Diarrhea. It’s bad enough trying to spell it, never mind trying to cope with it while running. If you’ve ever had the unfortunate experience of getting rather too close to nature while frantically searching for a discrete bush on the trails, or having a race ruined by stomach cramps, we’re here to help. Nutrition expert Renee McGregor spoke to us about finding the cause of runner’s belly, how to stop it from arising during a jog, and how to combat a dicky tummy mid-race, so we can all stick to the right kind of runs.
Why do people get runner’s belly?
A range of specific factors are outlined in the sections below, but most obviously, says McGregor, the problem is the movement involved in running. All that bouncing motion is a major factor in causing the gut to become loose.
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Running too soon after eating
Going out running with too much food on board can put too much strain on your body’s systems, as it’s now being asked to move as well as digest, McGregor explains. ‘Remember that, when we run, all the blood flow is directed away from the stomach and into our muscles to help us move,’ she says. ‘That means that there’s no blood flow in the stomach to allow for digestion to occur. So if you’ve got a full tummy, that could be another reason why you end up with the trots.’
Running without enough fuel
On the other hand, running on an empty stomach can also be problematic. It may sound counter-intuitive, but here’s why: ‘If you’re not consuming enough energy before you run, and maybe you’re just slightly chronically under-fuelled, that can actually lead to what we call gut permeability – something that is known as ‘leaky gut’ – where you tend to quite regularly get an upset stomach. So a lot of people will not eat before a run because they’ve associated runner’s trots with eating when, actually, it’s probably one of the worst things you can do.’
Dehydration
Dehydration is a major factor in diarrhea for runners. Some people don’t drink sufficiently before they head out running, and others don’t take on enough water during their longer runs or races, especially on warm days. ‘When it comes to racing, people tend to blame energy gels. But, actually, that’s very unlikely – especially during endurance runs. So when you’re doing marathons or ultramarathons and if it’s also hot, people don’t tend to hydrate properly.’
When racing at a faster pace than you’re used to, perhaps when going for a PB, it’s tempting to make any water stops as brief as possible. This makes it easy to neglect the amount of fluid you really need to perform well. ‘They just grab a drink and have a couple of sips and it’s quite difficult to swallow enough,’ says McGregor. ‘So over the course of marathon, they’ll have only had, say, 400-500ml, but if you’ve been out there for three or four hours, it’s not really enough.’
What happens then, explains McGregor, is that any energy taken on board (like energy gels, for example) tends to concentrate in the stomach. ‘And if it’s too concentrated in our stomach, it’s going to want to come out,’ she says.
Don’t forget that dehydration isn’t only caused by not drinking enough. When you sweat you’re also losing electrolytes, which are vital to the process too. ‘People tend to make the mistake of drinking water but not realising they’re losing salt at the same time – you need the salt to draw the water back in.’
Jitters before a race
It can feel like race organisers always want us to arrive at their events way too early – until you see the queue for the toilets. Natural worries about the challenge ahead can also have an affect on your digestive system. ‘Basically, you’re in fight or flight, your adrenaline is high and a lot goes on when you’re in that phase of vigilance,’ notes McGregor. ‘Your heart rate goes up, your adrenaline is up and your bowels go – and that’s completely normal. So, anxiety and stress is absolutely more likely to cause you to go the toilet more often than you normally would.’
Time of the month
Best Garmin deals menstrual cycle. ‘Females who have natural menstrual cycles – so those not on the pill – might experience more stomach issues during their luteal phase, which is the pre-menstrual phase. At this stage in your cycle, it’s worth being mindful of the amount of fibre you’re eating because it’s likely to cause more problems than it would in the middle of your cycle.’
Racing too hard
If you’re racing seriously, especially in a longer challenge such as a marathon, the mix of extreme exertion and a high possibility of dehydration could well cause problems downstairs.
‘The thing with marathons is that people end up going out way too hard with excitement – because for the first half of a marathon, you feel great. But if you push a bit extra – even if it’s just 10 seconds or 15 seconds more per mile – you’re using up your energy stores very quickly, so you’re going to Reasons why your feet can go numb while you run quicker. But also, if you’re working hard, both your heart rate and your core temperature goes up, so you’ll be sweating more and losing a bit more salt – and then not replacing that fluid. And again, if you try to put something concentrated into your gut, like an energy gel, that can result in stomach issues – including vomiting – because your salt balance is off.’
What can runners do to prevent diarrhea?
Stay hydrated
Staying in control of your hydration is key here. If you have enough water on board, the contents of your stomach are less likely to become concentrated and cause discomfort. There’s no magic number for how much water to drink per hour – advice can vary between 300 and 800ml – so bear in mind that your specific needs will vary depending on the air temperature and how much you tend to sweat, not just how thirsty you feel.
