Don't Be the 31%: Your Gut Training Journey to Ironman Race Day

You trained for months. Your legs were ready. Then, somewhere on the bike, your stomach wasn't.

If that sounds familiar, you are not unusual. Stomach trouble is one of the most common race-day problems in long-course triathlon (Pfeiffer 2012; Jeukendrup 2000; de Oliveira 2014). It is also one of the few race-day problems you can train for in advance. Not with a new gel. With a process.

This post walks through that process as Point8 guides it: a gut-training journey from a first test to a race-day plan built on what your own stomach has shown it can handle.

What one study found about stomach trouble in Ironman

Let's start with the number that gets people's attention.

In 2012, a research group led by Beate Pfeiffer and Asker Jeukendrup collected intake and symptom data from 221 endurance athletes at competitive events. Serious gastrointestinal symptoms were most common in Ironman races, reported by about 31% of athletes (Pfeiffer B, Stellingwerff T, Hodgson AB, Randell RK, Pöttgen K, Res P, Jeukendrup AE. Nutritional intake and gastrointestinal problems during competitive endurance events. Med Sci Sports Exerc 2012;44(2):344-351).

Two honest caveats. This is an observational study, not a controlled trial, so it describes what those athletes reported, not a law of the sport. And "about 31%" is one study's finding, not a prediction for you.

Still, the pattern is hard to ignore. The longer the event, the more hours your gut has to handle fuel at race effort, and the more athletes reported trouble.

Why the gut is the part of fueling most athletes never train

Here is the thing most race-day fueling advice skips.

Fueling well during long events is one of the best-supported ways to perform better (Ramos-Campo 2023; Stellingwerff 2014; Thomas 2016 (ACSM)). Sports-nutrition guidelines suggest up to 90 g/h for events longer than 2.5 hours, using a glucose + fructose mix. Your number depends on what your gut can handle (Jeukendrup 2014; Thomas 2016 (ACSM); Morton 2026).

That last sentence is the whole problem. A guideline tells you what a race asks for. It cannot tell you what your stomach will tolerate on a hot bike leg in hour four. Many athletes find that out for the first time on race day.

The good news is that the gut responds to practice. Training your gut with Point8 follows the approach shown in controlled studies to reduce stomach discomfort during exercise (Martinez 2023; Costa 2017; Miall 2018). Consistent fueling in training, not just on race day, builds your fueling tolerance (Cox 2010; Jeukendrup 2017).

Fuel calculators tell you what to take today. Point8 trains what your gut can take.

The gut-training journey, step by step

Point8 turns gut training into a sequence of small, logged steps. You always know which step you are on, what it asks of you, and why. Here is what each one looks like for an age-group athlete.

Step 1: Baseline. Find your starting number

Everything starts with a Fuel Capacity Test: a steady ride or run at a race-like fueling rate, long enough for your stomach to show its hand.

Why that long? The Fuel Capacity Test lasts 2 to 3 hours because that's how long it takes to see how your gut handles a race-like rate (Jeukendrup 2004; Podlogar 2022; Hearris 2022). A one-hour session tells you very little about hour four.

The result is a starting number in carbs per hour. Not a guess from a chart. Yours. If you've had stomach trouble before, Point8 starts you more conservatively (Pfeiffer 2012; Zhao 2025).

Step 2: Build. Raise the rate in small steps

From the baseline, you raise your fueling rate gradually, session by session, inside the long rides and runs you are already doing. Point8 sets the rate for each session. You fuel, you finish, and you answer one short question.

Rate your stomach 0 to 10 after each session; it takes seconds (Gaskell 2019; Pfeiffer 2012). That check-in is the heart of the system. It is how Point8 learns what your stomach did with that rate, in those conditions, on that day. A good session earns the next step. A rough session tells the app to hold or ease off. Progression is gradual, based on how your stomach responded.

A stomach that struggled is not a failure. It is data. Point8 is built to read it that way, and so should you.

Point8 is in beta. Join the Point8 beta to train your fueling capacity before race day.

Step 3: Prove. Hold the rate until it is demonstrated

Handling a rate once is a good day. Handling it comfortably across repeated sessions is capacity.

That is the difference Point8 draws between a rate you have tried and a rate you have demonstrated. Once you have held a rate comfortably over a set of sessions, it becomes part of your demonstrated fueling capacity: the number the app will trust when it builds your race plan. Point8 keeps the record of what your gut handled, and builds your race plan only from what you've practised.

One hero number. One line explaining it. That is deliberate. On the Progress screen you see what you have demonstrated, what your race still asks for, and the time you have left to close the gap.

Step 4: Validate. Rehearse it over race distance

A 70.3 bike leg is not a two-hour training ride, and an Ironman bike leg is a different animal again. So before race day, Point8 asks you to hold your demonstrated rate on a long ride, at race-like intake, for something close to the duration of the leg.

Think of it as a dress rehearsal for your stomach. It is where you learn whether a rate that felt fine at hour two still feels fine at hour five, with the same kit you plan to carry on the day. If it does, you go to the start line knowing, not hoping.

