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Time to role play. You’re about to race a mountain marathon with 9000 feet of technical climbing and descending that will take more than 5 hours. If you win, you accomplish a lifelong dream and automatically qualify for Team USA at the World Trail Running Championships. Anything else, and you go home with sore legs and questions about what might have been.
The stakes are high. Every second counts. You are betting on a breakthrough. How do you fuel?
Michelle Merlis faced this scenario heading into the 2022 Breakneck Trail Marathon, a monster of a race that appeals to athletes who are masochistic or naive. Qualifying for Team USA was her moonshot when she picked up trail running years ago. She had always been tough and fast, but there are thousands of tough and fast athletes that won’t make Team USA in their careers. One shot, one opportunity. Would she capture it, or let it slip?
And when Michelle’s knees were weak and her arms were heavy, she counted on her figurative mom’s spaghetti–a high-carb, high-calorie fueling plan. When she needed a breakthrough, she consumed 510 to 540 calories per hour!
Her 2017 time in finishing 4th at this race: 6:40:56.
Her 2022 time to win and qualify for Team USA: 5:26:53.
In those 5 years, she worked her butt off in training, demonstrating character and resilience through ups and downs that made the Breakneck course look like the Chicago Marathon. But a key logistical part of her journey was refining her fueling so that her fitness could shine when it counted, after hours of pushing the limits. With the help of nutritionist-to-the-stars Kylee Van Horn (who works with tons of pro athletes), Michelle found that she could push her fitness limits by pushing her fueling limits.
Last week’s article was on standard, sustainable fueling practices. This week’s article turns it up to 11. EXTREME!
The previous article reviewed some of the studies on fueling practices before and during races for peak performance. I concluded with a suggestion of 250-350 calories per hour, focused mostly on carbohydrates. But there were some hints of more extreme approaches that could work. In today’s follow-up article, I want to stop being coy, and tell you what my co-coach Megan and I have seen in practice.
Many of the best athletes in the world fuel way, way more than you might think.
But it varies wildly! Nutrition is a fascinating field because biochemistry, genetics, and environment interact over time to create hugely different experiences. On one side, you can have Michelle and some of the other pro athletes we see who push 400+ calories per hour without any issues. On the other side might be athletes like John Kelly, who has had stomach issues that often prevent him from taking in high calorie totals during his record-breaking multi-day FKTs, sometimes amounting to 100-200 calories per hour. And in a whole other bucket are “fat-adapted” athletes who describe limiting calorie intake altogether. There is no one-size-fits-all answer because our GI tracts, microbiome, and physiology/training are fundamentally different.
That’s why I love the examples of what athletes actually do in practice. Take it out of the lab and you’re on a one-way trail into my heart. I have a request to any scientist out there reading this article: please conduct a study on the mid-race fueling of the best athletes in the world, like this one from the journal Sports Medicine–Open on training methods that I reviewed in an April article.
Biochemistry and exercise physiology give us some clues of what should work. But what happens when theory is put into the 20,000-degree pressure cooker of race settings where every second counts, whether a second is lost to depletion or GI distress?
How Much Should You Eat During Trail Races? Extreme Fueling Practices
Ultra superstar and scientist Patrick Reagan has described consuming over 400 calories per hour. In a 2017 Runner’s World article, Jim Walmsley said he aimed for 400-450 calories per hour. If you Google “[athlete name] calories per hour,” there are a bunch more examples of athletes consuming over 400 calories per hour during races. Many pro cyclists consume 400-500 calories per hour during races, where GI distress is less likely and there may be more isolation of what works best for physiology (though given the history of cycling, I wouldn’t trust anything published willingly by a pro team). Gosh, I wish we could have a comprehensive study on this topic!
In coaching, I have seen Clare Gallagher around 450 calories per hour. World-class athlete and nutrition expert Alex Borsuk Hasenohr aims for 400+ calories per hour, with many other pro athletes aiming for similar totals. And Michelle really pushes the limits, prompting me to write this article today. In the final few hours of Breakneck, she consumed 540 calories per hour, consisting of a 180-calorie Awesome Sauce gel every 20 minutes.
That compilation of N=1 anecdotes is contrasted by athletes that stick to a more common ~250-300 calories per hour, or even less. My big question: could the higher intakes I am seeing in top professional athletes be indicative of an underlying physiological benefit for some athletes to chase breakthroughs?
Or is it just statistical noise, availability bias, or some other peril of anecdata? The jury is out.
Here’s What The Science Says About Ultra Fueling: Study Overview
But an amazing 2020 study in Nutrients by a research team led by Aitor Viribay Morales provides some clues that may be instructive in trying more extreme fueling approaches. The study went into the field to ask the question: How many calories can athletes actually stomach? And what are the implications of raising that number as high as possible?
The study started with 31 elite male runners volunteering as tribute, including 2 world champions, prior to competing in a mountain marathon with 6600 feet of climbing. The inclusion criteria required gut training, meaning consuming up to 90 grams of carbs per hour in at least 2 runs per week in the previous 4 weeks. They also required at least 5 years of ultra experience, and no performance or medical supplements in the 7 days before the race. That knocked off 5 of the 31 participants, leaving 26 athletes that were split into three groups:
- The experimental group consuming 120 grams of carbohydrates per hour, taken as a 30 gram gel every 15 minutes. This equates to 480 calories per hour from carbs alone.
