Glucose + fructose: how to absorb more carbs per hour
Why a glucose–fructose mix raises the carbohydrate ceiling from ~60 to 90+ g/h, and how the sugar ratio is built into Training Endurance gels.
Running out of energy on a long effort is almost never "ate too little" — it's "didn't absorb it." The carbohydrate ceiling is limited by transport in the gut, not by the stomach. And it can be nearly doubled by mixing the sugars correctly.
The bottleneck — transporters
Glucose is absorbed via the SGLT1 transporter, which saturates at roughly 60 g/h. Whatever you eat beyond that won't reach the blood — the excess stays in the gut, pulls in water and causes the familiar discomfort on the move.
Fructose takes a different route — the GLUT5 transporter. That's a separate channel that doesn't compete with the glucose one.
Why the mix works
Feed glucose and fructose together and both routes run at once, lifting the combined ceiling to 90 g/h and beyond. Hence the "magic" ratios on the label:
- 1:0.8 — the classic for most races;
- 2:1 — when the emphasis is on glucose uptake speed;
- high-carb blends for very long distances.
The key isn't the exact number — it's that the second sugar opens a second transporter.
How much, in practice
Aim for a target rate, not "eat more":
- up to ~1 h — water and electrolytes are often enough;
- 1–2.5 h — roughly 60–90 g/h;
- 3 h and longer — 90+ g/h, where a glucose–fructose mix is mandatory.
That then translates into a number of gels per hour for your serving size. The gut is trainable, too — absorption improves with regular fueling practice in training.
Takeaways
- The ceiling is set by transport, not the stomach.
- One sugar → ~60 g/h; a glucose + fructose mix → 90+ g/h.
- Train your gut: practice race fueling in training.
