Nutrition Basics for Marathon and Ultra Runners

Proper nutrition can make or break your marathon or ultra performance. You can have the fitness to run a personal best, but if your fuelling strategy fails, you'll find yourself walking when you should be running. Conversely, dialling in your nutrition allows you to access all the fitness you've built and perform to your potential.

This guide covers the fundamental principles of endurance running nutrition, from understanding your energy systems to developing a practical race-day fuelling plan.

Understanding Energy Systems

Your body has two primary fuel sources during running: glycogen (stored carbohydrates) and fat. Understanding how these work together is crucial for effective fuelling.

Glycogen is stored in your muscles and liver. It's your body's preferred fuel for moderate to high-intensity exercise because it can be converted to energy quickly. However, storage capacity is limited—most runners can store enough glycogen for about 90-120 minutes of running at marathon pace.

Fat provides a virtually unlimited fuel source (even lean runners have tens of thousands of calories stored as fat), but it can only be metabolised relatively slowly. At higher intensities, fat simply can't provide energy fast enough to meet demand.

During long distance running, you use both fuels simultaneously, with the ratio depending on intensity. At easier paces, fat contributes more; at harder efforts, you rely more heavily on glycogen. When glycogen runs low—the infamous "bonk" or "hitting the wall"—you're forced to slow dramatically because you're limited to what fat metabolism can provide.

The Role of Carbohydrates

For marathon and ultra runners, carbohydrates are king. While there's been interest in low-carb approaches, the scientific evidence overwhelmingly supports carbohydrate availability for optimal endurance performance.

Carbohydrate Loading

In the 2-3 days before a long race, increasing carbohydrate intake helps maximise glycogen stores. This doesn't mean eating mountains of pasta—it's more about shifting the proportion of calories toward carbohydrates while moderating total intake as you taper training.

Aim for 8-10 grams of carbohydrate per kilogram of body weight daily during this loading phase. A 70kg runner would target 560-700g of carbohydrate per day. Choose familiar, easily digested foods—race week isn't the time to experiment with new cuisines.

Fuelling During Running

For runs under 60-75 minutes, you generally don't need to consume calories—your glycogen stores are sufficient. But for marathons and ultras, taking in fuel during the event is essential.

How Much to Consume

Current guidelines suggest 30-90 grams of carbohydrate per hour during endurance events, depending on duration and intensity:

• Marathon (2.5-4 hours): 30-60g per hour
• 50km Ultra (4-7 hours): 40-70g per hour
• 100km+ Ultra (8+ hours): 60-90g per hour

The higher end of these ranges requires training your gut to tolerate more fuel, and using carbohydrate sources that utilise multiple transport pathways (glucose/maltodextrin plus fructose). Start conservatively and build up through training.

Timing Your Fuel

Rather than waiting until you feel depleted, start fuelling early and maintain consistent intake throughout. For most runners, consuming something every 20-30 minutes works well. Set a timer or use distance markers as reminders.

Begin fuelling within the first 45-60 minutes—even though you don't need it yet, establishing the pattern early ensures you don't fall behind. By the time you feel low on energy, it's already too late to fully recover during the race.

Managing Stomach Issues

Gastrointestinal distress is one of the most common problems in long distance running. Blood diverts away from your digestive system during exercise, making digestion more difficult. Heat, dehydration, and anxiety exacerbate the problem.

Prevention Strategies

• Train your gut: Practice race nutrition during training to adapt your digestive system
• Reduce fibre: Lower fibre intake for 24-48 hours before racing
• Stay hydrated: Dehydration significantly increases GI issues
• Avoid fat and protein: These slow digestion and increase stomach distress during running
• Use familiar products: Never try new nutrition on race day
• Small, frequent intake: Smaller amounts more often is easier than large amounts occasionally

Ultra-Specific Nutrition

Ultramarathons present unique nutritional challenges. As events extend beyond 4-5 hours, several additional factors come into play.

Palate Fatigue

Sweet gels and drinks that taste fine for a marathon become nauseating after many hours. Ultra runners typically need variety—savoury options like sandwiches, chips, broth, and pickles become appealing as the event progresses. Plan for this by including savoury options in your nutrition strategy.

Real Food

In very long events, real food becomes not just tolerable but often preferable to engineered products. The slower pace of ultras allows more time for digestion. Popular ultra foods include:

• Boiled potatoes (with salt)
• PB&J or Vegemite sandwiches
• Bananas
• Watermelon
• Pretzels or chips
• Soup or broth
• Avocado on toast

Protein Considerations

For events lasting 10+ hours, some protein intake may help preserve muscle and reduce perceived fatigue. Small amounts from real food are generally sufficient—you're not trying to build muscle during the race, just maintain blood amino acid levels.

Caffeine as a Performance Aid

Caffeine is one of the most researched and effective legal performance enhancers for endurance sports. It reduces perceived effort, enhances fat oxidation, and improves mental alertness—all valuable during long races.

Effective doses range from 3-6mg per kilogram of body weight. A 70kg runner might aim for 200-400mg. Many runners save caffeine for the latter stages of races when fatigue accumulates, using caffeinated gels, cola, or caffeine tablets.

If you don't regularly consume caffeine, test your tolerance during training. Some individuals are more sensitive and may experience jitteriness, GI upset, or anxiety.

Developing Your Personal Plan

Generic guidelines provide a starting point, but effective race nutrition is highly individual. Use training runs to test and refine your approach:

1. Calculate your target: Start with 40-50g carbs per hour for marathons
2. Choose your products: Select gels, chews, or drinks that appeal to you
3. Create a schedule: Plan what you'll consume and when
4. Test in training: Use long runs to practice your exact race-day plan
5. Refine based on results: Adjust quantities, timing, and products based on how your body responds
6. Consider conditions: Hot weather may require more liquid calories; cool weather might allow more solid food

Race Day Execution

Once you've developed a plan that works in training, execute it consistently on race day:

• Lay out all your nutrition the night before
• Have a backup plan in case aid stations don't have what you expected
• Set watch alarms or use distance markers to remind yourself to fuel
• Don't get swept up in race excitement and forget to eat
• If your stomach is unhappy, slow down rather than stopping nutrition entirely
• Stay flexible—sometimes conditions or how you feel require adaptation

Nutrition is often called the "fourth discipline" of endurance sports (after swim, bike, run in triathlon—or just good execution alongside training and mental toughness for runners). Invest time in developing your strategy, practice it thoroughly, and you'll arrive at the finish line having accessed all the fitness your training has built.