Overview

Triathlon is the most nutrition-dependent endurance sport. You're asking your body to perform three different activities across potentially 6+ hours, each with different energy demands. The swim is a near-all-aerobic effort with no fuelling possible mid-race. The bike allows ~90g carbs/hour of fuelling. The run has the lowest fuel tolerance — gut distress can end a race here more often than any other cause.

This guide gives you a practical race-day fuelling plan for each triathlon distance, plus the training nutrition required to make those plans work. It assumes you've read Cycling Nutrition & Fuelling and understand the basics; this adds the multi-sport context.

Golden Rule: Triathlon nutrition is bike nutrition. Fuel heavily on the bike, eat lightly on the run, trust that what you put in during the bike is what carries you through the marathon.

Why Triathlon Nutrition Is Harder

The swim: No eating. Empty glycogen going into the swim is a bad start.

The bike: 4-6 hours in the saddle (long-course). Plenty of time to eat, absorb, recover from any gut upset. This is your fuelling window.

The run: Gut absorption is HALF what it was on the bike. Running pounds the stomach. Whatever fuel you ingest here has to be simple, practiced, and spaced.

The transitions: Two short windows (T1, T2) where you can grab quick carbs — most people miss these opportunities.

Distance-Specific Nutrition Plans

Sprint Triathlon (750m / 20km / 5km)

Total time: 60-90 minutes. Short enough that you don't really need mid-race fuel.

Pre-race (3 hours before):

400-500 kcal carb-focused breakfast: porridge with banana, honey; toast with jam; or sports nutrition breakfast if travelling
Water with small electrolyte
No fibre, no fats, no new foods

Pre-race (30 min before):

1 energy gel (25g carbs) or 200ml sports drink
Small sip of water

During the race:

Swim: nothing
Bike: small sips of water if hot. A short sprint bike (<45 min) really doesn't need fuel
Run: water at aid station if long enough / hot

After: normal meal within 1 hour

Olympic (1500m / 40km / 10km)

Total time: 2-3 hours. Now fuelling matters.

Night before: Normal dinner, carb-focused. No alcohol.

Race morning (3 hours before): 600-700 kcal breakfast, same carb-focused approach.

Pre-race (20 min): 1 gel + sips of water.

Swim: nothing.

Transition 1 (T1): grab a gel or small bottle, eat on bike.

Bike (60-90 min):

30-60g carbs in first hour
500-750ml water with electrolytes
Most athletes benefit from one gel at 30 min and sports drink throughout

Transition 2 (T2): another small gel while running out of T2 — or skip if you're sensitive.

Run (40-60 min):

Water at aid stations
Maybe one gel at halfway if you feel empty

After: recovery drink + real food within 1 hour

Half Ironman (1.9km / 90km / 21.1km)

Total time: 4.5-7 hours. Nutrition becomes a major variable.

Night before:

Normal carb-focused dinner, maybe slightly larger than usual
No alcohol, no new foods
Plenty of water with sodium

Race morning (3 hours before):

800-1000 kcal breakfast
Examples: big bowl of porridge + banana + 2 slices toast with honey + small coffee; or a specific "race breakfast" product if training in Olympic mode

Pre-race (15-30 min): 1-2 gels + small water.

Swim: nothing.

T1: grab bike nutrition. Have a gel or bar ready to eat in the first 5 minutes on the bike.

Bike (2.5-3.5 hours) — THIS IS YOUR FUELLING WINDOW:

60-90g carbs per hour — must be consistent
750-1000ml water per hour with electrolytes
Practice everything in training — NO new bars, gels, or drinks on race day

Typical bike fuel for 3 hours:

Bottle 1 (first hour): 750ml sports drink = 45g carbs
Gel at 30 min: 25g carbs
Bar at 45 min: 30g carbs
Bottle 2 (second hour): 750ml sports drink = 45g carbs
Gel at 1:30: 25g carbs
Gel at 2:00: 25g carbs
Bar at 2:15: 25g carbs
Bottle 3 (last hour): 750ml sports drink + sip of cola near end

Total: ~250g carbs, ~2250ml fluid. This is the right volume for a 3-hour bike.

T2: sip sports drink, small gel, grab run fuel. DO NOT force food here.

