Updated December 2, 2025 10:11AM
The carb revolution is upon us, y’all!
Runners, triathletes, and cyclists are breaking records almost daily, in large part, they say, due to improved fueling strategies—specifically high-carb fueling.
At the New York City Marathon on November 2, Joe Klecker slammed a staggering 175 grams of carbs per hour en route to a 10th-place finish in his debut. A few weeks before that, triathlete Solveig Løvseth took in 132 grams of carbs per hour during the marathon en route to winning the 2025 Ironman World Championship. And she wasn’t even an outlier.
We’re seeing improved performances, faster recovery, and fewer bonks just, seemingly, by slamming down bars, gels, and drinks all to hit the magic number of 120 grams of carbs (or more) per hour. That’s what many publications, nutrition brands and retailers, and influencers (you know who they are) are also saying.
Call me a cynic, but I’m inherently skeptical of any brand, retailer, or individual pushing an agenda that serves their bottom line.
You may be desensitized to this 120 number now. But lest we forget that it’s a shocking leap from just a decade ago, when the goal was to take in 30 to 60 grams of carbs an hour, max. The goal, scientists believed, was to preserve muscle and liver glycogen. Science has progressed since then, largely thanks to the finding that precisely combining various forms of carbohydrates allows for higher absorption rates. And yet, current scientific recommendations top out at 90 grams of carbs per hour.
So what’s the deal with 120 grams of carbs and more? It’s seemingly working for some pros, what does that mean for most of us? My curiosity led me to a pair of experts who have done their homework: Roxanne Vogel, PhD in exercise physiology and director of R&D at GU Energy Labs, and Paul Booth, a PhD candidate and nutrition coach for Tom Evans and Ruth Croft, who both won the 2025 Ultra-Trail du Mont-Blanc.
Carbohydrate Complexity
With the help of her nutrition coach Paul Booth, Ruth Croft used a dynamic fueling strategy en route to winning the 2025 UTMB. (Photo: Peter Maksimow)
Booth brought us straight back to the science, which he says, is not a fluke.
“There’s a pretty big emphasis right now on 120 grams as a catch-all for anyone,” Booth says, “but the data isn’t there. Follow the science, not what someone is saying online. No one has found any benefits over 100 grams, if not closer to 90. One of the most famous studies shows that the optimal amount is actually 80 grams. Our lab found that 90 was best and dropped off above that.”
Not only is there an upper limit to performance gains, Booth is saying, but performance actually declines once you carb up too high.
The super-high carb dogma leans on simple yet tenuous logic: More is more. Research shows this is true for up to around 90 grams, but above that is where things start to get murky. Making the case for 120 requires cherry-picking studies or relying on anecdotal evidence—in short, pseudoscience. For example, some data on sub 2:30 marathoners suggests substrate oxidation improves above 90 grams, but the study doesn’t correlate it to improved performance outcomes. You have to connect those dots yourself, which comes with its own set of risks.
Research on non-elite runners shows an even cloudier story. Amateurs who are trying to imitate pros are likely over-carbing, with oxidation efficiency—your body’s ability to burn carbs and fat for fuel—going down from 86% at 90 grams to 75% at 120. This difference may sound minor, but in long races like ultras it adds up: 13 unoxidised grams of carbs per hour vs 30 is a lot of carbs just floating around in your gut.
“There isn’t a single peer-reviewed study that shows performance benefits over 90-grams of carbs,” Vogel says. “It costs more, risks more, and has no proven performance benefit.”
In fact, there’s some evidence that going above 90 grams accelerates muscle glycogen depletion and reduces performance.
One Size Does Not Fit All
I’m generally skeptical of one-size-fits-all recommendations and sure enough, the science is much more nuanced, too. One study on personalized carbohydrate fueling emphasizes that the amount individuals should take varies significantly, emphasizing that fueling based on individual oxidation rates outperforms high-dose blanket strategies.
“Emerging research shows significant variability due to factors like body size, exercise intensity, and sex,” Vogel says. “Body size is positively correlated with the ability to oxidize ingested carbs, suggesting that traditional guidelines are over-feeding some while under-fueling others. Intake should be individualized based on body size, with a target of approximately 0.7 grams of carbs per kilogram of body weight per hour.”
Evidence from two of the best ultra runners in the world—Tom Evans and Ruth Croft—supports this as well.
“Tom [Evans]’s average intake during UTMB was 94 grams and Ruth [Croft] was roughly at 90 grams,” Booth says. “In lab tests with Tom we found that he could oxidize 1.7 grams per minute at his max, which is quite high. For his pace at UTMB, we didn’t need to be at that level all the time because it would be over-fueling. Instead, we varied it based on the demands of the course, feeding him more before sections that he would dig deeper, then back down to give his gut an easy section.”
Not only is the gold standard different from athlete to athlete, then, but also within each athlete depending on the context. Fueling dynamically with your output and the demands of the course may often be the best course of action.
What the scientists say: Start with 80 to 90 grams of carbs an hour and go from there. (Photo: Luke Webster)
Tummy Troubles
Personalized trials also show a lower rate of perceived effort and less stomach fullness with under 90 grams, which is associated with GI discomfort. This makes sense, as a personalized dose means there are fewer unoxidised carbs accumulating in your gut. In other words, aiming for a blanket 120 carbs per hour increases the odds you’ll have GI issues (and DNF), instead of improving your finishing times.
“There may be some utility for world-class athletes in multi-day events where recovery is challenging and the opportunity to fuel is limited, but gut training is required,” Vogel says. In all other cases, “there is no point in ingesting carbohydrates in sports drinks and gels that aren’t metabolized, especially for non-elite athletes. It just increases the risk of gastrointestinal issues.”
Breaking It All Down
A 2020 paper focused on recovery kickstarted the carb revolution in trail running. The lead author, Aitor Viribay, was working for Ineos Grenadiers at the time and pulled the concept from cycling. Since then, the Western States 100 has seen 14 of its 15 fastest female times and 12 of the 15 fastest male times, which is not a coincidence. The increase in carbs (along with training and technological improvements) has made a huge impact, but there are limits to everything.
My broad takeaway from talking with Vogel and Booth and reading the research is this: There is no need for most athletes to strive for such astronomically high carb intakes, and in some cases it may actually be to their disadvantage. As a general rule of thumb, imitating everything a pro athlete does isn’t ideal for most amateurs and in this case, over-fueling comes with its own risks, namely GI issues.
The big problem with 120 grams per hour is that it is becoming the default baseline, not a rare outlier for just a few world-class athletes. Most runners should start with 80 or 90 grams per hour (which, again, is three times the recommendation from only a decade ago!) and then, if possible, get individualized testing to adjust as needed.
That’ll do a lot more good than listening to the influencers and brands who are trying to sell you more stuff.