4-6 hours and can be fatal in severe cases.
Prevention is straightforward: include sodium in your hydration strategy, either through sport drinks or electrolyte tablets.
Caffeine
Research supports caffeine doses of 3-6 mg per kilogram of body weight for endurance performance [4]. For a 75kg athlete, this translates to 225-450 mg total across the race.
Practical timing for triathlon:
- Avoid pre-race (may cause GI issues with pre-race nerves)
- Mid-bike (km 50-60): caffeinated gel or caffeine tablet
- Mid-run (km 10-15): cola at aid station or caffeinated gel
- Split the dose rather than consuming all at once
Never introduce caffeine on race day without prior testing in training.
Common Mistakes
1. Copying pro strategies. Plews et al. specifically address this: the mechanisms that may benefit professionals racing at 85-90% VO2max are likely different from those relevant to age-group athletes at lower intensities[1]. Optimal fuelling is intensity-dependent, not one-size-fits-all.
2. Not testing 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.
3. Starting too late. Glycogen depletion is not immediately felt. By the time you experience hunger or energy loss, the deficit is 30-45 minutes old and very difficult to reverse mid-race.
4. Drinking only water. The ACSM has documented cases of exercise-associated hyponatremia caused by excessive plain water intake during prolonged endurance events [5]. Always include electrolytes.
5. Increasing intake without gut training. Jeukendrup notes that the gut is trainable — regular practice with carbohydrate intake during exercise can improve tolerance and absorption [2]. But this adaptation takes weeks, not days. A sudden jump from 40 to 90 g/hour on race day is a recipe for GI distress.
6. Ignoring conditions. Hot weather increases sweat rate, sodium loss, and GI stress. Your nutrition plan needs a hot-weather contingency: more electrolytes, slightly reduced carbohydrate concentration, more frequent small sips.
Your Personal Nutrition Plan
Enter your details below. The calculator turns the science above into per-leg carb, sodium, and caffeine targets and a rough product list — presented as ranges, because the evidence supports a window, not a single number.
Your race
Race timeline
- Pre-race (3h before)150–225g carbs
Oatmeal + banana + honey, or another familiar low-fibre meal.
- Swim (0:40)Nothing
Face in the water — just swim.
- Bike (2:52)172–229g carbs
~5 gels + sport drink. Start fuelling in the first 15 min.
- Run (1:59)101–135g carbs
~3 gels + cola at aid stations. Small, frequent sips.
What to pack (estimate)
- Gels (25g carbs each)~8
- Sport drink bottles (500ml, ~40g)~4
- Sodium / electrolyte tablets (~200mg)~15
- Caffeine (split across the race)225–375 mg
Estimates only. Ranges reflect the 60-90 g/hour evidence window, not a precise per-athlete prescription. Always rehearse in training and adjust to your own gut tolerance.
How Motus Helps Your Race Nutrition
Your race nutrition should match your race plan. Motus connects the dots:
- Goal Prediction calculates your expected finish time and race splits — the calculator above uses these to estimate nutrition needs per leg.
- Training Load Tracking shows whether you arrive at race day fit and fresh — fatigue affects gut absorption.
- AI Coach can discuss your nutrition strategy in the context of your training.
Plan Your Race with Motus
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- [1]Plews DJ, Booth PD, Krieger T, Maunder E. Fuelled or Fooled? Examining the Evidence and Mechanisms Behind Ultra-High Carbohydrate Intake in Endurance Athletes. Sports Medicine. 2026. doi: 10.1007/s40279-026-02462-z
- [2]Jeukendrup A. A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise. Sports Medicine. 2014;44(Suppl 1):S25-S33. doi: 10.1007/s40279-014-0148-z
- [3]Jeukendrup AE. Carbohydrate Intake During Exercise and Performance. Nutrition. 2004;20(7-8):669-677.
- [4]Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Acad Nutr Diet. 2016;116(3):501-528.
- [5]Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine Position Stand: Exercise and Fluid Replacement. Med Sci Sports Exerc. 2007;39(2):377-390.
- [6]Vitale K, Getzin A. Nutrition and Supplement Update for the Endurance Athlete: Review and Recommendations. Nutrients. 2019;11(6):1289. Tiller NB et al. International Society of Sports Nutrition Position Stand: Nutritional Considerations for Single-Stage Ultra-Marathon Training and Racing. J Int Soc Sports Nutr. 2019;16(1):50.