How to Fuel for a Half marathon

Learning how to fuel for a half marathon correctly can make the difference between cruising across the finish line with a smile or hitting the dreaded "wall" at mile 10. While training your legs to cover 13.1 miles is crucial, training your stomach is equally important. Carbohydrates act as your body’s primary high-octane fuel, stored in your muscles and liver as glycogen. Because your body can only store enough glycogen for about 90 to 120 minutes of vigorous exercise, a structured half marathon nutrition strategy ensures your energy levels remain stable from start to finish.

Whether you are working with Nutrition and Co to fine-tune your performance or tackling your first race independently, this evidence-based guide breaks down the exact nutrition protocols you need before, during, and after your 13.1-mile run.

The Physiology of Endurance Fueling

When running at a moderate to high intensity, your body relies predominantly on carbohydrates because they yield energy faster per unit of oxygen than fats.  

• Glycogen Depletion: Your body stores approximately 400 to 500 grams of carbohydrates as glycogen. Without active replenishment, these stores empty within 75 to 90 minutes of sustained running.

• Gastric Emptying Rate: During exercise, blood flow shifts away from the digestive tract toward active muscles. Consuming simple carbohydrates that require minimal digestion prevents gastrointestinal (GI) distress.  

• Electrolyte Balance: Sodium lost through sweat must be replaced to maintain muscle contraction dynamics and plasma volume. You can read more about managing fluid loss in the official Gatorade Sports Science Institute Research.

Pre-Race Fueling: Days Before and Race Morning

Carbohydrate Loading (24 to 48 Hours Before)

Unlike a full marathon, which requires a 3 to 4-day carb-loading phase, a half marathon requires a focused 24 to 36-hour emphasis on high-carbohydrate meals. To avoid common fueling mistakes, check out the guide on Common Sports Nutrition Mistakes.  

• Target: 7 to 10 grams of carbohydrate per kilogram of body weight per day.

• Food Selection: Choose low-fibre, easily digestible carbohydrates to maximise glycogen stores without causing bloating.  

• Ideal Choices: White rice, pasta, bagels, oats, bananas, and fruit juices.  

• Limit: High-fat meals, spicy foods, and excess dietary fibre.

The Race Day Breakfast (2 to 4 Hours Prior)

Your goal on race morning is to top off liver glycogen stores depleted overnight during sleep.

Timeframe	Recommended Meal	Carbohydrate Target
3–4 Hours Before	Large plain bagel with honey + banana + 500ml water	1.5-2.0 g/kg body weight
2 Hours Before	Oatmeal cooked in water with maple syrup + sports drink	1.0 g/kg body weight
30–45 mins before	Single energy gel or small energy chew + 200ml water	20-30 grams

Mid-Race Nutrition: During the half marathon

Once you cross the start line, fueling shifts to maintaining circulating blood glucose levels and delaying muscle fatigue.

Carbohydrate Intake Guidelines

If you expect to finish the race in under 75 minutes, plain water and a pre-race gel are typically sufficient. However, for most runners finishing between 75 minutes and 2.5 hours, active mid-race fueling is required.

• Target Rate: 30 to 60 grams of carbohydrate per hour.

• Timing: Begin taking energy gels or chews early—around minute 30 to 45, rather than waiting until you feel exhausted.  

• Gel Strategy: Consume one standard energy gel (containing 20–25g carbs) every 30 to 45 minutes, always accompanied by small sips of plain water to accelerate absorption. For guidance on customised endurance strategies, read about Endurance Fueling Frameworks

Hydration and Electrolytes

Fluid loss exceeding 2% of total body weight can significantly impair physical performance and elevate heart rate.

• Fluid Rate: Aim for 400 to 800 ml of fluid per hour, adjusted for sweat rate, temperature, and humidity.  

• Sodium Intake: Aim for 300 to 600 mg of sodium per hour, particularly on warm days or for heavy sweat rates, using electrolyte beverages or salt tabs. Review the ISSN Position Stand on Exercise & Sports Nutrition for detailed nutrient intake guidelines.

Post-Race Recovery: Rebuilding and Refuelling

The post-race window is critical for initiating muscle tissue repair and restocking depleted glycogen stores. For tailored 1-on-1 performance strategies, you can consult a qualified specialist via Nutrition and Co Sports Dietitians.  

Post-Race Recovery Priority Sequence:

  [0 - 45 Minutes] ──> Consume 3:1 Carb-to-Protein Snack (e.g., Chocolate Milk)
        │
        ▼
  [1 - 2 Hours]   ──> Eat a Balanced Meal (Carbs + Lean Protein + Healthy Fats)
        │
        ▼
  [Rest of Day]   ──> Rehydrate to 150% of Fluid Lost via Sweat

1. Refuel Glycogen: Consume 1.0 to 1.2 grams of carbohydrate per kilogram of body weight within 45 minutes of finishing.

2. Repair Muscle: Pair your carbohydrates with 20 to 30 grams of high-quality protein to stimulate muscle protein synthesis.

3. Rehydrate: Drink 1.5 litres of fluid for every kilogram of body weight lost during the run.

4. External Resource: For official international dietary reference intakes and carbohydrate guidelines for endurance performance, refer to the Academy of Nutrition and Dietetics / ACSM Guidelines.

Frequently Asked Questions

Do I really need energy gels for a half marathon?

If your estimated finish time exceeds 75 to 90 minutes, energy gels or alternative simple carbohydrate sources (like sports drinks or chews) are highly recommended. They provide rapid-acting glucose to maintain race pace and delay central nervous system fatigue.  

How do I train my gut to avoid stomach upset on race day?

Gut training involves practising your exact race day fueling protocol during long training runs. Consume energy gels and fluids at race pace at least 4 to 6 weeks leading up to the event to allow the intestinal tract to upregulate carbohydrate transport proteins.

Should I drink water or a sports drink at aid stations?

A combination works best. Use sports drinks to contribute toward your hourly carbohydrate and electrolyte goals. If you are consuming concentrated energy gels, always wash them down with plain water to prevent delayed gastric emptying and abdominal cramping.  

If you would like specific advice on how to meet your performance goals, book an initial appointment with our team today.