Evidence-Based Fueling Strategies in Ultrarunning Today
- Brittany Peterson
- 8 hours ago
- 9 min read
Ultrarunning is a sport that has taken off in the last few decades and today is getting constant attention in terms of best training practices, top fueling strategies and additional means of progressing athletes toward their highest abilities and performances. We have seen the sport go through various phases of recommendations in terms of nutrition and fueling strategies geared towards performance. The purpose of this article is to review the top recommendations on how to make sure you are fueling in the most optimal way to maximize your gains and performance abilities - based on what we know today.
Before we dive into the current research regarding race day recommendations, it is important to highlight the importance of ensuring your day-to-day nutrition is also considered, as being well nourished is an essential foundation for performance. Many athletes find themselves in unintentional caloric deficit due to the nature of training volume and the time spent in training, which if not observed and corrected can lead to significant health concerns, such as Relative Energy Deficiency in Sport (RED-S), which can impact performance, general health, energy availability, bone health and hormone function (Cabre, et al., 2022). Therefore, considering all aspects of nutrition is truly essential in order to maximize your abilities on race day.
How exactly does an athlete optimize fueling strategies during ultramarathons? There are several key areas to consider. This article will review the following evidence-based fueling strategies:
Individualization
Carbohydrate Recommendations
Hydration and Electrolyte Strategies
Protein Recommendations
Real Food versus Engineered Products
Caffeine Considerations
Individualization
We can share the latest research and resulting recommendations, but it is important to first state how there is no single fueling approach that will work for all athletes. There are many factors that we need to consider - body size, metabolic efficiency, gut tolerance and external factors such as terrain and temperatures. These factors will result in each athlete potentially having a very different experience with the timing, quantity and type of fueling recommendations. Therefore, it is very important that an athlete practices their race day fueling strategies in training.
There is evidence supporting the fact that diet can have an impact on the body’s ability to absorb nutrients. For example, a high-carbohydrate diet can make adaptations in the body that allows greater carbohydrate absorption and oxidation during exercise (Jeukendrup, et al., 2017). Jekendrup, et al. (2017) therefore concludes, “Fueling success in ultras is less about the perfect product, and more about a well-trained gut and adaptable plan.”
Therefore, the first recommendation of this article is to practice your fueling strategy. This is essential on long runs (greater than 90 minutes), but it is important to also highlight that an athlete needs to “train their gut” during higher intensity speed workouts as well. Adding this as a critical aspect to your training can help you feel confident that your nutrition strategy and selected products or food items will be tolerated by your GI system. It also gives you the opportunity to assess the effectiveness of your individualized nutrition plan. You’ll have the ability to see energy fluctuations, effectiveness of fueling sources and how your recovery is impacted following your training sessions. This practice also gives you the opportunity to learn what you prefer, establish your “go-to’s,” determine if you have any flavor preferences and start practicing the timing and frequency of your fueling strategy.
Carbohydrate Recommendations
Carbohydrates (CHO) are at the center of fueling recommendations to maximize performance and there are several reasons to support why. First, there is limited storage available in the body for carbohydrates, which means that the CHO levels can be quickly adjusted in terms of adding to the supply as well as depleting from it. One can eat carbohydrate rich foods and quickly increase the supply, while at the same time deplete the supply through exercise. Next, carbohydrates are a primary energy source for the brain and the muscles and it supports the body during a range of exercise demands, from anaerobic pathways (high intensities) as well as oxidative pathways (longer, steady efforts). Finally, carbohydrates are more efficient than fats for producing energy during exercise, particularly at high intensities, where they allow the body to generate more energy with less oxygen (Thomas, et al., 2016).
To summarize, carbohydrates are vital for both immediate energy gains and consistent fuel during varied physical demands, which makes it an essential fueling tool to maximize an athlete’s performance during an ultramarathon.
What are the current thoughts on how much CHO intake an athlete should be consuming during ultraendurance events? This is a nuanced answer with several considerations. A conservative recommendation is approximately 60 grams of CHO per hour (Tiller, et al., 2019). This recommendation is still recognized in shorter distance races, generally 2-3 hours in total. However, more studies are agreeing that 90 grams of CHO per hour is the recommended intake, particularly for longer distances (greater than 2.5 hours) because it can further improve athletic performance and delay exercise-induced muscle damage (Thomas, et al., 2016; Jeukendrup, 2014). With this, there are other studies exploring the potential benefits of pushing beyond the 90 grams of CHO per hour and exploring results with 120 grams of CHO per hour (Viribay, et al., 2020). There are various findings in the research, but there are results indicating a possible fueling advantage. The limiting factor is how much CHO can your body actually utilize and absorb. Research is now confirming that the higher CHO grams per hour can be utilized if you train your body to absorb higher quantities and this happens by training your gut by ingesting more carbohydrates and working up to these higher quantities (Burke, et al., 2019). If an athlete hasn’t properly trained their body to take on these higher quantities of CHO per hour the risk is excess CHO not getting absorbed which will likely lead to GI distress.
The takeaways here are that 90 grams of CHO per hour is the general standard to work toward for carbohydrate intake during an ultrarunning event. However, an athlete needs to practice their fueling strategy, progress toward tolerance of the 90 grams of CHO per hour and evaluate if their bodies are adapting properly in order to absorb the carbohydrates to allow the benefit as well as reduce the risk of excess carbohydrates leading to GI distress.
