Fuelling for endurance events

The limit is absorption, not appetite

You can only use carbohydrate as fast as you can move it out of the gut. A single transporter handles glucose, and it saturates at around sixty grams an hour however much you swallow. Everything past that sits in your intestine drawing water in, which is the mechanism behind most race-day stomach disasters.

Fructose uses a different transporter. Combine the two — glucose and fructose together, roughly two to one — and the ceiling lifts to about ninety grams an hour, with trained guts reaching higher still. This is why every modern sports drink and gel lists two sugars rather than one.

Match the intake to the duration

Under an hour, you do not need to fuel; you need to have eaten beforehand. One to two hours, thirty to sixty grams an hour is plenty. Beyond two and a half hours, sixty to ninety grams an hour is where the performance difference is made, and it is the range most amateurs never reach.

The failure mode is almost always under-fuelling early. Carbohydrate taken in the first hour, when you feel fine and cannot imagine needing it, is what keeps the third hour intact.

Train the gut like anything else

Absorption capacity adapts. Practising your race intake in training, at race intensity, for several weeks beforehand meaningfully improves both how much you tolerate and how comfortable it feels. A gut that has only ever seen water will not manage ninety grams an hour on the day.

Rehearse the exact products you will use. Race day is not the moment to discover that a particular gel does not agree with you.

• 01

  Start fuelling in the first hour, before you want to

  The common mistake
• 02

  Choose products with two sugars, not one

  Why it works
• 03

  Practise the exact race intake in training

  Gut training