How to fuel your HYROX to minimise the risk of stomach upsets

FODMAPs are certain carbohydrates that aren’t always fully absorbed in the small intestine. They can draw additional water into the bowel and are then fermented by gut bacteria, which can contribute to bloating, gas, loose stools and urgency in susceptible people.

Jackson stresses that this isn’t about following a restrictive low-FODMAP diet all the time. Instead, it can be a short-term race strategy for someone who already knows their gut is sensitive.

Crucially, Jackson advises against responding to a fear of stomach problems by simply eating less. Carbohydrate is incredibly important because the aim is to maximise glycogen stores before an event rather than under-fuelling in an attempt to keep the gut completely empty.

Patel agrees that under-fuelling is one of the biggest mistakes she sees, particularly among women athletes.

“Good fuelling should provide energy without overwhelming the gut. The amount, timing and type of carbohydrate all matter—and the plan should always be well practised during training rather than introduced on competition day,” she says.

Jackson recommends choosing carbohydrate sources you already know you tolerate and that allow you to meet your fuelling needs without suddenly loading your gut with large amounts of poorly absorbed carbohydrates.

Your pre-race meal matters

Ideally, your main meal should be around three to four hours before HYROX, says Patel. She recommends choosing familiar, carbohydrate-rich foods with some protein that are relatively low in fat and fibre.

Porridge with yoghurt and banana, or rice with chicken, are examples of meals that could work, depending on your individual tolerance.

If you need to top up your energy stores closer to the start, Patel says a small carbohydrate-based snack one to two hours beforehand can be useful.

But this is not the time to try something new.

“Before competing, limit foods that are unusually high in fat, fibre or spice, as well as large meals, alcohol and highly concentrated sugary drinks,” says Patel.

Sugar alcohols, which can be found in some bars, gels and ‘diet’ products, can also cause bloating or diarrhoea.

Patel’s biggest piece of advice is simple: “Never experiment with a new supplement on race day.”

On race day: familiarity is your friend

Jackson says your pre-race meal shouldn’t be an experiment. She recommends eating foods and portion sizes you’ve already tested during training, giving yourself enough time to digest before the start.

The same applies to any last-minute snacks, drinks, gels or supplements. Just because something is marketed for sport doesn’t mean your gut will tolerate it.

Some gels, energy sachets, electrolyte powders and drinks can contain high-FODMAP ingredients or large amounts of certain sugars or sugar alcohols.

“I get athletes to practise with the exact products and quantities they intend to use on race day,” says Jackson.

Patel also recommends keeping a training and symptom diary to help identify individual triggers. She advises athletes to rehearse their breakfast, caffeine, hydration and race fuel under realistic conditions, including during high-intensity sessions.

She also recommends leaving enough time to use the bathroom before starting.

What about coffee and energy drinks?

Jackson says caffeine is another factor worth considering if you’re prone to bowel urgency. It can stimulate the gut in some people, so race morning probably isn’t the time to suddenly double your usual coffee intake or try a highly caffeinated pre-workout or energy drink.

That doesn’t necessarily mean caffeine needs to be avoided altogether. Individual tolerance is important. If caffeine is already part of your training routine and you know your digestive system copes well with it, that’s very different from introducing a new product or a larger dose on race day.

Patel agrees that caffeine can be an issue.

“It can stimulate the bowel and increase urgency, particularly in sensitive athletes or at higher doses. If you use it, establish your personal tolerance in training and remember that more is not necessarily better,” she says.

ILCE-7RM6 · f/2 · 1/1600s · 150mm · ISO2000

During HYROX: don’t overload your stomach

Jackson says how much fuel you need during the event will depend on factors including how long you expect to be competing and what you have eaten beforehand.

If you do use gels, sports drinks or other carbohydrate sources during HYROX, Jackson recommends using products you have already practised with in training.

The goal is to provide enough fuel to support performance without suddenly asking an already stressed digestive system to deal with something unfamiliar.

Patel stresses that gut tolerance and fuel requirements are highly individual. She warns against taking excessive gels without enough fluid, trying unfamiliar products or simply copying a fuelling strategy seen on social media.

The same principle applies to hydration.

Jackson says dehydration can contribute to gastrointestinal symptoms, but drinking a large volume at once may also leave you feeling uncomfortable. Practise your hydration strategy during training so you know what works for you.

Patel adds that dehydration can reduce blood flow to the gut and make digestive symptoms worse, particularly in warm conditions.

“Start well hydrated and sip fluids according to your individual needs,” she advises.

Train your gut – and your brain

Jackson says we need to train the gut-brain axis as well as the muscles.

Race-day nerves can affect the bowel. Stress and anticipation can alter gut motility and, for some people, that means looser stools or repeated trips to the toilet before the start.

Practising your race-day routine during training – the same breakfast, timings, fluids and sports nutrition – helps train the digestive system, but it can also make the whole routine feel familiar and reduce some of that race-day stress response.

Jackson also recommends using meditation on a daily basis throughout the year as a practical way of training your brain not to trigger your gut to move in response to stress.

Patel agrees that athletes can train their gut.

“Regularly practising the exact drinks, gels or foods you plan to use during competition can improve tolerance. Begin with small amounts during race-specific sessions and gradually increase them over several weeks,” she says.

Don’t simply eat less to avoid stomach problems

Jackson’s biggest advice is not to simply eat less before HYROX.

You need enough carbohydrate to perform and maintain your glycogen stores, while choosing foods, fluids and sports nutrition that your gut has already demonstrated it can handle.

Patel says one of the biggest mistakes she sees, particularly among women athletes, is under-fuelling. In relation to GI problems, she also highlights eating a heavy meal too close to the start, taking excessive gels without enough fluid, trying unfamiliar products and copying strategies from social media.

“Gut tolerance and fuel requirements are highly individual,” she says.

If bowel urgency, diarrhoea or leakage is happening repeatedly, don’t simply accept it as part of being an athlete. Persistent or worsening symptoms deserve proper assessment, particularly if you experience blood in your stool, significant abdominal pain, unexplained weight loss or a persistent change in bowel habit.

Kirsten Jackson is a Consultant Dietitian and founder of The IBS Dietitian.