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Ultramarathons, races that exceed the standard marathon distance of 26.2 miles, are gruelling tests of endurance, mental fortitude, and physical resilience. Whether you’re tackling a 50K, 100K, or 100-mile race, one of the most critical factors determining your success is your nutrition strategy. Proper fuelling will power your muscles and your brain and could be the difference between crossing the finish line or facing a dreaded DNF.
In this article, I’ll cover evidence-based strategies for ultramarathon nutrition, exploring the best practices for carbohydrate, fat, and protein intake, hydration, electrolyte balance, and timing to optimise your performance on race day.
Carbohydrates are the primary fuel source for endurance athletes, including ultramarathoners. The body’s glycogen stores, found in muscles and the liver, provide a readily available source of energy during prolonged exercise. However, these stores are limited and will become depleted within a few hours of activity, leading to fatigue, reduced performance, and the dreaded “bonk” or “hitting the wall.”
Research indicates that a high carbohydrate intake is a crucial element for ultramarathon nutrition. A study examining the nutrition habits of elite ultramarathoners found that these athletes consumed an average of 71 grams of carbohydrates per hour during races, aligning with contemporary recommendations of 40 to 110 grams per hour1,2, depending on the duration and intensity of the exercise. This high carbohydrate intake helps sustain glycogen levels, delay fatigue, and improve overall endurance.
For ultramarathoners, it is recommended to:
Carbohydrate Load Pre-Race: In the days leading up to the race, increase your carbohydrate intake to 8-12 grams per kilogram of body weight per day to maximise glycogen stores. This ensures that your muscles are fully stocked with glycogen, giving you a more substantial energy reserve to draw from during the race. It’s important to taper your training while increasing your carb intake to avoid burning through your glycogen stores before race day.
During the Race: Aim to consume 60-110 grams of carbohydrates per hour. Please note that intakes of 90+g/h can be pretty difficult to achieve without considerable practice. Whilst these higher intakes might offer a small benefit don’t rush straight to them, your digestive system will thank you. Your carbs for the race can be a combination of sports drinks, gels, chews, and easily digestible solid foods like bananas, energy bars, or rice cakes. The timing of carbohydrate intake is crucial, starting early and maintaining consistent fuelling throughout the race helps to maintain stable blood sugar levels and prevent the onset of fatigue.
Use multiple transportable carbohydrates: Multiple transportable carbohydrates refer to combinations of sugars, usually glucose and fructose, that are absorbed through different pathways in the digestive system, allowing for higher rates of carbohydrate absorption and oxidation. The body typically can absorb only a certain amount of glucose, usually up to about 60 grams per hour. Any more than this and you are risking a digestive disaster. Consuming multiple transportable carbohydrates will increase the body’s capacity to absorb more carbohydrates. By using products that combine glucose/maltodextrin and fructose, such as certain sports drinks, gels, foods and chews, ultramarathoners can sustain higher energy levels, delay fatigue, and maintain performance over long distances.
Post-Race Recovery: After the race, your glycogen stores will be depleted. It’s important to replenish them quickly to kickstart recovery. Consuming a high-carbohydrate meal or snack within 30 minutes post-race can help restore glycogen levels and speed up muscle repair. General guidelines are to aim for 1.0-1.2 grams of carbohydrates per kilogram of body weight immediately after finishing the race, followed by regular carbohydrate-rich meals in the following 24 hours. This means that as you begin to face plant the nearest baked goods you can do so safe in the knowledge that this is a great strategy to start your recovery.
While carbohydrates are the primary fuel during high-intensity efforts, fats also play a significant role in ultra-endurance events. Some ultrarunners adopt a low-carbohydrate, high-fat (LCHF) or ketogenic diet to increase their body’s ability to oxidise fat, theoretically sparing glycogen and enhancing endurance.
The evidence supporting fat adaptation for ultramarathon performance is mixed. Studies have shown that while fat-adapted athletes can indeed increase their fat oxidation, this often comes at the expense of reduced carbohydrate metabolism, which is critical for maintaining higher intensities during a race3. The efficiency of fat oxidation, while useful at lower intensities, does not match the rapid energy demands required during high-intensity sections of a race, such as uphill climbs or when trying to maintain pace in the later stages.
The empirical evidence supporting the performance-enhancing claims of ketogenic diets in ultramarathons is sparse, with most successful athletes opting for a ultramarathon nutrition plan that prioritises carbohydrate availability.
