Ultramarathons have sometimes been called an eating contest while running, given the need for consistent fueling throughout the events. Ultrarunners competing in a 24-hour trail ultramarathon (covering from 75-130 miles) have been documented to expend up to 18,000 calories over those 24 hours (Costa et al. 2014). Avoiding a caloric deficit is impractical, but avoiding an excessive energy deficit is necessary for optimal performance. So how can you optimize your fueling and hydration strategy during ultramarathon events?
Based on a synthesis of research-based recommendations, ultrarunners should aim to consume the following while racing (Sawka et al. 2007; Thomas et al. 2016; Tiller et al. 2019):
- Calories: 150-400 total calories per hour
- Carbohydrates: 30-90 grams (120-360 carbohydrate calories) per hour
- Protein: 5-10 grams (20-40 protein calories) per hour
- Fluid: 400-800 mL of fluid per hour (~150-250 mL every 20 minutes)
- Sodium: 500-700 mg of sodium per liter of fluid
Within these ranges, you should find where your individual tolerance lies with an eye on food palatability, the greater preference for savory foods that comes in the later stages of an ultramarathon, and the recognition that “fluid and electrolyte requirements will be elevated when running in hot and/or humid conditions” (Tiller et al. 2019).
In the rest of this article, I discuss these research-based recommendations in more detail and provide practical guidance to help you develop and implement your own ultrarunning fueling and hydration plan.
During aerobic exercise, the body uses both carbohydrates and fat as energy sources. A supply of both macronutrients are required since fat burns in carbohydrate’s flame. Although a body’s fat stores are relatively plentiful, the body needs a consistent supply of carbohydrates for activities beyond a few hours. This is because the body’s storage of carbohydrate — in the form of muscle and liver glycogen — is limited.
As Rapoport (2010) summarizes, “An apparent paradox of long-distance running is that even the leanest athletes store enough fat to power back-to-back marathons, yet small carbohydrate reservoirs can nevertheless catastrophically limit performance in endurance exercise.” This is why a whole industry has risen up around sports drinks and gels that can easily be ingested during races.
Although it is practically impossible to take in enough calories to match the caloric expenditure during a long event, “A closer match between energy expenditure and intake, especially carbohydrate provisions, is associated with better performance outcomes and less physiological disturbances” (Costa et al. 2014: 132). However, simply eating more risks gastrointestinal problems due to the difficulty of digesting food while exercising. So how much should you aim to ingest while balancing these competing concerns?
Guidelines for Carbohydrate Intake
For endurance events that last from 1-2.5 hours, 30-60 grams of carbohydrate per hour are recommended; but for ultra-endurance events lasting longer than 2.5-3 hours, up to 90 grams of carbohydrate per hour is recommended (Thomas et al. 2016). This means ultrarunners should be aiming for 240 calories (= 60 grams) to 360 calories (= 90 grams) of carbohydrates per hour.
In practice, intakes of 20-40 grams/hour are more commonly reported (Costa et al. 2019); and taking in more than 90 grams/hour is not associated with any additional benefits (Podlogar & Wallis 2022: S9). During training, start with around 240 carbohydrate calories per hour and gradually increase that amount to the upper limit of 360 carbohydrate calories per hour to find your personal sweet spot.
Studies generally recommend using a 2-to-1 ratio of glucose-to-fructose when ingesting up to 90 grams of carbohydrate per hour (Jeukendrup 2011), although other research has shown that a ratio closer to 1-to-0.8 may be better for gut comfort (Rowlands et al. 2015). The point is that a mixture of these two different simple sugars — also known as a multiple-transportable carbohydrate blend — leads to better absorption than ingesting just one type on its own (Podlogar & Wallis 2022: S9).
But don’t obsess over the details. The key objective is to aim for 240-360 carbohydrate calories (i.e., 60-90 grams) per hour. Experiment with different products and foods to find what works for you in terms of taste and digestibility. There are many great sports drink mixes (e.g., Tailwind) and gels (e.g., SiS gels) designed to provide easily digestible carbohydrates to aid sustained endurance performance. If you have the ability to use your preferred ones during your race, do so. Otherwise, find out what’s available at the race aid stations and use those. Either way, train with what you’ll be using during the race.
