Triathlon Nutrition: Fuelling for Swim, Bike & Run
A science-backed guide to triathlon nutrition — carb-loading, race-day fuelling across three disciplines, hydration strategy, and recovery meals.
Table of Contents
Why Triathlon Nutrition Is Different
In a single-sport race, nutrition is relatively simple — eat before, maybe during, eat after. Triathlon changes everything. You’re exercising for 1–17 hours across three disciplines, with transitions where you can’t eat. You need to fuel on the bike (where your stomach works best) to survive the run (where it doesn’t).
The single biggest reason triathletes DNF isn’t fitness — it’s nutrition. Get this right and you’ll overtake people who are fitter than you.
Pre-Race Nutrition
The Week Before
- 3 days out: Increase carbohydrate intake to 8–10g per kg of body weight. This isn’t “eating more” — it’s replacing fats and protein with carbs. Rice, pasta, bread, potatoes, fruit.
- The night before: A familiar, carb-heavy meal. Nothing new, nothing spicy, nothing high-fiber. Pasta with a simple sauce is the triathlete’s cliché for a reason.
- Race morning: Eat 2–3 hours before the start. 1–2g carbs per kg. Toast with honey, a banana, a small bowl of porridge. Coffee if you normally drink it.
Pre-Swim
- Sip water or sports drink up to 30 minutes before the gun
- Don’t eat anything in the final 30 minutes — you’ll regret it in the water
Race-Day Fuelling by Discipline
The Swim (No Fuelling)
You can’t eat during the swim. This is why pre-race nutrition matters. For sprints and Olympics, the swim is short enough that glycogen depletion isn’t a concern. For Ironman and 70.3, the swim burns 500–900 calories — you need to start replacing them immediately in T1.
T1 tip: Take a gel or a few sips of sports drink as you jog to your bike.
The Bike (Your Fuelling Window)
The bike is where you eat. Your stomach handles food best when you’re in a stable, upright-ish position with lower impact than running.
Targets by distance:
| Distance | Duration | Carbs/Hour | Total Bike Fuel |
|---|---|---|---|
| Sprint | 30–50 min | 30–40g | 1 gel + water |
| Olympic | 60–80 min | 40–60g | 2 gels + sports drink |
| 70.3 | 2:30–3:30 | 60–80g | 4–5 gels or bars + 1.5L sports drink |
| Ironman | 5:00–7:00 | 60–90g | 8–12 gels/bars + 2–3L sports drink |
Practical fuelling plan (70.3/Ironman):
- Set a timer for every 20 minutes — eat whether you feel like it or not
- Alternate between gels and solid food (rice cakes, bars) to avoid flavour fatigue
- Drink to thirst, not to a schedule — but aim for 500–800ml per hour depending on heat
- Practice every long ride — your gut needs training just like your legs
The Run (Maintenance Mode)
Your stomach is less cooperative on the run due to the jarring impact. Most athletes can only tolerate gels and liquids.
- Sprint/Olympic: Water at aid stations is enough. Maybe one gel if you feel flat.
- 70.3: 30–40g carbs per hour. One gel every 30 minutes with water. Cola at aid stations works well in the second half.
- Ironman: 30–60g carbs per hour. Gels, cola, broth, watermelon from aid stations. Walk through aid stations to eat — the 10 seconds you “lose” saves you from vomiting.
The golden rule: Nothing new on race day. Every gel, every drink, every bar should be something you’ve tested in training.
Hydration Strategy
Sweat Rate
Weigh yourself before and after a 1-hour training session (no drinking during). Each kg lost = 1 litre of sweat. This is your sweat rate. Aim to replace 70–80% of it during racing.
Electrolytes
- Sodium is the critical electrolyte. You lose 500–1500mg per litre of sweat.
- In hot races (>25°C), add sodium tablets or use high-sodium sports drinks
- Signs of low sodium: bloating, nausea, confusion. This is dangerous — don’t just drink more water.
By Conditions
- Cool (<18°C): 400–600ml/hour
- Moderate (18–25°C): 500–800ml/hour
- Hot (>25°C): 700–1000ml/hour + extra sodium
Post-Race Recovery Nutrition
Immediately After (0–30 min)
- Recovery shake or chocolate milk (20–25g protein + 40–60g carbs)
- Water or sports drink
- Don’t force solid food if you feel nauseous — liquid nutrition is fine
1–3 Hours After
- Real meal: lean protein, carbs, vegetables. A burger and fries is honestly fine.
- Continue hydrating — check urine colour (pale yellow = good)
The Next 48 Hours
- Eat normally. Don’t restrict calories.
- Extra protein (1.5–2g per kg) to help muscle repair
- Anti-inflammatory foods: berries, fatty fish, turmeric
Common Nutrition Mistakes
- Not eating enough on the bike — The #1 Ironman mistake. You feel fine at hour 2; you bonk at hour 6. Eat early, eat often.
- Trying new products on race day — Your stomach will revolt. Test everything in training.
- Drinking too much plain water — Hyponatremia (low sodium) can be life-threatening. Always include electrolytes in long races.
- Skipping breakfast — You need 300–600 calories 2–3 hours before the start. Set an alarm.
- Eating solid food on the run — Most stomachs can’t handle it. Stick to gels, liquids, and soft foods (banana, watermelon).