- Recent research found that marathoners eating 120 grams of carbs per hour had lower training stress and less muscle damage during the event.
- Current exercise guidelines suggest a range of 30 to 60 grams per hour for endurance athletes, with a ceiling of 90 grams per hour.
- Regularly eating higher amounts of mixed carbohydrates like glucose and fructose during runs can train your gut to tolerate and absorb higher amounts of carbs during exercise.
New research shows that endurance runners who consumed 120 grams (that’s 480 calories, or about five gel’s worth) of carbs an hour during a mountain marathon enjoyed lower physiological stress and significantly less muscle damage than their peers who ate fewer carbs during the event.
That’s two to four times the generally recommended 30 to 60 grams (120 to 240 calories) an hour, and 30 grams (or one large banana) more than the previously recommended upper limit of 90 grams of carbs per hour. But it is not outside of the range of what the best athletes in the world, such as world record marathoner Eliud Kipchoge and four-time Tour de France winner Chris Froome routinely take in during competitions, says lead researcher and sports performance nutritionist Aitor Viribay founder of glut4science.com.
“Although 90 grams per hour has been proposed in the literature, there are physiological reasons that 120 grams per hour could be a more suitable limit,” Viribay told Runner’s World. “We’ve measured oxidation and performance with pro world tour cyclists and that’s the quantity we’ve estimated as the best one. Although I think that there could be no limit in this sense, as far as we know now, 120 is the most suitable target.”
As evidence, Viribay and a team of Spanish researchers compared the effects of various carbohydrate intakes, including 120 grams an hour, 90 grams an hour, and 60 grams an hour, in 20 elite male ultra endurance athletes running a mountain marathon that included 6,500 feet of climbing.
The researchers asked the runners to rate their perceived exertion, analyzed their heart rate data and exertion levels, and screened several markers of muscle damage including creatine kinase (CK), lactate dehydrogenase (LDH), glutamic oxaloacetic transaminase (GOT), urea, and creatinine after they were done.
The total internal exercise load—how much biological stress the runners experienced—and muscle damage was significantly lower in the runners who ate 120 grams of carbs per hour compared to their peers who ate 60 or 90 grams of carbs per hour during the competition.
The researchers suspect the higher carbs benefited the runners in part by keeping muscle glycogen stores at optimum amounts to limit fatigue and damage.
But whatever you do, do not line up for your next endurance endeavor and start taking five gels an hour in hopes of nailing a personal best. (For context, that would be 20 gels over the course of a 4-hour marathon, oof!) Without proper preparation, you’re asking for some serious GI distress.
The runners in this study were not only highly-experienced, elite-level athletes, but more importantly, they all had performed specific gut training leading into the experiment. During this gut training, the runners needed to have used 90 grams of carbs per hour at least two days a week in the four weeks leading up to the marathon in order to train their intestinal tract to increase its tolerance and absorption capacity.
That’s something Viribay believes everyone, not just elite athletes, can do.
“Starting from almost zero, our experience tells us that in six to eight weeks, three sessions per week, an athlete could tolerate higher intakes than 90 to 100 grams per hour,” Viribay says.
Though response and tolerance to all those carbs varies from person to person, everyone can eventually adapt; it just might take longer for some people to work up to those higher amounts, he says.
For the best results, eat foods with mixed carbohydrate sources including glucose (i.e. maltodextrin or dextrose) and fructose or sucrose (a combination of glucose and fructose), because your gut can only absorb so much of any particular sugar type at one time.
And be sure to give yourself plenty of flavor options, including salty and savory along with sweet. Though the runners in the very high carb group had no GI issues outside of saying they felt full, the constant assault of sweetness got to them, and some reported that flavor fatigue made it tough to keep getting the carbs in.
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