Elite Endurance Fueling Doubles: New Science Pushes Carb Intake to 120 Grams Per Hour

For decades, endurance athletes operated under a strict biological speed limit. Sports nutritionists universally advised cyclists, marathoners, and triathletes to cap their mid-race fueling at 90 grams of carbohydrates per hour.

The logic was simple: the human digestive system was thought to be physically incapable of processing any more sugar than that. Forcing more gels or sports drinks down the hatch would not make an athlete faster; it would only leave them doubled over with severe gastrointestinal distress on the side of the road.

But over the last few years, a "carbolution" has swept through professional endurance sports. Driven by new formulations and aggressive gut-training protocols, elite athletes in the Tour de France and major marathons are now routinely consuming 120 grams of carbohydrates per hour—and sometimes pushing as high as 150 grams.

This massive influx of energy has been credited with powering the explosive, long-range attacks seen in modern professional cycling, effectively banishing the dreaded "bonk" from the peloton. But the shift from 90 to 120 grams per hour is not just a matter of eating more; it relies on a deep understanding of intestinal transport mechanisms.

To understand the new 120-gram ceiling, one must look at how the gut absorbs sugar. When an athlete consumes pure glucose—the most common simple sugar in sports drinks—it relies on a specific intestinal transporter protein called SGLT1 to cross from the gut into the bloodstream.

SGLT1 is highly effective, but it has a hard physiological bottleneck. It maxes out at a transport rate of roughly 60 grams per hour. If an athlete consumes 80 grams of pure glucose, the excess 20 grams simply sits in the gut, fermenting and drawing in water, which leads to bloating, nausea, and diarrhea.

In the early 2000s, scientists discovered a workaround: dual-source carbohydrates. Fructose, the sugar found in fruit, uses an entirely different transporter protein called GLUT5. By combining 60 grams of glucose with 30 grams of fructose, athletes could bypass the SGLT1 traffic jam and absorb 90 grams of total carbohydrate per hour. For years, this 2:1 glucose-to-fructose ratio was considered the absolute gold standard.

The leap to 120 grams per hour required tweaking that ratio and training the body to handle it. Modern high-carb products now utilize a 1:0.8 or even a 1:1 ratio of glucose to fructose, maximizing the capacity of both transport pathways simultaneously. But the real secret is a physiological adaptation known as "gut training."

The gut is highly adaptable. By progressively exposing the digestive system to higher carbohydrate loads during training sessions, athletes can actually force their bodies to upregulate—or increase the number of—SGLT1 and GLUT5 transporter proteins along the intestinal wall. A volume of sugar that would cause severe cramping in an untrained amateur is comfortably absorbed by a World Tour cyclist who has spent months stretching their digestive capacity.

The benefits of this extreme fueling strategy extend beyond simply providing more immediate energy. A landmark 2020 study led by performance nutritionist Aitor Viribay Morales tested elite runners during a grueling mountain marathon, comparing intakes of 60, 90, and 120 grams per hour.

The researchers found that the 120-gram group did not just maintain their power output; they experienced significantly less exercise-induced muscle damage. Biomarkers of muscle breakdown, such as creatine kinase and lactate dehydrogenase, were drastically lower 24 hours after the race in the high-carb group compared to those who consumed 60 or 90 grams.

"If you can consume 120 grams of carbs per hour in the race, you won't only perform better on the day, you will not have to eat such an extreme amount of food afterwards to recover," explains Amaia Martioda, team nutritionist for EF Pro Cycling. This accelerated recovery is a massive competitive advantage in multi-day stage races like the Tour de France.

Recent 2025 data further supports the metabolic advantages. A study on elite marathoners found that pushing intake to 120 grams per hour using a 1:1 ratio increased the rate of exogenous carbohydrate oxidation—meaning the athletes were successfully burning the fuel they ingested—and improved their overall running economy by reducing oxygen cost.

However, the 120-gram revolution is not without its skeptics. Some sports scientists caution that while the gut can be trained to tolerate 120 grams, it does not automatically translate to faster race times for everyone.

Critics point out that flooding the system with exogenous carbohydrates might simply prompt the body to burn more sugar and less fat, potentially accelerating the depletion of precious muscle glycogen stores rather than sparing them. In highly controlled studies, the performance gap between 90 grams and 120 grams is often marginal, even if the recovery benefits are clear.[1]

Furthermore, practical coaches warn that amateur athletes are misapplying the science. A professional cyclist racing a Grand Tour stage burns up to 1,200 calories an hour and relies almost entirely on carbohydrates. A recreational rider on a moderate weekend loop might only burn 500 calories. Attempting to force down 120 grams of sugar—roughly 480 calories—during a low-intensity ride is a recipe for severe stomach aches and unwanted weight gain.[2]

The consensus among nutritionists is that carbohydrate intake must scale with both duration and intensity. For rides under 90 minutes, 30 to 60 grams per hour is plenty. The 90-to-120-gram protocol is strictly a high-performance tool, reserved for intense racing or training sessions lasting longer than three hours.[2]

Ultimately, the "carbolution" has proven that the human body is far more adaptable than previously thought. The 90-gram ceiling has been permanently shattered, but reaching the new 120-gram frontier requires treating the digestive system like any other muscle: it must be trained, tested, and respected.