Hydration and Electrolyte Recommendations
Like many aspects of nutrition, hydration is another area that is highly specific to the individual. Diminished exercise capacity can be linked to insufficient fluid replacement and subsequent dehydration, so it is important to problem solve the right equation for the individual athlete. There are varying theories of hydration replacement recommendations, one of them being “drink to thirst.” This is drinking when you are thirsty, which can be sufficient in shorter durations (less than 90 minutes), in ideal conditions (i.e. cooler temperatures) and during lower intensities (Kenefick, 2018). However, when it comes to an ultramarathon having a more specific plan is critical. The key is to drink enough to ensure you don’t lose more than 2% of body weight (Thomas, et al., 2016). An athlete can determine their individual sweat rate, which can be integral to personalizing their hydration plan. It is important for an athlete to consider the variabilities of their sweat rate depending on the intensity, duration, their current fitness, their heat acclimatization, current altitude, and other environmental conditions (Thomas, et al., 2016). An athlete can estimate their sweat rate by measuring their nude body weight before and after exercise (Kenefick, 2018). This sweat rate then allows an athlete to individualize their fluid supplementation strategy to their own specific sweat rate.
A general recommendation is that ultrarunners should aim to consume 150-250 mL of fluid approximately every 20 minutes during exercise, or 450-750 mL of fluid per hour (Tiller, et al., 2019). However, it is also noted that this will need to be adjusted to the particular demands of the event as well as specificities of the athlete (i.e. race duration, environmental demands, fluid tolerance, body mass, prior gut training, etc.). For example, if an athlete knows they have a higher sweat rate they will need to consider higher amounts of fluid replacement per hour.
When it comes to hydration we must also remember that when you sweat, you lose sodium and other minerals and therefore having an electrolyte mix as part of your hydration plan can be essential. The recommended amount of sodium replacement is highly variable, 200 mg per hour up to 1500 mg per hour depending on the individual (Thomas, et al., 2016). This is where formal sweat testing gives added data on individual electrolyte losses as well as quantifying your sweat sodium concentration. This allows an athlete to be much more precise with electrolyte replacement and determine if there is a drink mix that meets their requirements or if they will supplement specific electrolytes via capsules.
Dehydration can have a significant impact on energy levels because it can cause reduced blood volume which leads to reduced blood flow to your gut which negatively impacts the ability of your body to absorb nutrients. It can also lead to GI distress which further impacts absorption rates.
Additional Considerations
Finally, there are a few other considerations to add to optimizing performance during ultrarunning races. First, carbohydrates are the prime nutritional component athletes are focusing on, however we shouldn’t leave out protein. Adding 5–10 g of protein per hour may support muscle preservation and reduce perceived exertion in ultras longer than 6 hours (Tiller, et al., 2019). Second, an athlete should consider mixing in real foods during ultrarunning, particularly events where you are essentially missing several meals throughout the day. Adding in real food sources can assist with taste fatigue, hunger or feelings of “emptiness” in the stomach as well as provide greater longevity to your energy supply. Adding real food to the nutrition plan for a longer ultrarunning event can also maintain a balanced gut and assist in avoiding GI distress (if practiced to ensure your selected food items complement this process). Finally, caffeine should be used strategically during an ultramarathon event. It is recommended to utilize caffeine in later stages of ultrarunning events in order to combat fatigue, enhance alertness and sustain exercise performance. Generally 3-6 mg per kg body weight has been shown to improve “muscular endurance, movement velocity and muscular strength, sprinting, jumping, and throwing performance, as well as a wide range of aerobic and anaerobic sport-specific actions” (Guest, et al., 2021). Potential benefits could be observed with as low as 2 mg per kg body weight. It is important to note that you can have an increased risk of GI distress or other negative side effects when you have too high of a dose (greater than 6 mg per kg body weight) or with excessive use. You also want to be mindful of timing of caffeine intake to avoid unnecessary spikes and drops in energy level. For example, if you are running a 100km race, plan your caffeine intake to begin past the half way point in the race and then strategically implement regular caffeine supplementation in the later phases of the race (versus starting with it early and having random gaps without use or risking GI distress with overuse.
To review, there is significant research today to help guide an ultrarunner in finding the best nutrition strategy to maximize performance during an ultramarathon event. The research is ongoing and new developments are being made regularly so it is important to continue to follow the research for latest recommendations, while emphasizing that the most important consideration is to make sure that these recommendations work for the individual athlete. The general takeaway of this article is that the individual athlete needs to practice their fueling strategy to determine what will work best for them, and the fueling strategy includes the broader view of nutrition (carbohydrates, proteins, real foods, engineered products, etc.) and sufficient hydration that considers electrolyte supplementation as well.
Bibliography
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Cabre, H. E., Moore, S. R., Smith-Ryan, A. E., & Hackney, A. C. (2022). Relative Energy Deficiency in Sport (RED-S): Scientific, Clinical, and Practical Implications for the Female Athlete. Deutsche Zeitschrift fur Sportmedizin, 73(7), 225–234. https://doi.org/10.5960/dzsm.2022.546
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About the Author:
Brittany Peterson is a Running Coach at Peak Run Performance and a professional trail and ultra runner. She has had several wins in key races throughout the world and has been a 3-time finisher at the Western States Endurance Run, with 2 of her 3 results being in the top 5. She comes from a background of track and field and road marathon running as well and loves coaching athletes of all ages, abilities, in all terrains and with any goal in mind.
For more information and resources, check out our website at: https://www.peakrunperformance.com/
Date Published: October 2025
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