What to eat before a half Ironman isn't just about race morning - it's about the 48 hours leading up to the start line. The 70.3 distance (1.9km swim, 90km bike, 21.1km run) demands 4.5 to 8.5 hours of continuous effort. Your nutrition strategy needs to match that scale.
The Challenge: 70.3 Miles of Continuous Effort
Your body stores roughly 500g of carbohydrate as glycogen - about 2,000 calories. That's enough for maybe 3 hours of steady effort. A half Ironman takes most athletes 4.5-8.5 hours. The maths doesn't work unless you nail both your carb loading and your race-day fuelling. This is why half Ironman nutrition starts days before the race, not hours.
Carb Loading: 36-48 Hours Before Race Day
For a Sunday race, start Friday afternoon. Research recommends 7-10g of carbohydrate per kg of bodyweight daily during this period.
For a 70kg athlete, that's 490-700g of carbs per day. This isn't about one big pasta dinner - it's sustained, deliberate carb intake across two days.
This fills your glycogen stores completely, giving you the maximum fuel tank to start with.
The 48-Hour Countdown
Friday (2 Days Before)
Start increasing carb intake. Choose familiar, easily digestible sources - rice, pasta, bread, potatoes, cereals. Reduce fibre intake to minimise GI issues on race day. Keep protein moderate, fat low. Stay hydrated but don't overdo it.
Saturday (Day Before)
Continue carb loading. Eat your last large meal at lunch or early dinner - nothing new, nothing adventurous. Evening meal should be moderate and early. Avoid high-fibre vegetables, beans, and foods that cause you bloating. Hydrate consistently but not excessively.
Saturday Evening
Early dinner (5-6pm for a Sunday morning race). Keep it simple: pasta with tomato sauce, rice with chicken, sandwich - whatever you know sits well. Avoid alcohol completely. Get everything ready for race morning so you can relax.
Race Morning: The Final Hours
3-4 Hours Before Start
- Wake early: Give yourself time to eat and digest without rushing
- Pre-race meal: 1-2g carbs per kg bodyweight (70-140g for 70kg athlete)
- Keep it familiar: Porridge, toast with jam, bagel, banana - whatever you've practised
- Low fat, low fibre: Quick digestion is the priority
- Hydrate: 500ml water or sports drink, sip don't gulp
2 Hours Before
Finish eating main food by this point. Continue sipping water or sports drink. Use the toilet - you want everything processed before you're in a wetsuit. Light movement, final preparations.
30-60 Minutes Before
Small top-up if needed - dates, natural energy gel, or sports drink, half a banana. Nothing that needs digesting. Final hydration but don't overdo it - starting the swim with a full bladder is uncomfortable.
15 Minutes Before
Final sips of water only. Focus shifts from nutrition to race execution. Trust your preparation.
Best Pre-Race Foods
Carb Loading Phase (Friday-Saturday)
- White rice - Easy to digest, high carb density
- Pasta with simple sauces - Classic for good reason
- White bread, bagels, rolls - Low fibre, high carb
- Potatoes (without skin) - Versatile, easy to eat in volume
- Cereals with low-fat milk - Quick breakfast option
- Pancakes or waffles - With maple syrup, not heavy toppings
- Rice cakes, crackers - Easy snacking between meals
- Fruit juice, sports drinks - Liquid carbs help hit targets
Race Morning Breakfast Ideas
- Porridge with honey and banana - Sustained energy, easy on stomach
- Toast with jam or honey - Simple, quick digesting
- Bagel with peanut butter - If eaten 3+ hours before
- Rice with a little soy sauce - Some athletes prefer savoury
- Overnight oats (made simple) - Prepared night before
- Commercial pre-race products - If you've tested them in training
The GI Issue Reality
30-70% of Athletes Experience GI Problems
A significant percentage of half Ironman athletes experience gastrointestinal issues during the race - from mild discomfort to performance-ending problems. Most GI distress comes from nutritional mistakes: eating too close to race start, trying new foods, too much fibre, or overdrinking. Everything you eat race week should be tested in training first.
What to Avoid Pre-Race
- High-fibre foods - Whole grains, beans, high-fibre cereals during carb load phase
- New foods - Nothing you haven't tested in training
- Heavy, fatty meals - Slow digestion, sits heavy
- Alcohol - Impairs glycogen storage and hydration
- Spicy foods - Risk of GI distress during race
- Large protein portions - Slows digestion, not the priority
- Excessive caffeine - Save it for race day strategy
- Gas-producing foods - Cabbage, broccoli, onions, beans
Hydration Strategy
Hydration during carb loading is about consistency, not excess:
- Friday-Saturday: Drink to thirst plus a bit more - stay well hydrated
- Don't overdrink: Hyponatraemia (low blood sodium) from overdrinking is a real race risk
- Include electrolytes: Some sodium in your pre-race drinks helps fluid retention
- Race morning: 500ml with breakfast, then sip as needed
- Stop drinking large volumes: 30-60 minutes before swim start
Race Day Fuelling Plan
Pre-race nutrition sets you up, but you'll need to fuel during the race too:
- Target: 60-90g carbs per hour during bike and run (some athletes tolerate up to 120g/hr)
- Bike leg: Easiest time to eat - use natural energy bars, dates or natural gels, sports drinks
- Run leg: Harder to digest - rely more on natural gels and liquids
- Practice in training: Your gut needs to be trained to handle race-day nutrition
Evidence-Based Pre-Half Ironman Summary
- Carb loading: 7-10g/kg/day for 36-48 hours pre-race
- Race morning: 1-2g/kg carbs 3-4 hours before start
- GI issues affect 30-70% of athletes - only eat tested foods
- Low fibre, low fat: Prioritise quick digestion during race week
- Hydrate consistently but don't overdrink
- During race: Target 60-90g carbs/hour (bike especially)
- Nothing new: Every food and product should be tested in training first
Crossed the finish line? See our guide on what to eat after a half Ironman.
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