Step 5: Conditions. Make the number hold up on the day

A number demonstrated on a cool indoor trainer is not yet a race-day number. Point8 tracks the conditions you have covered and asks you to practise in the ones you have not.

• Heat. Hot races are harder on your gut, so Point8 adjusts your plan for the forecast (Snipe 2018; Jentjens 2002; Mougin 2025; McCubbin 2020). A warm-weather session shows what you can actually count on if race day is hot.
• Race effort. Race effort is harder on your gut than easy training, so Point8 tests both (Costa 2017 (APT); van Wijck 2011; ter Steege 2012). Fueling at Zone 2 and fueling at race intensity are two different skills.
• Run versus bike. Running is tougher on the stomach than riding, so your run capacity is tracked separately (Peters 1999; Rehrer 1991; de Oliveira 2014). Your bike number does not automatically transfer to the marathon.

As you cover each condition, the app ticks it off. Each tick is one fewer surprise waiting for you on race morning.

Step 6: Race-ready. A plan built from what you have demonstrated

The final step is the one most fueling tools start with: the race-day plan. The difference is what it is built from.

Your Point8 race plan starts from the fueling capacity you have demonstrated in training. It then adjusts for the forecast (Snipe 2018; Jentjens 2002; Mougin 2025; McCubbin 2020) and for effort. It also allows for nerves: race-day nerves can affect your stomach and your fueling, so Point8 builds in a margin (Wilson 2021; Lanpir 2025).

You choose how much risk you want to carry. Safe leans toward comfort and keeps your intake further inside what you have demonstrated. Balanced sits in the middle. PR leans toward performance and takes you closer to the edge of what you have shown you can handle. Same evidence, your call.

The plan works offline, so it is there at the start line whether or not the race village has signal.

Patience is part of the method

The gut adapts over weeks, not days. Studies saw improvements in as little as two weeks of consistent practice; most athletes build over several weeks (Costa 2017; Miall 2018; Martinez 2023). Point8 is designed to be used across a training block, not the week before your race.

Patience also means knowing when to stop pushing. Mild discomfort while adapting is common. Vomiting, diarrhoea or severe cramps are a different category. If severe symptoms keep happening, Point8 pauses progression and suggests seeing a professional (Costa 2025 (SDA); Costa 2017 (APT)). The app will not keep nudging you upward through repeated bad sessions, and it will not shame you for them.

A common story we hear

Consider a composite, illustrative athlete: the age-grouper who fades on the run. Strong bike, solid training, and every long-course race ends the same way, walking the back half of the marathon with a stomach that has shut the door on fuel. She has tried new gels, fewer gels, more water, less water. Each race is a fresh experiment with a sample size of one.

What changes with a journey like the one above is not the gel. It is that every long session before the race becomes part of the experiment, logged and checked, so the race-day plan is the last step of a sequence rather than the first and only test. This is a composite story, not a result, and it is not a promise. But it is the shape of the problem gut training is built to address.

What this may do for you

Keep the claims honest. Nothing here is medical advice, and no app can promise you a clean race. What the evidence supports is narrower and more useful than that.

• Fueling well during long events is one of the best-supported ways to perform better (Ramos-Campo 2023; Stellingwerff 2014; Thomas 2016 (ACSM)).
• Training your gut with Point8 follows the approach shown in controlled studies to reduce stomach discomfort during exercise (Martinez 2023; Costa 2017; Miall 2018).
• Consistent fueling in training, not just on race day, builds your fueling tolerance (Cox 2010; Jeukendrup 2017).

Put together: a structured journey may reduce the chance that you are one of the athletes whose race is decided by their stomach. That is the goal.

Built on published sports-nutrition research. Personalized from your own training sessions.

FAQ

How many carbs per hour should I take in an Ironman?

Sports-nutrition guidelines suggest up to 90 g/h for events longer than 2.5 hours, using a glucose + fructose mix. Your number depends on what your gut can handle (Jeukendrup 2014; Thomas 2016 (ACSM); Morton 2026). Point8 sets your race target from the event duration guidelines used by major sports-nutrition bodies and then trains you toward it from your own starting point.

Can you really train your gut?

Training your gut with Point8 follows the approach shown in controlled studies to reduce stomach discomfort during exercise (Martinez 2023; Costa 2017; Miall 2018). Consistent fueling in training, not just on race day, builds your fueling tolerance (Cox 2010; Jeukendrup 2017).

How long does gut training take?

Studies saw improvements in as little as two weeks of consistent practice; most athletes build over several weeks (Costa 2017; Miall 2018; Martinez 2023). Plan for it across a training block.

What if I get stomach trouble during a training session?

Log it in the check-in. A stomach that struggled is data, not a flaw, and the next session is adjusted accordingly. If severe symptoms keep happening, Point8 pauses progression and suggests seeing a professional (Costa 2025 (SDA); Costa 2017 (APT)).