- The control group consuming 90 grams of carbohydrates per hour, taken as a 30 gram gel every 20 minutes. That aligns with research-backed recommendations, like those I made in last week’s article.
- The “low” group consuming 60 grams of carbohydrates per hour, taken as a 30 gram gel every 30 minutes. The “low” group overlaps with what studies have shown some ultrarunners actually do in practice, though many studies show intakes as low as 30-50 grams per hour.
During the race, athletes who had injuries or GI problems were told to drop out, leading to another six being axed from the results (3 for injury, 3 for “reflux and/or flatulence”–also known as the “Roche combo”). So we had 20 athletes total left to battle in the No Hunger Games. They consumed the calories via 2:1 glucose:fructose gels, designed to prevent overloading of gut transporters for carbohydrate sources (see this 2015 review in the Journal of Strength and Conditioning Research). Blood tests were taken before and after the race to measure for biomarkers of muscle damage.
Now is the time we take a step back. What do you think happened? I would guess that the control group is the best situated. Four gels an hour just seems like SO MUCH, right?
The results were striking. The experimental group significantly reduced markers of exercise-induced muscle damage, including creatine kinase and lactate dehydrogenase, which have been associated with fatigue in longer races. That’s incredibly cool! A 2012 review article in The Journal of Physical Fitness and Sports Medicine outlines some of the possible mechanisms related to intracellular calcium accumulation, particularly when read together with a 2011 study in the Journal of Physiology on how glycogen availability affects these concentrations. But the numerous pathways involved are immensely complex in practice, and not fully understood.
Perhaps most interestingly, the experimental group had significantly lower total exercise load, calculated based on perceived exertion at the time of completion multiplied by marathon time. For how fast the athletes went, they reported that the marathon was less difficult when they got to the finish line than those taking in fewer calories.
What an amazing study design!
Talk about pushing the limits of what we think is possible! The wider applicability of the results hinges on a few questions.
First, can the findings be extrapolated to a broader cohort of athletes?
These were elite male athletes, and it’s possible that it may apply less to female athletes, or to athletes competing at lower intensity levels. (It may be a quirk of a small sample size, but most of the athletes I coach who consume 400-500+ calories per hour are women. Since fat oxidation rates vary more for the average man than the average woman, perhaps some men run into a possible downside with consistently using extremely carb-heavy fueling approaches in training: reducing fat oxidation efficiency, whereas women don’t face that risk. That’s pure speculation, though.)
On the flip side, the science of glycogen metabolism and performance should be generally applicable. Glycogen is not just important for energy storage, but for cell signaling, metabolism, and muscle function as well. A super cool 2015 review in the Scandinavian Journal of Medicine and Science in Sports looked at how glycogen availability impacts cell function, and it’s a great intro to how it goes beyond a simple formula of calories in and calories out.
Second, how might GI distress play a role in very high-energy intakes?
In this study, 2 of the 3 participants that dropped out due to “reflux and/or flatulence” were in the experimental group, with the other drop-out coming from the control group, in an event that took under 5 hours to complete on average. It’s possible that in a wider study, it will be consistent that 20%+ of athletes will have GI distress at such high fueling levels. Maybe the percentage gets higher still in longer events, when the gut has to process more calories over time. Or maybe there are lower percentages in longer events since the intensity goes down with the added distance. It’s also possible that the athletes who can expect GI distress will remain steady over time, and they can reduce intake while the other athletes keep it extreme. Or perhaps the entire experimental group would be at risk, with variance depending on the day.
For context, a 2022 study in Frontiers of Physiology found higher rates of gut distress in athletes taking in 90 grams per hour relative to those taking in 76 grams per hour, and I imagine that many athletes would run into an additional problem of fueling fatigue/gagging if they overfuel.
Finally, how do the extremely high intakes in this study interact with real-world fueling patterns?
These athletes were getting all of their calories from gels, and it’s possible that the results would look different with liquid fueling sources, or fuel that also contained fat and protein. What if an athlete counts on potato chips from aid stations (in the new Lay’s flavor, “Germ-Infested™”)?
Conclusions from Fueling Articles
My big takeaway on the fueling articles I have written is a bit unsatisfactory: you have to get comfortable with individual variability. Experimenting with these extreme intakes could lead to amazing benefits, or it could lead to amazing flatulence, or it could lead to a mix of both depending on the day, the intensity, and the conditions.
Ideally experiment with these higher totals when working with a nutrition expert, trying to find calorie sources that work best for you. That’s why Megan and I partnered with Spring Energy a couple years ago to create Awesome Sauce, a 180-calorie fueling option that was the staple of Michelle’s strategy. We saw the science and thought we saw an opportunity, but also realized that trying to stomach a traditional gel every 15 minutes is daunting.
Try Awesome Sauce, try gels, try sports drink, try real food…. But make sure you try it first. Pushing the limits of physiology and performance always comes with some risks. Taking those risks might lead to a lifelong breakthrough, like badass boss Michelle Merlis.
Or it might lead to breakthrough flatulence. Either way, hold onto your butts.
David Roche partners with runners of all abilities through his coaching service, Some Work, All Play. With Megan Roche, M.D., he hosts the Some Work, All Play podcast on running (and other things), and they wrote a book called The Happy Runner.