If you started riding twenty years ago you were told 60 grams of carbohydrate an hour, and that was the end of the conversation. If you started last year you’ve probably seen 120 on a gel wrapper and assumed the sport had lost its mind.
Both numbers are real. What changed in between is worth understanding, because it decides whether you should be chasing the big one.
Why 60 was the ceiling
Glucose doesn’t cross your intestinal wall on its own. It rides a transporter called SGLT1, and there are only so many of them. Feed a rider more and more glucose during exercise and the amount they can actually burn from that drink flattens out around 60 grams an hour, about a gram a minute. Past that you’re not fueling, you’re just carrying it. Often unpleasantly.
That number held for years because it’s a hard physical limit, not a matter of trying harder.
The second door
Fructose uses a different transporter. Asker Jeukendrup’s group worked out that if you combine glucose and fructose you open two channels at once, and the amount of ingested carbohydrate you can oxidize jumps by as much as 65% over glucose alone. The ceiling wasn’t the gut, it was the single-door design.
That’s where 90 grams an hour comes from, and why sports drinks started listing ratios on the label. It’s the standing recommendation for efforts past about two and a half hours, and for most people it’s the useful target.
Where 120 came from
Then Viribay and colleagues went further, in the field, with elite mountain marathon runners taking 120, 90 or 60 grams an hour through an actual race. The 120 group came out with markedly lower markers of muscle damage. A companion study on a trail marathon found better neuromuscular function and a better return of high intensity running capacity afterward at 120 as well.
Those are small studies on elite athletes who had clearly practiced eating like that, and one race is not a training block. Treat 120 as evidence that the ceiling is higher than we thought rather than as a target for your Saturday ride.
The part nobody wants to hear
Your gut is trainable, and if you don’t train it, none of this applies to you. Jeukendrup made the case directly in 2017: transporter expression, gastric emptying and comfort all adapt to regular practice. Which means the athlete who reads about 120 grams an hour and tries it for the first time on race morning is going to spend the back half of the day looking for a hedge.
Practice it the way you practice intervals. Take your race fueling on long training days, push the rate up gradually across a block, and find your own edge somewhere well before you need it.
Fueling is durability
There’s a thread connecting this to the durability research. When Clark’s group looked at what happens to critical power during prolonged exercise, carbohydrate intake during the ride blunted the decline. Eating isn’t only about not bonking. It’s about which athlete shows up at hour four.
The rate should scale with the day. A 90 minute endurance ride doesn’t need 90 grams an hour. A six hour race at tempo needs everything you can absorb. Allure sizes carbohydrate, fluid and sodium per session against how long and how hard you’re actually going, so the number moves with the work instead of sitting there as a slogan you half remember.
Start at 60. Get comfortable. Work toward 90. Only chase 120 if you’re racing long enough that it changes the outcome, and only after your gut has agreed to it in training.
Sources
- Jeukendrup AE. Training the gut for athletes. Sports Med. 2017;47(Suppl 1):101-110.
- Jeukendrup AE. A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Med. 2014;44(Suppl 1):S25-S33.
- Viribay A, Arribalzaga S, Mielgo-Ayuso J, Castañeda-Babarro A, Seco-Calvo J, Urdampilleta A. Effects of 120 g/h of carbohydrates intake during a mountain marathon on exercise-induced muscle damage in elite runners. Nutrients. 2020;12(5):1367.
- Urdampilleta A, Arribalzaga S, Viribay A, et al. Effects of 120 vs. 60 and 90 g/h carbohydrate intake during a trail marathon on neuromuscular function and high intensity run capacity recovery. Nutrients. 2020;12(7):2094.
- Clark IE, Vanhatalo A, Thompson C, et al. Dynamics of the power-duration relationship during prolonged endurance exercise and influence of carbohydrate ingestion. J Appl Physiol. 2019;127(3):726-736.