Gut Training Basics

Teaching your stomach to handle carbs, effort and race day nerves

Most athletes think about training legs, lungs and maybe the brain a bit. Almost no one thinks about training the gut – until the day it stages a protest halfway through a race.

Stomach cramps. Urgent toilet stops. Nausea. That horrible “everything I eat just sits there” feeling. All of that gets blamed on “a sensitive stomach” or “that one gel”, but often the real issue is much simpler: the gut has never been asked to do, in training, what you’re asking of it on race day.

Gut training is about fixing that. It’s the process of gently teaching your stomach and intestines to handle more carbs, more fluid and more intensity, so you can actually use the fuel you’re putting in without everything kicking off.

You don’t need a lab and test tubes. You just need a bit of structure, some patience, and the acceptance that “practice in training” isn’t just about pacing – it’s about fuelling too.

Why the gut struggles on race day

On paper, it looks simple. You’ve read that you should take on X grams of carbs per hour, so you buy the gels and drinks, turn up to the race, and start taking them like the chart says. Then, 90 minutes in, your stomach starts making decisions without consulting you.

What’s going on?

When you exercise, blood is prioritised to working muscles, skin (to help cool you down), and your heart and brain. The gut gets less. Digestion slows. On top of that, race-day nerves ramp up stress hormones, which also don’t exactly encourage calm, relaxed digestion.

If, on top of that, you suddenly ask your gut to:

Deal with higher carb intakes than it’s used to

Process products you’ve barely tried

Keep up while you’re working harder than in training

…it’s no surprise it throws a tantrum.

The point of gut training is to reduce the surprise. If your stomach has seen those amounts, those products and that pattern of intake before, it’s far more likely to cope on the day.

Gut training is just… training

The good news is that your gut is adaptable. Just like your muscles learn to handle more mileage and your lungs learn to cope with more effort, your digestive system can get better at absorbing and moving carbs while you’re working.

Gut training isn’t a separate programme. You don’t need a special “gut day” on your plan. You simply build it into the long and key sessions you’re already doing by:

Starting to fuel earlier

Using the same types of products you plan to race with

Gradually nudging the amount of carbs and fluid up over time

Think of every long run, long ride and big brick as not just fitness work, but a dress rehearsal for what your gut needs to do on race day.

Start where you are, not where a chart says you should be

You might have seen numbers like “60–90g of carbs per hour” thrown around. Those can be useful targets for long, hard events – but they’re not where you have to start.

If you currently take on one gel in two hours and hate it, jumping straight to 80g of carbs per hour is a recipe for disaster.

A calmer approach:

Notice what you’re doing now: how often you fuel, what with, roughly how much.

On your next few long sessions, increase that just a little. One extra gel across the whole session. Slightly more sports drink. Half a bar or banana where you’d normally have nothing.

See how you feel – during and after. Stomach, energy, mood, recovery.

If that feels okay, you nudge things up again next time. Over a few weeks, you can work towards whatever intake you think will suit your event, without ambushing your gut.

The same goes for fluid and electrolytes. If you never drink on runs, start with a small bottle and a few sips every 15–20 minutes. If you always use plain water, slowly introduce an electrolyte tab and notice any difference.

Use your long sessions as experiments

The best place to train your gut is in the sessions that look most like your race demands: longer runs, longer rides, bricks, simulation days.

Pick one of those sessions and make it a fuelling test:

Eat the kind of breakfast you might have on race morning.

Use the same types of carbs you plan to eat or drink on race day – gels, chews, bars, sports drink, even on-course products if you know what they are.

Start fuelling early in the session – not at the point where you’re already struggling.

Aim for a realistic carb range for that workout (even if it’s lower than race-day targets) and stick to a pattern: for example, a small hit of fuel every 20–30 minutes.

Then, afterwards, ask a few questions:

How did my stomach feel?

Did I feel more or less steady in energy compared to usual?

Did I feel wrecked afterwards, or surprisingly okay?

What, specifically, seemed to sit well or not well?

You’re not judging yourself. You’re gathering information. Next time, you adjust based on those answers: change the product, tweak the timing, nudge amounts up or down.

Do this three, four, five times over a training block and you’ll learn more about your gut than any generic guide can tell you.

Small tweaks that make a big difference

While you’re training the gut, a few simple habits help a lot:

Start fuelling early. Waiting until 60–90 minutes in to take your first gel makes life much harder. Your gut tends to cope better if you trickle fuel in from early on.

Break carbs into small, frequent hits. Rather than 40g in one go every hour, try 20g every 20–30 minutes. It’s often easier on the stomach.

Sip, don’t chug. Necking a whole bottle at once is more likely to give you the washing-machine feeling. Small, regular sips are friendlier.

Keep other variables steady. On test days, don’t also change your shoes, your route and your interval structure. Change fewer things so you know what’s causing what.

None of this is glamorous. But it’s how you calmly stretch your gut’s comfort zone over time.

When things go wrong (in training, not on race day)

You will have the odd session where your stomach complains. That doesn’t mean gut training isn’t for you. It just means you’ve found a line – which is exactly the point of doing this in training rather than in a race you’ve paid for.

If a session goes sideways, reflect on:

Did I increase the amount of carbs too much in one go?

Did I take big doses all at once instead of spreading them out?

Was I running or riding much harder than usual?

Did I eat something very heavy or high in fat shortly before?

Was it very hot, and did I drink loads of plain water without electrolytes?

Often, the fix is to dial back a step and try again: a bit less per hour, or a different product, or more spacing between doses, or a calmer pre-session meal. Over a few attempts, you’ll figure it out.

The key is not to give up at the first sign of discomfort and decide your gut is “just bad”. It’s a process – a slightly messy one, sometimes, but still a process.

Race-day confidence comes from repetition

The real advantage of gut training is the confidence it gives you.

By the time race week arrives, you want to be able to say:

“I’ve eaten this breakfast before key sessions and felt fine.”

“I’ve used these gels and drinks at this intensity and my stomach coped.”

“I know roughly how often to take fuel without waiting until I’m desperate.”

That quiet, lived-in knowledge does far more for your race than any last-minute fuelling tweak. It lowers stress, which in turn makes your gut happier. It means you can respond calmly if small things go off-script, because you know what your body usually does and what it needs.

Gut training basics boil down to this: don’t surprise your stomach on the day that matters most. Use your long sessions to slowly teach it what race day will feel like in terms of fuel, fluid and timing. Start where you are, nudge things up bit by bit, and learn from each experiment.

Do that, and your gut stops being an unpredictable saboteur and starts behaving more like part of the team – not perfect, not silent, but a lot less dramatic when you need it to perform.