Don’t forget about electrolytes
As well as remembering to drink enough water, it’s vital to replace the sodium you lose when you sweat. That’s needed to help water to be absorbed by your body. ‘While sports companies promote gels, they often don’t contain huge amounts of electrolytes, so people think they’re getting what they need with a gel when they’re not,’ says McGregor.
For distances over a half marathon, McGregor recommends taking on electrolytes mid-run. ‘Once you get into the realm of the marathon, people will usually be running for over three hours, which means you’ll be sweating for over three hours. So, you’re going to need to replace those electrolytes.’ McGregor suggests using salt tablets, electrolytes, energy drinks and even food if you can stomach it (like salted peanuts and cured meat).
Try eating and drinking a little before you run
It doesn’t necessarily take serious planning to fuel yourself adequately before you head out. McGregor proposes just a little bit to eat and drink as you get going. ‘If you’re constantly getting an upset stomach, try having a glass of water and a banana before you head out,’ she suggests. ‘A lot of people think they need to have their breakfast before they go, but you don’t need to have your whole breakfast. For example, when I go for a run in the morning, I might have a piece of toast half an hour to 45 minutes before I go, so I’ve had something. It’s not heavy – but I’ve had something and that tends to help.’
Slow down with the gels
Weekend workouts can still help your heart health energy gel goes down in one hit, such is the amount of glucose arriving in the stomach. McGregor suggests it’s better to get them down more gradually. ‘Taking a gel over the course of, say, four or five minutes is much better than trying to take a gel all in one go, which the body can’t cope while it’s trying to run at the same time.’
Fuel correctly when training as well as racing
Believe it or not, training runs count as times when nutrition is required too. If you try an unfamiliar gel for the first time on race day, you’re asking for trouble. ‘The biggest mistake I see is with people who won’t train with the products they’re going to use on race day. Then, on race day, they start using them and think they’re going to be fine when they don’t know if the body is going to tolerate it or not. There will be some products that your body doesn’t like very much and you do have to work that out before you go out.’
That’s why it’s so important to not take unfamiliar products off the course. ‘Sometimes, people don’t want to carry the gels they’ve practised with, so they take the gels the marathon is giving out because this think a gel is a gel, which is a mistake.’
Always take notes
McGregor recommends that runners – particularly female runners – keep a diary of when they’re noticing stomach issues. ‘Female runners might find a pattern in their cycle, which is something you can work around,’ she says. ‘But it’s thinking about other things like when you had your last meal, or whether you had a lot of more fibre on a particular day that led to issues one or two days later. It’s not always the last meal immediately before a run that causes problems – it can be one you had 12, 24 or even 36 hours before.’
Although we do need fibre in our diet, excess fibre can cause us to be a little more mobile in the gut region. ‘It’s just about being aware that things like lentils, beans and pulses can take a bit longer to digest, hence why they are good for you – so it’s just being mindful and seeing if you can see patterns.’
She also recommends looking at your dairy intake. ‘While it’s very rare, some people do find that having dairy, particularly in the run up to a race, can mean that they’re more likely to end up with stomach problems. But, it is quite rare.’
It’s about finding out what might be the cause for you because everyone is different. If you’ve tried everything and are still struggling, McGregor suggests taking a probiotic supplement. ‘That tends to help a lot of people if they’re really stuck. Our gut biomes are so affected by stress, lifestyle, exercise and so on, that sometimes, if you have a little bit of disequilibrium in the gut – if you’ve got a bit of dysbiosis going on – taking a probiotic can help to sort that out and encourage good bacteria to colonise and allow equilibrium back in the gut again.’
What to do about runner’s belly during a race
If you find yourself with runner’s trots during a race, try not to panic. Slow down your pace and take on some fluids and electrolytes, if you know you’ve not taken on enough by that point. ‘Slow things down, have a few sips of water, take a salt capsule and see if that makes a difference,’ advises McGregor.
What causes diarrhea during or after a run Runner’s World, overseeing RW’s new membership programme, set to launch later this year. She has been with the brand for close to three years now – previously working as deputy digital editor, where she covered all manner of running topics, spanning training, health, injury, nutrition and gear. Over the years, she’s interviewed an abundance of awe-inspiring athletes, from top-tier ultrarunners and Olympic champions to everyday runners who have accomplished extraordinary things. Jen has been a sports journalist for 10 years; she is the former editor of Women’s Running magazine and has also worked as Sports Editor at Red Bull. She started running a decade ago and likes to dabble in triathlon a little, too. You’ll find she’s happiest plodding down the Thames path or chowing down on a post-run pastry.
