Triathlon Nutrition Rules of Thumb — Carbs, Fluids & Electrolytes
The key numbers every triathlete needs: how many carbs per hour, how much to drink, how much sodium to take, and when to fuel across each discipline. These evidence-based guidelines apply to Sprint through Ironman racing.
Carbohydrate Intake by Race Duration
Carbohydrate needs scale with race duration, not distance. The longer you race, the more you need per hour — up to a ceiling set by gut absorption limits.
| Race duration | Carbs/hour | Typical format | Notes |
|---|---|---|---|
| Under 60 min | 0–30g/hr | Super Sprint | Water only is usually sufficient |
| 1–2.5 hours | 30–60g/hr | Sprint, fast Olympic | Single carb source works fine |
| 2.5–5 hours | 60–90g/hr | Olympic, Half Ironman | Mix glucose + fructose sources |
| 5+ hours | 90–120g/hr | Full Ironman | Requires gut training; 2:1 glucose:fructose ratio |
Why the glucose:fructose ratio matters at high intake
The gut absorbs glucose and fructose via separate transporters. Using only glucose caps absorption at ~60g/hr. Adding fructose (2:1 glucose:fructose) allows 90–120g/hr. Products like Maurten, Science in Sport Beta Fuel, and Precision Hydration use this principle.
Fluid Intake Guidelines
Hydration needs vary significantly based on sweat rate, temperature, humidity, and effort level. The ranges below are starting points — use the Sweat Rate Calculator to personalise.
| Condition | Fluid/hour | Notes |
|---|---|---|
| Cool conditions (<15°C / 59°F) | 400–600ml / 14–20oz | Lower sweat rates; don't over-drink |
| Moderate (15–25°C / 59–77°F) | 600–800ml / 20–27oz | Standard baseline for most races |
| Hot conditions (>25°C / 77°F) | 800ml–1L / 27–34oz | Must include electrolytes at this rate |
| High sweat rate athletes | Up to 1.5L / 50oz | Check with sweat rate test; replace 80% of losses |
Over-drinking is a real risk
Hyponatremia (low blood sodium from drinking too much plain water) causes more hospitalisations at Ironman events than dehydration. Drink to thirst, not to a rigid schedule, and always include sodium in your fluids.
Electrolyte Guidelines
Sodium is the most important electrolyte for endurance athletes. Potassium, magnesium, and calcium matter less during racing but support training recovery.
| Electrolyte | Target (per hour racing) | What it does | Deficiency signs |
|---|---|---|---|
| Sodium | 500–1,000mg/hr | Fluid retention, nerve function | Cramping, nausea, confusion |
| Potassium | 150–300mg/hr | Muscle contraction | Muscle weakness, cramping |
| Magnesium | 20–40mg/hr | Energy metabolism, relaxation | Cramps, fatigue |
Use the Electrolyte Calculator for personalised targets based on your sweat rate and race duration.
Pre-Race Nutrition Timing
| Time before race | What to eat/drink | Why |
|---|---|---|
| Night before | High-carb dinner, 2–2.5g carbs/kg body weight throughout the day | Top up glycogen stores |
| 3–4 hours before | 400–600 calories: oats, toast, banana, low-fat/fibre | Full pre-race meal with digestion time |
| 60–90 min before | 500ml electrolyte drink, small snack if needed | Pre-load hydration and sodium |
| 30–45 min before | Caffeine (3–6mg/kg) if using it | Peak plasma concentration at race start |
| 5–10 min before | Small gel or 20–30g carbs | Top up blood glucose just before start |
Nutrition by Discipline: Swim, Bike, Run
Swim
No nutrition during the swim. The effort, horizontal position, and water make eating impractical and dangerous. If your race is short (<30 min swim), this is not a concern. For longer swims, make sure you're well-fuelled beforehand and have a plan for what to take immediately after exiting the water.
Bike
The bike leg is your primary fuelling window. The lower GI stress of cycling (vs running) allows you to absorb carbs, fluids, and electrolytes most efficiently. Take your first nutrition within the first 20–30 minutes of the bike leg — don't wait until you feel hungry or thirsty.
Aim to consume 60–90% of your total race nutrition on the bike. Eat and drink every 15–20 minutes on a schedule, not on impulse.
Run
GI stress peaks during the run. Stick to liquid or semi-liquid carbs (gels, sports drinks) rather than solid food. Caffeine gels in the second half of a long run can help with fatigue. At aid stations, take walk breaks to ensure you actually absorb the fluid — running through while drinking often means choking half of it.
Post-Race Recovery Nutrition
The 30-minute window after finishing is critical for glycogen replenishment and muscle repair:
- Carbs: 1–1.2g per kg body weight (e.g., 70–84g for a 70kg athlete)
- Protein: 20–30g to stimulate muscle protein synthesis
- Fluid: 150% of fluid lost during the race (weigh before and after to calculate)
- Sodium: Include electrolytes in your recovery fluid to aid retention
Chocolate milk, recovery shakes, and rice with chicken are all effective options. Don't skip the recovery window because you feel okay — muscle damage continues for hours after finishing.
These guidelines are evidence-based starting points. Your individual sweat rate, gut tolerance, and race conditions require personalisation. Use the calculators on this site to build your specific plan, then test every element in training before race day. Never try new nutrition products on race day.
Try a calculator
- Race Nutrition Planner
Apply these rules to your race in a single calculator.
- Carb Timing Calculator
Plan exact gel timing without doing the math.
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