Nutrition is the fourth discipline of triathlon, and in a 70.3, it's the discipline that determines whether your run is strong or a survival march. The physiological reality is simple: your body stores roughly 90-120 minutes of glycogen at race intensity. A 70.3 takes 4-7 hours. If you don't eat enough, you will run out of fuel before the finish line.
This guide gives you an hour-by-hour nutrition timeline for a typical 70.3 race, with specific targets for carbohydrates, sodium, hydration, and caffeine.
The Numbers You Need to Know
Before building a timeline, you need four numbers:
| Nutrient | Bike Target (per hour) | Run Target (per hour) |
|---|---|---|
| Carbohydrates | 60-80g | 30-60g |
| Sodium | 500-700mg (700-1000mg in heat) | 400-600mg |
| Fluid | 500-750ml | 400-600ml |
| Caffeine | 150-200mg total (1-2 doses) | 50-100mg (optional) |
These ranges are based on current sports science consensus and have been validated across hundreds of thousands of race performances. Individual variation exists — which is why you practice in training — but these ranges cover the majority of age-group athletes.
Hour-by-Hour Timeline (for a ~5:30 Total Race)
Pre-Race (2-3 hours before start)
- 100-150g carbs: bagel with jam, white rice with honey, or oatmeal with banana
- 300-500ml water or sports drink
- 500-700mg sodium (preload)
- Optional: 100mg caffeine (if you're a regular caffeine user)
- Avoid: high fiber, high fat, dairy, anything untested
Swim (~30-35 minutes): No nutrition needed
Your pre-race breakfast and glycogen stores handle the swim. Focus on effort and execution.
T1 (2-4 minutes): Nothing
Don't eat in transition. Get on the bike and settle in.
Bike Hour 1 (km 0-30)
- Start eating within 15 minutes of mounting the bike. Don't wait.
- 60-80g carbs: 2 gels (40-50g) + sports drink (20-30g), or a bar + drink mix
- 500-700mg sodium: from gels, drink mix, or electrolyte capsules
- 500-600ml fluid
- Reminder at 15min and 20min intervals on your bike computer
This hour feels easy. You're fresh, the effort is moderate, and you won't feel hungry. Eat anyway. What you consume now fuels your run 3 hours from now.
Bike Hour 2 (km 30-60)
- 60-80g carbs: same pattern as hour 1
- 500-700mg sodium
- 500-700ml fluid (increase if sweating heavily)
- Caffeine dose: 150-200mg at the 45-60 minute mark of the bike (a caffeinated gel or caffeine tablet). This peaks in your bloodstream at approximately the right time for the run.
By mid-bike, your effort has settled into a rhythm. Eating should be mechanical at this point — set the timer, eat when it beeps, don't think about it.
Bike Hour 3 / Final 30km (km 60-90)
- 60-80g carbs
- 500-700mg sodium
- 500-700ml fluid
- Last solid food before km 75. Switch to liquids and gels only in the final 15km so your stomach has time to process before the run.
- Optional second caffeine dose (75-100mg) if your race will exceed 5.5 hours total.
The critical transition: in the final 10km of the bike, take one gel with water. This is your run-start fuel. It needs 15-20 minutes to absorb, and you want it hitting your bloodstream as you start running.
T2 (2-3 minutes)
- One sip of sports drink or a few swallows of water as you leave transition
- Take one gel with you if you don't have a run belt with nutrition
Run Hour 1 (km 0-7)
- 30-50g carbs per hour: gels, cola at aid stations, or sports drink
- 400-600mg sodium: electrolyte capsules or salty foods at aid stations
- 400-500ml fluid: drink at every aid station, don't skip any
- Walk through the first aid station. Seriously. 15 seconds of walking to drink properly saves you from minutes of GI distress later.
Your gut is now compromised. You've been exercising for 3.5+ hours and the mechanical jostling of running reduces gastric emptying. Liquid calories (cola, sports drink) are often better tolerated than gels on the run. If gels make you nauseous, switch to cola and pretzels at aid stations.
Run Hour 2 (km 7-15)
- 30-50g carbs per hour
- 400-600mg sodium
- 400-600ml fluid
- If nauseous: slow down slightly (10-15 seconds per km), take small sips instead of big gulps, and switch to cola. Walking for 60 seconds often lets your gut reset.
This is the critical hour. Athletes who under-fueled on the bike begin bonking here. If you followed the bike nutrition plan, you should be running on relatively full glycogen stores.
Run Hour 3 / Final 6km (km 15-21.1)
- Maintain fluid and sodium at aid stations
- Carb intake becomes optional — you're running on willpower and whatever fuel is already absorbed
- Cola at the last few aid stations provides a quick sugar and caffeine hit
- Give everything you have left
What Products Actually Work
The specific product matters far less than the practice. That said, here are the categories that work well for 70.3 racing:
Gels (25-30g carbs each): The most portable, most reliable option. Isotonic gels (that don't need water) are easier to take while riding. Take with a small sip of water regardless.
Drink mix (30-50g carbs per bottle): Combines hydration and calories. The simplest approach is a concentrated drink mix in your aero bottle and plain water in your frame bottles.
Bars/chews (20-40g carbs per serving): Good for the first half of the bike when your stomach is calm. Harder to eat later as fatigue sets in. Cut bars into small pieces the night before.
Cola (27g carbs per 250ml): Best on the run. Provides sugar, caffeine, and psychological relief from gel fatigue. Ask for flat cola at aid stations if available.
Electrolyte capsules (200-250mg sodium each): The easiest way to hit sodium targets independently of your carb strategy. Take 2-3 per hour.
The Gut Training Principle
Your gut is trainable. The enzymes that transport carbohydrates from your intestine to your bloodstream (SGLT1 for glucose, GLUT5 for fructose) upregulate with consistent training. An athlete who practices eating 80g/hr in training will absorb 80g/hr in racing. An athlete who never eats during training will struggle to absorb 40g/hr on race day.
Start practicing race nutrition 8-10 weeks before your race. In every workout longer than 90 minutes, eat at your target race rate. Your gut will adapt.
Hot Weather Adjustments
Heat changes everything about nutrition.
Above 25°C (77°F), your body diverts blood to your skin for cooling, away from your gut. Absorption efficiency drops. Sweat rate increases, depleting both fluid and sodium faster.
The adjustments:
- Increase sodium by 200-300mg per hour (800-1000mg total)
- Increase fluid by 200-300ml per hour (700-1000ml total on the bike)
- Consider reducing carb target by 10-15% if experiencing GI distress — it's better to eat slightly less than to vomit
- Use ice in your hat and trisuit to manage core temperature — this isn't nutrition, but it enables better nutrition by keeping your gut functional
Build Your Personalized Nutrition Plan
Your body weight, race distance, course conditions, and weather all change the exact numbers. RaceDayAI calculates your specific nutrition targets and builds a gel-by-gel, aid-station-by-aid-station timeline for your race.
← Back to The Complete 70.3 Race Execution Guide
Last updated: March 2026