Gut Training For Ultras: Why Your Stomach Needs Training Too

Most ultrarunners spend months training their legs, lungs, and heart.

But there’s another system that needs to show up on race day too: your gut.

If you’ve ever dealt with nausea, cramps, or a slightly panicked dash for the bushes mid-race… you’re definitely not alone.

Studies suggest up to half of endurance athletes experience gastrointestinal issues during long events, and ultrarunners tend to report more symptoms than pretty much any other sport.

The good news? A lot of this can be improved (or avoided altogether) with something called gut training.

Why the Gut Struggles During Ultras

During long efforts, your body shifts blood flow towards working muscles and your skin (to help regulate temperature).

Which means less blood goes to your digestive system. And that makes it harder to process food and fluids.

Now add in the realities of ultra racing:

• Frequent gels

• Sports drinks

• Eating while moving

• Dehydration

• Hours of continuous impact

• Trying whatever looks vaguely appealing at aid stations

Yeah… it’s not that surprising your gut sometimes throws a bit of a wobble.

Plan Your Nutrition. Train Your Gut.

At the sharp end of the sport, we’re seeing athletes taking on huge amounts of carbs, sometimes 120g+ per hour. But that tolerance doesn’t just happen.

Their race-day nutrition is:

• Planned

• Practised

• And their gut is trained to handle it

That doesn’t mean you need to hit those numbers. It just means: find what works for you (more on that below).

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Key Principles to Get It Right

Figure Out Your Race Logistics

How many aid stations are there? What food’s available? Can you have crew or pacers?

Knowing this ahead of time helps you figure out how much you need to carry and what’s realistic to rely on.

Find What You Like (and What You Don’t)

There’s a lot out there, drinks, gels, chews, real food.

Find what works for you:

• Too many options = decision fatigue every time you need to eat

• Too few = flavour fatigue (that tenth gel in 5 hours can be a struggle)

Mix up with flavours and textures so things still go down easily hours into the race.

Once you’ve got your go-to options, start using them in training - that’s where gut training really begins.

Build Carbohydrate Intake Gradually

Now you’ve got your products sorted, it’s time to practise. Start with what feels comfortable, then build slowly over several weeks. For example:

• Begin with one gel per hour

• Gradually increase

You’re looking for that sweet spot where you’re fuelling well and your stomach’s still happy

By the end of your training block, fuelling shouldn’t feel like a stress. It should feel automatic.

Simulate Race Conditions

Your gut doesn’t behave the same in every situation, so test things properly. Try fuelling at race effort. See how things feel in warmer temperatures. Notice if certain terrains (like long descents) make it harder to eat.

The more you learn in training, the fewer surprises on race day.

Try to Avoid Anything New on Race Day

This is a classic mistake. A lot of stomach issues come from sudden changes in fuelling.

Instead, your race-day nutrition should feel familiar, routine, and already tested dozens of times

The Takeaway

Your gut is a big part of endurance performance.

Ignore it… and race day can turn into a battle with nausea, cramps, and regret.

Train it… and fuelling just becomes another part of running strong for hours.

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Special thanks to Jamie Pugh for his contribution to this article.

Dr Jamie Pugh is an applied sport and exercise physiologist and performance nutrition specialist. His academic training includes a PhD focused on applied aspects of sports nutrition and metabolism, and he has worked with elite and international endurance athletes within athletics, ultramarathon running, and professional cycling.