Why Does My Gut Stop Working During Ultra-Cycling Racing?

You can have the perfect ultra-cycling race nutrition plan.

The right foods.
The right quantities.
The right timing.

And then your gut decides it isn’t playing.

For an ultra-endurance cyclist, that can be the difference between riding strongly through the night and watching the race slowly unravel.

Gastrointestinal function is one of the things I think about most when I’m planning our fuel strategy for a multi-day race.

Because the challenge isn’t simply getting enough fuel into the rider.

It’s getting enough fuel into a body that is cycling for days, sleeping very little, sitting in one position for hours at a time, dealing with heat or cold, and continually prioritising the demands of working muscles.

The nutrition strategy can be brilliant.

But if the gut can’t deliver it, the strategy doesn’t matter.

Why does my gut struggle during ultra-endurance racing?

There isn’t usually one single reason.

It’s a combination of physiological stress, prolonged exercise, body position, fuelling demands, hydration, environmental conditions and, importantly, the individual athlete.

Here are five of the things I think about when I’m planning for an ultra-endurance race.

1. Your gut has a big job to do

Think about your gastrointestinal tract as a remarkably sophisticated processing system.

Food has to be broken down, moved through the digestive system and ultimately absorbed so that the nutrients and energy it contains can be used by the body.

That process takes time. It requires blood flow and a functioning digestive system.

Most of the time, we barely notice any of it.

During an ultra-endurance race, however, we’re asking the body to do something quite different.

We’re asking it to digest and absorb fuel while simultaneously producing energy for hours — and sometimes days — of continuous exercise.

That’s a very different physiological environment.

2. You’re asking your digestive system to work while you’re riding

An ultra cyclist doesn’t spend much time standing up, walking around or changing position.

They’re sitting on a bike for hour after hour, often through the night and sometimes for several consecutive days.

The body is also dealing with the movement and vibration of the bike, changes in posture and the physical demands of maintaining position and control.

None of this means that food simply gets “stuck” because you’re sitting down.

But prolonged exercise and body position can influence gastrointestinal function and motility, and the longer the race continues, the more significant that becomes.

And there’s very little opportunity to give the system a proper break, which is why, when you have a chance to stretch out – take it!

3. Blood flow is being prioritised elsewhere

During exercise, the body has to make decisions about where blood is needed most.

Working muscles need oxygen and nutrients.

Your skin may need increased blood flow to help regulate body temperature.

Your cardiovascular system is working hard to keep everything going.

At the same time, the digestive system needs adequate blood flow to support digestion and absorption.

As exercise intensity increases, blood flow can be redistributed away from the gastrointestinal tract.

Heat makes this even more challenging because thermoregulation becomes an increasingly important demand.

This is one reason why gastrointestinal problems can become particularly troublesome when an athlete is working hard in hot conditions.

4. You’re asking the gut to process fuel for an extraordinary energy demand

An ultra-endurance athlete can burn a huge amount of energy over the course of a race.

And unlike a shorter event, there is no option to simply rely on the carbohydrate that is stored in the body, in the form of glycogen, for the duration of the effort.

Even if you’re relying heavily on body fat to create energy, you still need to be able to process carbohydrate through the gut because fat oxidation alone cannot meet the energy demands of sustained higher-intensity exercise.

Fuel, therefore, has to keep coming in.

We also know that the gut cannot absorb every calorie the athlete is burning, so ultra-endurance nutrition is never about replacing every calorie expended. It’s about supplying enough carbohydrate and fluid to support performance while staying within what the individual athlete can tolerate.

That means eating and drinking while riding, often when appetite is low, fatigue is high and the body is already under considerable physiological stress.

The challenge is finding the amount and combination of carbohydrate, fluid and other foods that an individual athlete can actually tolerate and absorb while exercising.

Too little fuel creates one set of problems.

Too much, or the wrong combination at the wrong time, can create another.

This is why race nutrition isn’t simply a matter of calculating how many calories an athlete needs and dividing them across the hours of a race.

