Train Your Gut For Marathon Running: Why It Could Make Or Break Your Race

Training for a marathon is about much more than building your fitness. While most runners carefully plan their long runs, speed sessions and recovery days, many overlook another important part of race preparation, training their gut. If you plan to use energy gels, sports drinks or other fuel during a marathon, your digestive system needs to be prepared just as much as your legs.

One of the most common reasons runners slow down or fail to reach their target time is stomach discomfort. Nausea, bloating, cramps and the sudden need to find a toilet can quickly turn months of training into a frustrating experience. Fortunately, many of these problems can be reduced by teaching your body to tolerate food and drink while running.

What Does Training Your Gut Mean?

Gut training simply means practising your race day nutrition during training. Just as your muscles adapt to longer distances and harder efforts, your digestive system can adapt to processing carbohydrates while you are running.

When you exercise, blood flow is redirected away from the digestive system towards your working muscles. This makes digestion more difficult and explains why foods or drinks that feel perfectly normal at home may suddenly cause problems during a marathon.

By regularly consuming carbohydrates during long runs, your stomach and intestines become better at absorbing fuel and delivering it to your muscles when you need it most.

Why Gut Training Matters

Your body stores enough carbohydrate to fuel roughly the first 90 minutes to two hours of running, depending on your pace and fitness. Beyond that point, your glycogen stores begin to fall and your body increasingly relies on the fuel you consume during the race.

If your digestive system struggles to absorb those carbohydrates, your energy levels can drop quickly. Many runners mistakenly believe they simply need to push through the fatigue, when in reality their body is struggling to process the fuel they have taken on.

A well trained gut allows you to absorb more carbohydrate comfortably, helping maintain your energy levels throughout the race and reducing the likelihood of hitting the wall.

Never Try Anything New On Race Day

Most experienced runners know the golden rule of marathon nutrition. Never try a new gel, sports drink or snack for the first time during a race.

Every product is slightly different. They vary in carbohydrate content, sweetness, thickness and the types of sugars they contain. Some include caffeine while others do not. Even small differences can affect how your stomach responds.

Your long training runs provide the perfect opportunity to discover which products work best for you and which ones you should avoid.

Practise Your Race Day Nutrition Strategy

Your gut training should closely mirror your race day nutrition plan. If you intend to take a gel every 30 to 40 minutes during your marathon, follow the same schedule during your longer training runs.

Use the same products, carry them in the same way and drink similar amounts of water alongside them. The more familiar everything feels before race day, the more confident you will be when the marathon arrives.

If your goal race provides a specific sports drink on the course, consider using that brand during training whenever possible. This reduces the chances of any unpleasant surprises on the day.

Read more about race day nutrition here.

Increase Your Carbohydrate Intake Gradually

Elite marathon runners often consume very high amounts of carbohydrate during races, sometimes exceeding 90 grams per hour. However, this level of intake is the result of extensive practice and is unnecessary for most recreational runners.

If you have never eaten while running before, begin with small amounts during your long runs. One gel every 45 to 60 minutes may be enough initially. As your body adapts, you can gradually increase the amount if your race strategy requires it.

There is no advantage in forcing large quantities of carbohydrates if your stomach cannot tolerate them comfortably.

Go easy on pasta

Choose Products That Suit You

There is no single perfect energy gel or sports drink. Some runners prefer thicker gels while others find more liquid options easier to digest. Some like chews or jelly sweets, while others prefer real food such as bananas or small pieces of flapjack during slower endurance events.

The important thing is to find products that you enjoy and that your digestive system handles well. Consistency is often more valuable than chasing the latest nutrition trend.

Once you have found something that works, avoid constantly changing brands. Different products contain different combinations of carbohydrates and ingredients, and frequent changes can make it harder to judge what suits you best.

Drink Enough But Not Too Much

Hydration and gut training work together. Taking an energy gel without enough water can leave it sitting in your stomach for longer than intended, increasing the chances of discomfort.

At the same time, drinking excessive amounts of water can dilute your body's sodium levels and leave you feeling bloated.

Practise drinking during your long runs so that you become comfortable carrying fluids or collecting drinks from aid stations. Your goal is to develop a routine that feels natural rather than something you have to think about during the marathon.

Read more about hydration here.

Expect Some Trial And Error

Few runners find their perfect nutrition strategy immediately. You may discover that one flavour works better than another, that caffeine agrees with you or that it causes stomach discomfort. Some runners find they need slightly more water, while others prefer to eat a little more frequently.

Keep notes after your longer runs. Record what you ate, when you ate it and how you felt afterwards. Over several weeks, patterns often begin to emerge that make it much easier to refine your race day plan.

Listen To Your Body

Some stomach discomfort during gut training is not unusual, particularly when you first begin practising with energy products. However, severe pain, vomiting or repeated digestive problems are not something you should simply ignore.

If certain products consistently cause problems, try alternatives rather than assuming all sports nutrition will have the same effect. Every runner's digestive system is different, and finding the right combination may take time.

Final Thoughts

Many runners spend months preparing their legs for race day but give very little thought to preparing their digestive system. Yet the ability to absorb fuel comfortably can make a significant difference during the final miles of a marathon, when fatigue begins to build and maintaining your energy becomes increasingly important.

By practising your race day nutrition throughout your training, introducing carbohydrates gradually and sticking with products that work well for you, you will arrive on the start line with greater confidence. Training your gut may never be the most exciting part of marathon preparation, but it could be one of the most valuable investments you make before race day.