70.3 Nutrition Strategy: The Science and Practice of 60–90g Carbohydrates Per Hour

Introduction

70.3 race times typically range from 4.5 to 7 hours, with total caloric expenditure around 2500–3500 kcal. Research indicates that consuming 60–90g of carbohydrates per hour during exercise can maximize energy utilization and delay muscle glycogen depletion. But how does this number translate into actual fueling products? This article breaks it down step by step.

The Scientific Basis of Carbohydrate Absorption Limits

• Glucose alone: intestinal transport protein SGLT1 has an upper limit of approximately 60g/hr
• Glucose + fructose (2:1 or 1:0.8): can reach 90g/hr, as fructose uses the GLUT5 pathway
• 90g/hr typically requires gut training to adapt; never attempt it for the first time on race day

Fueling Plan by Discipline

Practical Example: Male with FTP 220W

• Bike: 3 gels of 25g each + 2 bottles of 600mL sports drink (40g carbs each) = approx. 155g carbs (approx. 60g/hr)
• Advanced: add 1 high-concentration gel (45g carbs) to reach 80g/hr
• Run: 3 gels of 25g each + 1 can of cola (200mL, approx. 22g carbs) = approx. 97g carbs (approx. 45g/hr)

Glucose-to-Fructose Ratio Recommendations

• 60g/hr: pure glucose is sufficient
• 75g/hr: glucose-to-fructose ratio = 2:1
• 90g/hr: glucose-to-fructose ratio = 1:0.8 (high-efficiency formula)

Progressive Gut Training Strategy

1. W1–W4: try 40g/hr during each long session
2. W5–W8: increase to 60g/hr
3. W9–W12: try 75–80g/hr
4. W13+: simulate 90g/hr to observe gut response

Practical Tips

• Never use untested fueling products on race day
• The bike is the primary fueling window; eat up before starting the run
• On the run, liquid fuel (cola, sports drink) is easier to absorb
• In hot conditions, reduce solid food ratio and increase fluids and electrolytes

Conclusion

70.3 is not simply a “calorie expenditure race,” but a “fuel management race.” The 60–90g of carbohydrates per hour is an evidence-based safe range. Train your gut to accept this range during the training period so that on race day you can fully cash in on your training efforts.

Related Reading

• The Science of In-Race Fueling: How Many Carbs Per Hour? A Complete Practical Guide from 60g to 90g
• Training Fueling Strategies: How to Achieve 60–90g of Carbs Per Hour
• IRONMAN Fueling: Gut Training for 90–120g of Carbs Per Hour
• 90 or 120 Grams of Carbs Per Hour on Race Day? Interpreting the Latest Intake Limits