The gut has to be able to handle the plan.

5. Your brain and your gut are very closely connected

And then there’s stress.

The gut doesn’t operate independently from the rest of you.

The gastrointestinal system and nervous system are closely connected through what is often described as the gut-brain axis.

Which makes perfect sense when you think about what an ultra-endurance race actually involves.

Physical and mental stress, sleep deprivation and fatigue.

Weather, time pressure and uncertainty.

Decision-making when you’re exhausted.

All of these things can influence gastrointestinal function.

And that’s why an athlete can start a race feeling completely comfortable with their nutrition, only to find that several hours, or several days, later, things aren’t working in quite the same way.

Bloating, nausea, reflux, diarrhoea, constipation or a complete loss of appetite – none of them are particularly helpful when you’ve got another 500 miles to ride.

What happens when ultra-endurance race nutrition goes wrong?

This is where things become serious.

If an athlete can’t tolerate or absorb enough fuel, they have fewer options as the race continues.

They may start eating less and riding harder than they can support.

Energy levels fall.

Pace drops.

Decision-making becomes harder.

Fatigue increases.

And the temptation is often to try to solve the problem by putting more food into a gut that is already struggling.

That can make things worse.

Eventually, the athlete may have to slow down significantly, take an extended rest to allow things to settle or, in the worst-case scenario, withdraw from the race.

And this is why I don’t see race nutrition as simply a question of what an athlete should eat.

It’s a system.

It has to account for the athlete, the event, the duration, the intensity, the conditions, the likely demands on the body, and crucially what that athlete has practised and learned to tolerate.

So how do you prevent your gut from stopping?

You can’t guarantee perfect gastrointestinal function in an ultra-endurance race.

There are too many variables.

But you can give yourself a much better chance.

Practise your nutrition before race day.

Don’t wait until the big event to discover that your carefully designed strategy doesn’t work when you’re riding for 12, 24 or 48 hours.

Build your tolerance gradually.

The gut is adaptable. What you can comfortably consume during exercise can change with appropriate training and repeated exposure.

Match your nutrition to the race.

A six-hour event, a 24-hour race and a six-day ultra are not the same nutritional problem.

Pay attention to the whole picture.

Food isn’t the only variable. Hydration, intensity, heat, cold, sleep, stress and pacing can all influence how well the gut behaves.

And perhaps most importantly:

Have a plan, but be prepared to adjust it.

Ultra-endurance racing rarely follows the script.

Your nutrition strategy needs enough structure to keep you moving towards your nutritional requirements, but enough flexibility to respond when your body, the weather or the race throws something unexpected at you.

Why this keeps me awake at night

It’s probably why race nutrition planning can be a slightly obsessive process for me.

Because I know how many things can change once the rider leaves the start line.

I can sit down with Joe’s race plan and think through the demands of the course, the expected duration, the weather, the intensity and the opportunities to eat and drink.

I can build the strategy, practise and refine it.

And then, at 2am, my brain can still decide to start this conversation:

Okay. He can ride for 35 hours with minimal stops.

He’s going to push hard from the start.

What if the weather turns cold?

What if it gets hotter than expected?

What if he needs more energy but his gut can’t handle it?

How do we get enough fuel in without overloading the system?

How do we keep him hydrated?

How do we keep him warm?

What if…?

The realities of racing ultra

This is the reality of ultra-endurance race nutrition.

You don’t just plan what goes into the athlete.

You plan for what might happen to the athlete.

And that’s why, after years of working with endurance athletes, I still treat the gut with a healthy amount of respect.

Because when the gut is working, it can support an extraordinary performance.

When it isn’t…

Well, that’s when things can get very interesting.

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If you’re preparing for an ultra-endurance event, your nutrition strategy deserves as much attention as your training.

I work with athletes to build practical, personalised nutrition strategies that support performance, and work in the real world.

If you want your nutrition to work as hard as you do, let’s talk.