Digestion and exercise: the 7 common mistakes you might be making

Runners during a road race, legs only, blurred

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Feeling heavy or bloated during your workouts? Perhaps you’ve been caught short mid-run and it’s made you hyper-aware of what you’re eating before you exercise. Whatever exercise-related gut issues you’ve faced, they can seriously hinder performance and make working out feel hard.

“Everyone’s gut reacts differently during exercise,” says Rob Hobson, a sports nutritionist with 15 years’ experience. “Some people can run for miles on a full stomach, while others feel queasy after just a banana. It depends on your body and, often, how anxious or relaxed you feel.”

During exercise, your body sends more blood to your muscles and skin to help with movement and temperature control. “This means there’s less blood going to your digestive system, slowing down digestion and causing bloating or nausea,” Rob explains.

You might also get a strong urge to race to the loo, as many runners have experienced.

To help reduce the chances of digestive mishaps, avoid these common mistakes…

A woman in gym gear with a breakfast bowl

MISTAKE #1: Eating too close to your workout

If you’ve gone for a jog or folded into a Downward Dog immediately after eating, you’ll be familiar with the discomfort of indigestion. If you’ve just had a main meal, it’s best to wait two to three hours before exercising, especially for endurance sports such as running.

“This allows time for digestion and glycogen (fuel) replenishment without discomfort,” says Rob. “Eat a meal that contains carbs, lean protein (such as chicken, tofu or fish) and minimal fat and fibre. Chicken with white rice and veg is a good shout.”

If you only have one to two hours until you exercise, tuck into a lighter snack of carbs and a small amount of protein. A smoothie with banana and protein powder or yogurt with fruit are good options here.

“In the final 30 to 60 minutes, stick with easily digested carbs only. This could be a banana or a rice cake with honey,” suggests Rob.

MISTAKE #2: Overdoing the fibre

As a nation, we don’t eat enough fibre. It’s the number-one nutrient for smooth digestion and comfortable number twos.

But, too much fibre before exercise, especially running, can also cause bloating, cramping and excess gas, according to Nichola Ludlam-Raine, registered dietitian and author of How Not To Eat Ultra-Processed. Fibre slows digestion and increases bulk in the gut. But, because blood has been diverted away from the gut as you exercise, these high-fibre foods could end up sitting in the gut for even longer, making you feel sluggish.

“Avoid large amounts of high-fibre cereals such as bran flakes, Weetabix and granola, especially those with dried fruit,” says Nichola. Give a miss to large amounts of wholemeal or seeded bread, beans, lentils or chickpeas and big portions of cruciferous veg such as broccoli or cabbage too.

“Aim for easily digestible carbohydrates with some protein: white sourdough toast or a bagel with nut butter and half a sliced banana is great,” recommends Nichola.

MISTAKE #3: Not drinking enough water

The general recommendation for adults is around 1.5 to 2 litres of fluid per day, but if you’re exercising and sweating, you will need more. Plus, water can help avoid any gut-related drama.

“Water helps break down food and moves waste through the gut. Even mild dehydration can slow digestion and lead to constipation or sluggishness,” warns Nichola.

To avoid a heavy, blocked-up feeling before a training session, Nichola recommends drinking some water 20 to 30 minutes before or after your pre-workout meal, to help food digest and ‘settle’.

Just avoid chugging large amounts of water right before exercise.

“A good rule of thumb is around 400-600ml of water two to three hours before exercise and a further 150-250ml 20 to 30 minutes before you begin,” says Nichola.

Person pouring water from a jug into a glass

MISTAKE #4: Loading up on sports drinks

They promise energy and faster recovery, but realistically you probably don’t need to keep downing brightly coloured sports drinks.

“Too much sugar, artificial sweeteners or acids, often found in sports drinks, can irritate the stomach, causing bloating and diarrhoea, especially if you’re not used to drinking them,” warns Nichola. To avoid tummy distress, choose drinks with around 4 to 8g of carbohydrates per 100ml.

Sensitive stomach? Leave 30 minutes between a sugary drink and intense exercise. “Check labels for sweeteners sorbitol or xylitol, which can cause gas or diarrhoea. It’s also best to sip rather than gulp, so you're not swallowing excess air,” adds Nichola.

“Water is usually fine, though you could consider an electrolyte drink during exercise instead, if it's over an hour. Some people suggest orange juice and a pinch of salt as a natural alternative too,” adds Nichola.

MISTAKE #5: Relying on gels

Energy gels might seem like the obvious quick fix for fuelling your workouts – they’re portable and high in quick-release carbs – but they can be a gut’s worst nightmare.

“Energy gels are concentrated sources of carbohydrates, usually glucose, fructose or maltodextrin, which draw water into the gut via osmosis,” explains Rob. This means that if you don’t drink enough water alongside them, or if the concentration is too high, these gels can pull fluid away from your bloodstream and into your intestines causing bloating or an urgent need for the loo.

“Some gels also contain caffeine, artificial sweeteners or sugar alcohols such as sorbitol, further irritating the gut,” says Rob. “If you’re sensitive, look for gels that use a 2:1 glucose-to-fructose ratio, which helps maximise absorption and reduce gut upset.”

For workouts beyond an hour, aim for 30-60g of carbohydrate per hour, roughly one gel every 20 to 30 minutes. Ideally, take your gels with around 200ml of water to help them digest a little easier.

There’s a whole world of ‘do this, don’t do that’ on social media, often from people who aren’t in any position to be handing out advice. But, no two guts or bodies are the same.

“Social media tends to oversimplify or generalise nutrition advice when, in reality, it should be highly individualised,” says Rob. Digestive tolerance is shaped by various factors such as genetics, how fit you are, what your diet usually looks like and even stress levels.

“Fuelling strategies should be tested and refined over time.”

It’s also worth remembering that many online influencers focus on aesthetics rather than performance, which is not how sports nutrition should be approached.

MISTAKE #7: Not training your gut

Big event coming up? Whether it’s a Hyrox competition, a parkrun or even a marathon, gut training is one of the best things you can do to prepare your body. “Just like your muscles, your gut can adapt,” says Nichola.

“Gut training involves gradually practising your nutrition strategy in the weeks leading up to an event, so your digestive system learns to tolerate the type and timing of food or drink you’ll use on the day.”

Start small, introducing small amounts of your pre-race meal or sports drink during training. Make sure you practise with the same foods and timing you’ll use for the event.

“Lower your intake of fat and fibre 24 to 48 hours before the big day if you’re prone to tummy troubles and make sure you stay hydrated,” adds Nichola.