How to start fixing it

For years, when athletes struggled with poor sleep, anxiety, repeated illness, IBS, or race-day stomach issues, we treated these as separate problems. Sleep coaches talked about sleep. Nutritionists talked about food. Coaches talked about pacing and training load.

But increasingly, one system keeps showing up at the centre of it all.

The gut.

In recent podcast episodes, I sat down with Harvey Fortis, a performance nutritionist and researcher completing his PhD at Liverpool John Moores University. Harvey also works with INEOS Cycling and Total Endurance Nutrition, so he sees first-hand how gut health influences performance at every level.

What became clear very quickly is this. The gut is not just about digestion. It plays a major role in how you sleep, how you handle stress, how often you get ill, and how well you tolerate training and racing. (Listen to part 1 of the podcast)

The gut is a control centre, not a food tube

Most people think of the gut as a stomach problem. Bloating, reflux, IBS, food intolerance.

In reality, the gut is an eight to nine metre system that houses trillions of microbes. These microbes act more like a community than a single organ. Harvey described it as a city within you, with workers, messengers, builders and, occasionally, troublemakers.

What surprised many listeners is that we host roughly the same number of bacterial cells as human cells. Even more striking, there are far more genes in those microbes than in our own body.

That matters because these microbes help regulate inflammation, immune function, hormone signalling, blood sugar control, and communication with the brain.

When the system works well, everything feels easier. When it does not, problems start to stack up.

Why poor gut health disrupts sleep and mood

One of the most powerful insights from the conversation was the gut brain connection.

Around 80 percent of communication between the gut and the brain travels upwards. That means your gut sends far more signals to your brain than your brain sends back.

This helps explain why poor gut health is linked with anxiety, low mood, brain fog, and poor sleep.

Eat late, eat poorly, or live under chronic stress and your gut never really switches off. You are effectively asking your digestive system to work a night shift. The result is lighter sleep, more wake-ups, and a nervous system that never fully down-regulates.

Over time, this becomes a vicious cycle. Poor sleep increases stress hormones like cortisol. Cortisol disrupts gut function. Gut disruption feeds back into sleep and mood.

Many people assume this is just part of ageing or modern life. In reality, it is often a gut issue hiding in plain sight.

Immunity, inflammation, and why you keep getting ill

Around 70 percent of your immune system is associated with the gut.

When gut integrity is compromised, fragments from inside the gut can leak into the bloodstream. This drives chronic low-grade inflammation.

That inflammation does not always show up as pain. More often it appears as fatigue, poor recovery, frequent colds, joint aches, or a general feeling of being run down.

If someone is missing training sessions regularly due to illness, I now look at gut health very early in the conversation.

Race-day GI distress is rarely just a race-day mistake

One of the most relatable insights for endurance athletes is this:

Most race-day stomach issues are not caused by a single gel or drink. They are caused by a gut that has not been supported day to day.

Athletes often obsess over carbohydrate grams per hour, but forget that the gut is a tissue that needs training and recovery like anything else.

You cannot neglect gut health for months, then ask it to perform under heat, dehydration, stress and high carbohydrate loads.

As Harvey put it, you need to build the structure first, then ask it to perform.

So how do you start fixing your gut?

The good news is that improving gut health is not about restriction. It is about inclusion.

A few simple principles make a big difference. (Listen to part 2 for practical tips on how to fix your gut)

Firstly, variety matters more than perfection. A diverse gut thrives on a diverse diet. Aim to increase the range of plants you eat across the week, not just the quantity. Different colours, different fibres, different sources.

Second, fibre feeds your microbes. Foods like oats, legumes, vegetables, fruit, onions, garlic and leeks provide the raw material your gut bacteria ferment into compounds that support immunity, metabolism and even brain function.

Third, fermented foods add helpful bacteria directly. Yoghurts, kefir, sauerkraut, kimchi, sourdough and kombucha can all play a role. You do not need all of them. One per day is a good starting point.

Fourthly, timing and volume matter. Many gut issues are not about what you eat, but how much and when. Eating large meals late at night or concentrating all your fibre into one meal often creates problems.

Finally, lifestyle still matters. Stress, poor sleep and relentless training load can undo even a good diet. Gut health improves fastest when nutrition and recovery habits work together.

The bigger picture

The biggest takeaway from these conversations is this.

Many everyday worries people live with are not fixed by more discipline or harder training. They are fixed by supporting the systems that keep the body resilient.

When gut health improves, sleep improves. When sleep improves, mood and recovery follow. When inflammation drops, performance becomes more consistent.

This is not about chasing optimisation. It is about removing friction and for many athletes and everyday people alike, the gut is the place to start.

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Thanks for being part of the tribe — I’m here to help you stay Battle Ready! ​ Simon