To ensure you start your race with adequate glycogen stores, pay attention to your meals in the days leading up to the event and your breakfast on the morning of the event. The increased rest and recovery associated with a race taper, along with proper meals, will allow your body to replenish depleted glycogen stores even without carbo loading. It generally takes 24-36 hours to replenish muscle glycogen stores (Burke et al. 2017) and 11-25 hours to replenish liver glycogen (Gonzalez et al. 2019; see Podlogar & Wallis 2022: S11). Breaking your overnight fast before a morning race can further top off glycogen levels prior to the event, ensuring depletion from the overnight fast is mitigated. In the 1-4 hours prior to the start of the event, aim for 1-4 grams of carbohydrate per kilogram of body weight (Thomas et al. 2016: 557, citing Burke et al. 2004, Ormsbee et al. 2014). Choose carbohydrates with a low glycemic index or along with some protein and fat to dampen the effects of the insulin response. The bottom line is to find what works for you.
Protein During Ultramarathons
Ultramarathons involve skipping normal meals throughout the day. In a long enough race, you will eventually need to take in some protein — especially in the form of real foods that also include fat, rather than just relying on sports drinks, gels, and energy bars all day.
Although research has not shown any performance benefits to taking in supplemental protein during endurance events less than 2 hours in duration (Costa 2019: 133), taking in carbohydrate along with protein (vs. carbohydrate alone) during 6 hours of endurance exercise has been demonstrated to improve net protein balance both during exercise and post-exercise recovery (Koopman et al. 2004).
Guidelines for post-exercise protein intake recommend 0.3 grams of protein per kilogram of body weight every 3-5 hours during meals (Thomas et al. 2016: 552). Since ultrarunners are effectively missing those meals, aiming for a comparable amount of protein every 3-5 hours during an ultramarathon may be warranted.
This means a 130-pound (59-kilogram) runner would aim for 18 grams of protein, a 160-pound (73-kilogram) runner would aim for 22 grams of protein, and a 190-pound (86-kilogram) runner would aim for 26 grams of protein every 3-5 hours.
Put more simply, according to the International Society of Sports Nutrition’s recommendations for ultramarathon racing, aim for 5-10 grams of protein per hour, which is 20-40 protein calories (Tiller et al. 2019).
This could easily be integrated into your fueling strategy with various engineered sports nutrition products. For example, a Clif Bar has 10 grams of protein and a serving of the Tailwind Recovery Mix has 11 grams of protein. Consuming one of these options every few hours would satisfy the protein intake recommendations.
Real foods are another good option, such as a peanut butter and jelly sandwich — or, my preferred version, an almond butter and jam sandwich. A 2-tablespoon serving of almond butter supplies 6 grams of protein, plus carbohydrates and fat — a good real food energy source during a long ultramarathon. Look for opportunities presented by the course terrain to take in real food options like this, such as a long uphill section that you’re power hiking, so that you can eat and start digesting the food before shifting to the jostling of a downhill running section. Again, experiment during training to find what works for you and rule out what you cannot tolerate.
Fluid and Sodium Replacement
How much and what to drink can be highly variable depending on your individual sweat rate and the weather conditions. “Sweat rates vary during exercise from 0.3-2.4 L/h [liters per hour] dependent on exercise intensity, duration, fitness, heat acclimatization, altitude, and other environmental conditions (heat, humidity, etc.)” (Thomas et al. 2016: 556).
A position statement by the American College of Sports Medicine recommends a fluid intake of 0.4 to 0.8 liters per hour “for most athletes and athletic events” (Thomas et al. 2016: 556, citing Sawka et al. 2007). If you’re carrying two half-liter bottles in your running pack, that means drinking one bottle or up to two bottles each hour.
Should you be carrying water or a sports drink in those bottles? Regardless of how you get your fluids, keep in mind that water is required for digestion. So you always need to consider what you’re drinking in conjunction with what you’re eating.
Taking your fluid as a sports drink — rather than plain water — has several advantages. It allows you to take in calories and electrolytes along with water. The combination of carbohydrates and sodium in a sports drink enhances the absorption of these nutrients into the bloodstream. It also allows you to titrate a nice balance of these nutrients at regular intervals, say, every 10-20 minutes.
Let’s take the example of Tailwind’s Endurance Fuel. If you mix two scoops with 590-710 mL as suggested on the label, that gives you 25 grams, or 200 calories of carbohydrates, plus 610 mg of sodium, 90 mg potassium, and 12 mg magnesium. In moderate weather conditions, you might drink just under a half liter over the course of an hour, which could be supplemented by some gels, an energy bar, or solid food to round out your caloric needs. In hotter weather conditions, you may drink closer to a liter over the course of an hour, providing additional sodium and fluid to deal with sweat loss while ensuring you’re getting easily digestible carbohydrates.
