90 g Carbs Per Hour: The Race-Day Fueling Guide

It's kilometer 30. Your legs are still holding, but the lights are going out – the world turns grey and the pace falls away.

Anyone who has ever gone long knows the wall. The tricky part: it rarely has anything to do with your fitness and almost always with your tank. Take in too few carbs during a race and sooner or later you'll be running on empty – no matter how clean your training was. The good news: fueling is a skill you can train like intervals.

Long sessions are your test lab: this is where you find out how many carbs your stomach can really handle.

Why your tank decides the race

Your body stores only around 400 to 500 grams of carbohydrates as glycogen – enough for roughly 90 to 120 minutes of intense effort. After that, every gram you take in from outside counts. For a long time, the rule of thumb capped intake at 60 grams per hour. The reason lies in the gut: glucose is absorbed via the SGLT1 transporter, and at about 60 grams per hour it is simply saturated. More glucose alone does nothing – it sits in your stomach and causes cramps rather than energy. As the Gatorade Sports Science Institute summarises based on the work of Asker Jeukendrup, this limit can be cleverly bypassed: combine glucose with fructose and you tap a second transport route (GLUT5) – and absorption rises significantly.

How to fuel right on race day

Theory is nice – but what does it mean for your next half marathon, marathon, or triathlon? Here is how to put it into practice:

• Count in grams, not gels: A typical gel delivers around 25 grams of carbs. So for 60 g/h you need one roughly every 25 minutes; for 90 g/h, one every 20 minutes plus a sports drink.
• Go for a glucose-fructose mix: Look for «maltodextrin and fructose» on the label or a stated 2:1 ratio. That is exactly what lifts your ceiling from 60 to 90 grams.
• Early and regular instead of late and large: Start within the first 30 minutes, not once the tank is empty. Small amounts every 15 to 20 minutes are gentler on your stomach than one big hit.
• Drink alongside: Concentrated gels need water to clear your stomach quickly. A sip or two with every gel helps prevent stomach and gut trouble.

The best fueling strategy is useless if you try it for the first time on race day.

The most common mistake: forgetting the gut

Many runners buy the right gel and still fall apart – because they never prepared their stomach for the volume. The gut is adaptable: studies show that carbohydrate absorption improves measurably within just two weeks of «gut training», while stomach and gut complaints decline. A study documented in the Journal of the International Society of Sports Nutrition confirms that targeted adaptation increases tolerance. In practice, according to TrainingPeaks, that means: dedicate one session per week to fueling training, start at around 30 g/h, and add about 10 grams every one to two weeks until you can handle your race-day amount without problems.

Test it under race conditions

If you want to test your strategy, you need a goal with real distance: at IRONMAN Switzerland in Thun on July 5, 2026, fueling decides seconds and hours – here every trained gel routine pays off. To keep your supplies within reach, kit with real pockets is worth it: the Driven Pace Performance Shorts hold gels securely against your body without chafing – so reaching for energy never knocks you out of rhythm.

The bottom line

Your tank decides whether the final kilometers fly or fall apart. Combining glucose and fructose lifts your ceiling from 60 to 90 grams per hour – but only if your gut plays along. Train your fueling as seriously as your tempo runs, start early in the race, and test everything beforehand. Then the wall stays where it belongs: behind you.

Give it a go and tag us on Instagram at @athlix.performance – we would love to see how you put your fueling strategy into action, and we will share the best posts with the community.