When you run or walk for many hours in an ultramarathon, your body needs a steady supply of energy — mainly carbohydrate, plus some protein and fat — along with fluids and electrolytes. If you don't get that balance right, you risk bonking, gut issues, or being forced to slow dramatically.
What is CHO?
Throughout this guide, you'll see the term CHO, which stands for carbohydrate — the body's primary source of fast energy. During endurance events, CHO intake is measured in grams per hour (g/hr). Managing this intake carefully helps you stay fuelled without upsetting your stomach.
The Science Behind Ultra Fuelling
This article draws on the work of several leading sports nutritionists, including:
- Dr Asker Jeukendrup — Sports scientist, founder of Mysportscience.com, researcher into carbohydrate metabolism and endurance fuelling.
- Paul Booth — UK-based sports nutritionist specialising in endurance performance.
- Renee McGregor — Registered Sports & Eating Disorder Dietitian, author of Training Food and The Female Athlete.
- Nigel Mitchell — Performance nutritionist for Team Sky and British Cycling.
- International Society of Sports Nutrition (ISSN) — Authors of key position stands on endurance nutrition.
Key Takeaways from the Experts
- Train your gut — Regularly practice your race-day fuelling plan in training to increase your gut's ability to absorb carbohydrates efficiently.
- Use multiple carbohydrate sources — Combining glucose and fructose improves absorption and reduces stomach upset.
- Fuel consistently — Jeukendrup and Booth recommend 60–90 g CHO/hr, up to 120 g/hr for well-trained athletes.
- Add some protein and fat — McGregor and Mitchell highlight that small amounts of protein can reduce muscle damage.
- Hydrate smartly — Replace 400–800 ml of fluid per hour and 300–600 mg sodium every 60–90 minutes.
- Practice everything — Your body's response to food and drink is personal. Test all products in training.
THE LAP — Example Race Context
THE LAP is a 47-mile / 75km ultra trail race around Lake Windermere in the Lake District. The race features 5 fully stocked feed stations, 1 halfway drop bag station at Troutbeck, and food including water, cordial, electrolyte drink, Coke, energy bars and gels, salty snacks, and hot pizza at Troutbeck.
How Much to Eat and Drink
Below are practical guidelines for a 70kg athlete. Adjust for your size, pace, and weather conditions.
| Athlete Type | Typical Effort | CHO Target | Fluids |
|---|---|---|---|
| Fast runner | 6–8 min/km | 70–84 g CHO/hr | 500–800 ml/hr + electrolytes |
| Steady runner | Mix run/walk | 56–70 g CHO/hr | 400–700 ml/hr + electrolytes |
| Walker / slower pace | Mostly walking | 42–56 g CHO/hr | 400–600 ml/hr + electrolytes |
Example Hour-by-Hour Plan (Steady Runner)
- 0:00 – Start: Sip electrolyte drink (~25 g CHO)
- Every 30–45 min: Eat 20–30 g CHO (gel, chew, bar, or small real food)
- At Aid Stations: Refill bottles, take one CHO source (~20–30 g)
- Halfway (Troutbeck): Eat a small meal (pizza slice or savoury snack), refill bottles, adjust salt/electrolytes
- Final 10 miles: Increase small, frequent CHO doses as fatigue builds
Race-Day Tips
- Mix sweet and savoury to avoid flavour fatigue (Mitchell).
- Eat early — don't wait for hunger (Jeukendrup).
- Plan for weather — heat increases fluid needs.
- Watch your gut — if bloating, reduce intake briefly and sip water.
- Pack variety — quick carbs, solids, and comfort snacks for late race.
- Label your drop bag clearly for Troutbeck.
Hydration & Electrolyte Notes
- Fluids: 400–800 ml/hour
- Electrolytes: 300–600 mg sodium per hour
- Monitor: Cramping, bloating, or swelling → adjust intake
Summary
Fuelling an ultramarathon is about strategy, practice, and personal awareness, not guesswork. By following the science from Asker Jeukendrup, Paul Booth, Renee McGregor, and Nigel Mitchell, you can train your gut, manage hydration, and keep your energy steady across every mile of THE LAP — whether you're racing, jogging, or hiking to the finish.
References
- Jeukendrup, A. (Mysportscience). Fuelling for Endurance Sports.
- Booth, P. (2022). Endurance Nutrition Strategies. paulboothnutrition.com
- McGregor, R. (2019). Training Food. Bloomsbury Publishing.
- Mitchell, N. (2020). The Plant-Based Cyclist: A Nutrition Guide for Performance.
- International Society of Sports Nutrition. Position Stand: Nutritional Considerations for Endurance Athletes.