Why do sports drinks mix glucose and fructose?
Glucose and fructose cross the intestinal wall by different transporters, so taking both together roughly doubles the carbohydrate you can absorb per hour.
Glucose uses SGLT1, which saturates near 1 g/min. Fructose uses GLUT5, an entirely separate transporter that glucose does not compete for. Feeding both at once therefore adds two independent absorption channels instead of over-filling one, and total delivery rises to roughly 1.5 g/min — around 90 g/hr — with the best-adapted athletes reaching about 2 g/min.
The practical consequence is that the ratio on the label matters. Products aim for something between 1:0.8 and 2:1 glucose to fructose, which loads both transporters near capacity without leaving a surplus of either. This is why almost every modern gel and drink lists two sugar sources: it is a transport-physiology decision, not a flavour one.
Fructose has a second, less obvious advantage: the liver takes it up preferentially, which helps maintain liver glycogen and blood glucose late in a long race. It also has a well-earned reputation for causing gut distress in large single doses, which is precisely why it works better as part of a mix than on its own.
Key numbers
| Combined ceiling | ~1.5 g/min | about 90 g/hr |
|---|---|---|
| Elite trained ceiling | ~2.0 g/min | about 120 g/hr |
| Typical product ratio | 1:0.8 to 2:1 | glucose to fructose |
Work it out for yourself
Substrate & time-to-exhaustion calculator — Compare glucose-only and dual-transport fuelling on your own tank.
Frequently asked questions
What is the best glucose-to-fructose ratio?
Somewhere between 1:0.8 and 2:1 glucose to fructose. The exact figure matters far less than taking both at all — the jump from glucose-only to any sensible mix is much larger than the difference between mixes.
Is fructose bad for your stomach during a race?
Large fructose-only doses are poorly tolerated by many people. In a glucose-fructose mix at trained intake rates it is generally well tolerated, and the mix is usually gentler than an equivalent amount of glucose alone, because less sugar sits unabsorbed.
Sources
- Jentjens & Jeukendrup (2005). High rates of exogenous carbohydrate oxidation from a mixture of glucose and fructose. British Journal of Nutrition.
- Jeukendrup (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine.
Related explainers
Glossary: Dual Transport (Glc+Frc), SGLT1