Drinking more water than what you lose in sweat and urine can result in the condition of hyponatremia where blood sodium levels drop below 135 mmol/L. This is often exacerbated when relying on plain water or low-sodium fluids, especially when drinking more than 1.5 liters in an hour. This is not to say there are never situations where an ultrarunner may need to consume that much fluid in an hour — for example, an individual with “salty sweat” or a high sweat rate in hot conditions — but that you should be aware of the pitfalls of both underhydration and overhydration. In most situations, “drinking to thirst” (Goulet 2012) can act as a general guide.
Replacing sodium through a sports drink is a good strategy for most ultrarunners, while only those with “salty sweat” may “require some use of sodium-containing foods, capsules, tablets, or highly concentrated electrolyte solutions” (McCubbin 2023: 997). The American College of Sports Medicine (Sawka et al. 2007) and International Society of Sports Nutrition (Tiller et al. 2019) recommend that runners consume sodium in concentrations of 500–700 mg/L of fluid.
Develop and Implement Your Race Nutrition and Hydration Plan
Now that you have a good idea of what to aim for with your fueling, it’s time to develop your own personalized race nutrition and hydration plan.
How long will you be able to stomach the same sports drink and gels during an ultramarathon? Could they satisfy you for 5 hours? Up to 10 hours? What if you’re doing a race that will take 24 hours? At some point, you will need to diversify your food intake. When that will be depends on your personal circumstances. But you need to be ready with some different options that you’ve experimented with during training.
The food you choose needs to meet some basic criteria. It needs to be easy to open while moving. You don’t want it to be too dry because it would be hard to chew. You don’t want it to get stuck in your teeth and annoy you. You don’t want it to be too messy so that it falls apart in your hands before it gets to your mouth. You want it to be easy to swallow and digest. It also should taste good to you.
During your long runs, experiment with different food and drink options to identify both engineered options (e.g., energy bars, gels, sports drinks) and real foods (e.g., pretzels, soup, PB&J sandwich) that include sweet, salty, and savory possibilities.
Identify your options in order of preference, starting with your favorite go-to ones that you will use as long as they continue to work for you, followed by back-up items that are similar, and finally any items you might find at aid stations that you know you could safely stomach. Anything not on your lists should generally be avoided.
Below is an example. The list for each category moves from my favorite items at the top to backup items I might include in a drop bag to items I’m likely to find at aid stations that I could stomach if needed.
- Tailwind Endurance Mix (berry, naked, lemon, orange)
- Tailwind Recovery Mix (chocolate, vanilla)
- Gatorade (orange)
- Reed’s Ginger Brew (de-fizzed if possible)
- Synergy Gingerade Kombucha (de-fizzed if possible)
- Coke (de-fizzed if possible)
- Root beer (de-fizzed if possible)
- Other sports drink brands (berry, orange)
- SiS gels (lemon and orange)
- Gu gels (chocolate)
- Other brands (berry, vanilla, chocolate)
- Energy chews
- Clif Bar (chocolate)
- Kind Bar (sea salt and chocolate)
- Lara Bar (peanut butter chocolate chip)
- Pro Bar (chocolate chip)
- Wild Monkey Bar
Real foods that are sweet:
- Chocolate chip cookies
- Chocolate brownies
- Oreo cookies
- Peanut butter and jelly sandwich
- Waffles with butter and syrup
Real foods that are salty and/or savory:
- Mashed sweet potato with olive oil, balsamic vinegar, and salt
- Dill pickles (and pickle juice)
- Salted dry roasted cashews
- Salted dry roasted almonds
- Sea salt and vinegar potato chips (or similar)
- Salted pretzels
- Hot chicken broth
- Split pea soup (or similar)
You can expand your lists as you continue to experiment and find backup options. But at the very least, include a few backups for the preferred items you will be using until you can no longer stomach them. Be sure to include real foods (and not just engineered foods) that encompass sweet, salty, and savory items.
As you develop your nutrition and hydration plan, keep these points in mind:
- Practice your plan during training runs that mimic race conditions. The closer you get to your target event, the more you should be using the foods you will be racing with during your long training runs. Practice ingesting at regular intervals. If you will be racing in the heat, be sure to practice in the heat. “Training your gut” is just as important as training your legs, lungs, and heart.
- Be ready to switch to your backup food and drink options. Flexibility in what you consume will inevitably be required as you navigate “appetite dysfunction, taste fatigue, and gastrointestinal symptoms [that] are common during ultramarathon events (Costa et al., 2016; Hoffman & Fogard, 2011), so at the end of the day “runners should be flexible to the nutritional items consumed by conceding to cravings or what appears most tolerable” (Costa et al. 2019: 134).
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