Run (90 min-2.5 hours):

30-60g carbs per hour, depending on gut tolerance
Water at every aid station
One gel every 20-30 min, or sports drink + solid food combo
Cola in last 5 km if available (caffeine hit + simple sugars)

Full Ironman (3.8km / 180km / 42.2km)

Total time: 10-16 hours. Nutrition is 50% of finishing.

Day before:

2 carb-focused meals (breakfast, lunch); moderate dinner
Snack on simple carbs all day (rice cakes, bananas)
Hydrate aggressively with electrolytes
No alcohol, no fibre-heavy salads

Race morning (3-4 hours before):

800-1200 kcal, simple carbs
Tested breakfast — porridge, banana, honey, toast

Pre-race (15 min before swim): 1 gel + water sip.

Swim: nothing. Just swim.

T1: Grab nutrition. Have a bar and gel in first 10 min on bike.

Bike (5-7 hours):

90g carbs per hour, pretty much continuous
750-1000ml water per hour
Sodium: 500-1000mg per hour (salt tabs, sports drink, pretzels)
Caffeine: introduce in last 2 hours (caffeinated gels)
Solid food in first half, switch to liquid/gel in second half

Sample bike fuel for 6 hours:

Hour 1: sports drink bottle (45g) + bar (30g)
Hour 2: sports drink + gel (45g + 25g)
Hour 3: sports drink + bar (45g + 30g)
Hour 4: sports drink + gel (45g + 25g)
Hour 5: sports drink + caffeinated gel (45g + 25g)
Hour 6: cola and gel, easier on stomach

T2: Short rest — small gel, sip water, grab run fuel.

Run (3.5-6 hours):

First hour: 60g carbs/hour (gel every 20-30 min + aid station drink)
Middle: 30-45g carbs/hour, whatever you can keep down
Final 10km: cola, broth, simple sugars — focus on motion over nutrition

Salt on run: critical, especially in warm races. Salt tabs every 60-90 min, or salty aid station snacks.

Gut Training — The Prerequisite

You cannot fuel 90g/hour on race day if you've trained at 30g/hour. The gut needs progressive exposure.

Gut training protocol:

Weeks 1-3: target 40g/hour on long bike rides
Weeks 4-6: target 60g/hour
Weeks 7-9: target 80g/hour
Weeks 10+: target 90g/hour

Apply this on the bike. Run fuelling tolerance is genetically lower and has less trainable headroom.

Individual Sensitivities

People differ significantly in what their gut can handle. Things to track:

Sugar tolerance: some people cramp badly on fructose-heavy fuels. If gels hurt, try drinks.
Temperature sensitivity: warm drinks on cold days, cold drinks on warm days
Caffeine timing: some people respond to caffeine 30 min later, some immediately. Test in training.
Specific brands: Maurten vs SiS vs High5 all have different formulations. Try each, commit to what works.

Hydration — Match to Sweat Rate

Measure your sweat rate at least twice in training:

Weigh naked before a 60-90 min session
Don't drink during (or track fluid intake)
Weigh naked after
Weight lost + fluid intake = sweat rate per hour

Typical triathlete: 500-1200ml per hour. Some heavy sweaters: up to 2000ml per hour.

On race day, aim to drink 75-85% of your sweat rate — not 100%, as you'd be over-hydrating.

Post-Race Nutrition

Not glamorous, but matters for recovery:

Within 30 min: 30-40g protein + 60-80g carbs (recovery drink ideal)
Within 2 hours: full meal
Throughout the day: keep eating, keep drinking
Salt replacement: natural with most meals

Common Mistakes

Under-fuelling the bike. Most triathletes eat far less on the bike than they need, then blame the run for the poor performance that started much earlier.
New foods on race day. Your wetsuit isn't the only thing that needs testing in training.
Over-eating in T1/T2. You can't catch up on hours of under-fuelling with a quick gel. Steady is the game.
Ignoring sodium. In long races, sodium is often the limiting factor, not calories. Salty cramps = sodium, not fitness.

What's Next

Apply this to your goal race using the distance-specific plan. Combine with Brick Workouts to test your fuelling protocol under race-like conditions.

If you're building toward Full Ironman, see Full Ironman 20-Week Plan which incorporates nutrition progressions into the training plan.

The athletes who finish triathlons feeling good (not just finishing) are almost always the ones who got nutrition right. It's worth more than an extra 5% FTP.

Triathlon Nutrition Strategy🔒

Supporter content