While carbohydrates and fats are the primary energy sources during an ultramarathon, protein plays a crucial role in muscle repair and recovery. During prolonged exercise, some muscle protein breakdown occurs, and adequate protein intake helps minimise this damage and speeds up recovery post-race.
During the Race: Although protein is not a primary fuel source during the race, consuming small amounts (around 5-10 grams per hour) may help reduce muscle damage. This can be achieved through protein-enhanced sports drinks, bars, or small amounts of real food like nuts or cheese.
Post-Race: After the race, focus on consuming 0.4g/kg bodyweight (for most people that’s around 20-30 grams) of high-quality protein within 30-60 minutes to kickstart muscle repair.
Proper hydration is critical for maintaining performance and preventing heat-related illnesses, so it needs to be a cornerstone of any ultramarathon nutrition plan. However, hydration needs are highly individual and can vary based on factors such as body size, sweat rate, and environmental conditions.
Pre-Race: Begin your race well-hydrated by drinking plenty of fluids leading up to the event. Monitor the colour of your urine – pale yellow is a good indicator of adequate hydration.
During the Race: Aim to drink small amounts frequently, rather than large quantities at once, to avoid gastrointestinal distress. A good starting point is 400-800 millilitres per hour, adjusting based on thirst and weather conditions. Be mindful that you can overhydrate, which can lead to hyponatremia, which is a dangerous drop in blood sodium levels. You can avoid this by sticking to the electrolyte recommendations below.
Post-Race: Rehydration is important after the race to replace fluids lost through sweat. You will likely finish the race somewhat dehydrated. Drinking water along with an electrolyte-rich beverage can help restore what has been lost.
Electrolytes, particularly sodium, are lost through sweat and must be replaced to maintain muscle function. Electrolyte concentrations (particularly sodium) from commercial products may not be sufficient for optimal hydration, especially in hot/humid conditions, so always check your food labels carefully. Additional sources of sodium should be considered with the aim of taking on 500–700 mg/l of fluids.
Electrolyte replacement can be achieved through sports drinks, electrolyte tablets, or salty foods like pretzels or crackers. It’s important to practice your hydration and electrolyte strategy during training to determine what works best for you.
Ever notice how, even when you feel full, there’s always room for dessert? This phenomenon where your appetite renews when presented with a new flavour is based in science. Sensory-specific satiety or flavour fatigue is where the pleasure derived from consuming a particular type of food decreases as you eat more of it, leading to a reduced appetite for that specific food. While that raspberry energy gel might taste good the first time by the time you have 10 of them in a row it’s not going to be looking too attractive.
During an ultramarathon, if you are consuming the same flavours and textures repeatedly each bite can become less appealing than the last, causing a drop in fuel intake when you need it most.
Strategies to Combat Taste Fatigue
Variety: Prepare a range of flavours: sweet, salty, savoury, to keep your palate engaged. Include both solid and liquid options to vary textures and temperatures.
Rotate Fuelling Options: Avoid sticking to the same foods at every aid station. Mix it up with gels, bars, and real foods.
Have the things you enjoy: Stock up on some of your favourite treats and reserve for later in the race when regular options start to lose their appeal.
Caffeine is one of the most well-researched and effective ergogenic aids available. It can enhance endurance by increasing alertness, reducing perceived effort, and potentially mobilising fat stores for energy.
There is a wealth of evidence showing the benefits of caffeine on sports performance when taken at a dose of 3-6mg per kilogram of bodyweight4. This level of intake can help sustain mental focusImportantly it will also delay fatigue, which is particularly vital in the later stages of an ultramarathon.
It’s also important to time caffeine intake strategically. Some athletes prefer to reserve caffeine for the latter stages of the race when fatigue sets in, using it as a boost to push through the final miles. Others might take a dose of 3-6mg/kg at the start of the race and then “top up” with smaller doses throughout to maintain a steady level of alertness. Athletes should time their doses based on the approximate half-life of caffeine which is 4-5 hours, so if you take 300mg at the start of the race, at the five-hour mark there will be about 150mg left. Individual tolerance to caffeine varies, so it’s essential to test its effects during training to avoid negative side effects like jitteriness or gastrointestinal discomfort. It is worth experimenting with caffeine dosing/timing in some of your long runs to figure out what works best for you.
The timing of your nutrition intake is just as important as what you consume. Proper timing ensures that your body has a steady supply of energy throughout the race, helps to maintain blood sugar levels, and supports sustained performance.
