Learn · Fueling
Glucose and fructose: why the mix matters above 60 g/h
The short answer: up to about 60 grams of carbohydrate an hour, one kind of sugar is enough. Above that you need glucose and fructose together, usually two parts glucose to one part fructose. For intakes above 90 grams an hour, mixes closer to equal parts are being tried, with less evidence behind them.
Two ways in
Glucose and fructose cross the gut wall through different transporters. The glucose transporter, SGLT1, is saturated at around 60 grams per hour; past that point, more glucose does not get absorbed any faster 1. Glucose-based carbohydrates include maltodextrin, which many drink mixes are built on.
Fructose uses its own transporter. When riders in lab studies took glucose at the maximum rate plus fructose on top, they burned about 1.26 grams of carbohydrate per minute from their drinks, well above the roughly 1 gram per minute that glucose alone allows 1.
What the ratios mean
| Ratio (glucose : fructose) | Used for | Evidence |
|---|---|---|
| Glucose only | Up to about 60 g/h | Well established 1 |
| 2 : 1 | About 90 g/h on long rides | Well established 1 |
| 1 : 0.8 | Around 120 g/h | One small study in trained men 2 |
In that one study, 11 highly trained male cyclists absorbed and burned more carbohydrate at 120 grams an hour with a 1 : 0.8 mix than at 90 grams with 2 : 1, without more stomach complaints. It did not show that they rode faster, and it did not include women or less trained riders 2.
Reading a label
Sports products that are built for high intakes usually state their ratio. If yours does not, look at the ingredients: maltodextrin, glucose and dextrose are glucose; fructose is fructose; ordinary sugar (sucrose) is half of each. What matters is the mix across everything you take in an hour, not each product on its own.
Practise it
The gut adapts to high carbohydrate intakes with training 1. Try your race-day mix and amounts on long training rides, not for the first time at the start line.
The FondoLab fueling planner tells you which mix your target needs and warns you when you cross 60 and 90 grams an hour.
References
- Jeukendrup A (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine 44(Suppl 1):25–33. doi:10.1007/s40279-014-0148-z
- Podlogar T, Bokal Š, Cirnski S, Wallis GA (2022). Increased exogenous but unaltered endogenous carbohydrate oxidation with combined fructose-maltodextrin ingested at 120 g h−1 versus 90 g h−1 at different ratios. European Journal of Applied Physiology 122(11):2393–2401. doi:10.1007/s00421-022-05019-w