Pre-Race Nutrition
24-48 Hours Before: Focus on high-carbohydrate, moderate-protein meals with low fat content to maximise glycogen. A common mistake I see in athletes in their carb-loading phases is they see it as a chance to just eat whatever they want. They will consume lots of rich foods with a high fat content which fills them up long before they hit the carbohydrate content they need. So instead of carbonara and croissants try tomato-based pasta sauces, jam sandwiches and sweets.
Morning of the Race: Have a carbohydrate-rich breakfast 3-4 hours before the start that’s lower in fat and fibre. Prioritise carbohydrates and include a small amount of protein. These races often start early so don’t worry too much if you’re eating a little closer to the start time, as long as this is something you are used to doing in training and you are eating foods that you are familiar with you should be fine.
One bonus tip for this meal is based on the fact we know that overnight some of our liver glycogen is used to fuel the brain and other tissues, so including a source of fructose in your breakfast will help replenish this. We have research showing that fructose is particularly efficient at replenishing these stores in the liver5,6. Lucking breakfast staples like fruit, honey and jam will do the trick!
During the Race
Early Stages: Start fuelling early, within the first 30 minutes of the race, to stay ahead of energy depletion. Consume small, frequent amounts of carbohydrates. Even in the early stages, consider incorporating a variety of fuels—gels, chews, and small bites of solid foods.
Mid to Late Stages: Continue to consume carbohydrates regularly. Consider incorporating some protein and fat, to avoid sensory-specific satiety and provide additional energy sources.
Practice Your Nutrition Strategy: The race is not the time to experiment with new foods or drinks. Practice your nutrition plan during long training runs to ensure it works for you. Pay attention to how your body responds to different foods, and fine-tune your strategy based on these experiences.
Do your Research: Check out your race information pack or contact the organisers so you know exactly where each aid station is going to be and what foods/drinks are going to be available so you can factor this into your plan.
Be Flexible: Conditions on race day may require adjustments to your nutrition plan. Be prepared to adapt based on how you feel, the weather, and the availability of food at aid stations. Mental flexibility is as important as physical preparation—being able to adjust your plan on the fly can make the difference between a strong finish and struggling to complete the race.
Listen to Your Body: Pay attention to your hunger, thirst, and energy levels throughout the race. Adjust your intake as needed to stay fuelled and hydrated. If you start to feel nauseous or bloated, it may be a sign to slow down your intake, switch to more easily digestible foods, or adjust your hydration strategy.
Seek Expert Guidance: If you’re new to ultramarathons or looking to optimise your nutrition strategy, consider consulting with a sports nutritionist who can tailor a plan to your specific needs and goals. An expert can help you navigate the complexities of ultramarathon nutrition, ensuring that you’re well-prepared for race day.
Proper nutrition is a critical component of ultramarathon success. By understanding and implementing evidence-based strategies you can optimise your performance and increase your chances of crossing the finish line strong and generally enjoying your experience out in the field.
The best nutrition plan is one that is personalised to your needs, honed through practice, and flexible enough to adapt to the dynamic conditions of an ultramarathon. With the right fuelling strategy, you’ll be well-equipped to tackle the unique challenges of ultra-endurance running and conquer any physical or mental obstacles in your path.
1 Stellingwerff, T. Competition Nutrition Practices of Elite Ultramarathon Runners. Int J Sport Nutr Exerc Metab 26, 93-99, doi:10.1123/ijsnem.2015-0030 (2016).
2 Tiller, N. B. et al. International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing. Journal of the International Society of Sports Nutrition 16, 50, doi:10.1186/s12970-019-0312-9 (2019).
3 Burke, L. M. & Kiens, B. “Fat adaptation” for athletic performance: the nail in the coffin? Journal of Applied Physiology 100, 7-8, doi:10.1152/japplphysiol.01238.2005 (2006).
4 Wang, Z., Qiu, B., Gao, J. & Del Coso, J. Effects of Caffeine Intake on Endurance Running Performance and Time to Exhaustion: A Systematic Review and Meta-Analysis. Nutrients 15, doi:10.3390/nu15010148 (2022).
5 Gray, E. A., Green, T. A., Betts, J. A. & Gonzalez, J. T. Postexercise Glucose-Fructose Coingestion Augments Cycling Capacity During Short-Term and Overnight Recovery From Exhaustive Exercise, Compared With Isocaloric Glucose. Int J Sport Nutr Exerc Metab 30, 54-61, doi:10.1123/ijsnem.2019-0211 (2020).
6 Décombaz, J. et al. Fructose and galactose enhance postexercise human liver glycogen synthesis. Med Sci Sports Exerc 43, 1964-1971, doi:10.1249/MSS.0b013e318218ca5a (2011).
