GI Distress: Why Your Gut Betrays You on Long Runs
You know the feeling. Twelve kilometres in, everything is going well, and then your stomach turns. Cramp, nausea, the desperate scan for a toilet, or the gel you just took sitting like a brick. It is grim, it is common, and for a lot of women it is the thing that quietly ruins races.
Gut trouble is one of the most reported problems in endurance sport, and it hits runners hardest. It is also one of the most fixable, once you understand why it happens.
Here is what is going on in there, why women have a few extra variables to manage, and how to train your gut so it stops letting you down.
Your gut is trainable. A stomach that falls apart on long runs is not a life sentence, it is an untrained system being asked to do a job it has never practised.
Most GI distress comes down to three things happening at once: your gut gets jostled, it loses blood flow to your working muscles, and you feed it food it is not ready for. Fix those and the misery mostly disappears.
What is actually happening in there
When your gut goes wrong mid-session, it usually is not one villain. It is three, and they gang up.
1. The jostling
Running is a full-body shake. Every stride bounces your insides around, and that mechanical jarring irritates the gut directly. It is why runners get far more GI trouble than cyclists or swimmers, whose sports keep the core relatively still. If your stomach hates long runs but tolerates long rides, this is a big part of why. It also explains why downhill running, with its extra pounding, can be worse than flat ground, and why running tall with a braced core can take a little of the edge off.
2. The blood flow problem
This is the big one. When you work hard, your body sends blood to where it is needed, your muscles and your skin. To do that, it pulls blood away from your gut. The longer and harder you go, the less blood your digestive system gets.
A gut short on blood cannot do its job. Digestion slows, the gut lining gets stressed, and you feel it as nausea, cramp, bloating or an urgent need for a toilet. Heat and dehydration make it worse, because both pull even more blood away from the gut to help you cool down. Train hard in the heat, under-drink, and your gut is last in the queue for blood.
3. The fuelling mistakes
Then there is what you put in. A gut already jostled and starved of blood is in no state to handle a huge dose of concentrated sugar, a heavy pre-race meal full of fibre and fat, or a food it has never met before. Too much, too concentrated, too new, and it rebels.
The frustrating part is that you need to fuel to perform, especially over long distances. So the answer is never to stop eating. It is to teach your gut to cope with the fuel you need.
Two kinds of trouble
It helps to know which end of the system is complaining, because the fixes differ slightly.
Upper trouble is nausea, reflux, burping, a full or sloshing stomach, and in the worst cases vomiting. This often points to fuel and fluid sitting in the stomach and not clearing, so it tends to respond to less concentrated fuel, better hydration, and giving the stomach a job it has practised.
Lower trouble is cramping, wind, an urgent need for a toilet and loose stools. This is more about the gut lining under stress, food it cannot absorb fast enough, and things like fibre, certain sugars and anti-inflammatories. It tends to respond to gut training, lower-residue eating before big efforts, and cutting the hidden triggers.
Most women skew towards one end or the other. Work out which is yours and you can aim your fixes rather than throwing everything at the wall.
Your cycle is part of the picture
Here is where being a woman adds a couple of dials that most gut advice ignores completely.
Your hormones affect your gut directly. In the second half of your cycle, after ovulation, progesterone rises. Progesterone relaxes smooth muscle, and your gut is smooth muscle. That slows everything down, which is why many women feel more bloated, sluggish or constipated in the days before their period, then notice things loosen up dramatically once bleeding starts.
Oestrogen and progesterone also change how sensitive your gut is and how it handles water. The upshot is that the same long run, with the same fuelling, can feel completely different depending on where you are in your cycle. A session that sat fine one week leaves you doubled over two weeks later, and nothing about your training changed. Your internal chemistry did.
This is not a reason to feel cursed. It is useful information. If you track your symptoms against your cycle for a couple of months, patterns usually appear. Once you can see them, you can plan around them, choosing fuelling and even race-day expectations with your cycle phase in mind rather than being blindsided by it.
Women also report gut symptoms during exercise more often than men in a fair bit of the research. You are not imagining it, and you are not weak. You simply have more moving parts to manage, and managing them well is a genuine advantage.
The mistakes that wreck your gut
Before the fixes, the habits that keep people stuck. Most GI disasters trace back to at least one of these.
Training on an empty stomach or a sip of water, then slamming three gels and a sports drink on race day. Your gut has never rehearsed this. Of course it panics. The gut adapts to what you regularly ask of it, and asking nothing in training teaches it nothing.
Loading up on wholegrains, salad, beans and a fry-up two hours before a hard session. Fibre and fat sit heavy and slow to clear. They are great foods on a normal day and a liability right before you run.
A brand of gel from the goody bag, an unfamiliar sports drink at an aid station, a pre-race breakfast the hotel happened to serve. Race day is the worst possible time to introduce your gut to a stranger.
Turning up dehydrated and taking fuel that is too concentrated, so there is not enough fluid to move it through. Thick, sugary sludge with no water behind it is a recipe for cramps and a sprint to the bushes.
Your gut is a muscle system that adapts to load. Progress it the same way you progress your running:
- Start small. Take a little fuel on easy long sessions, even when you do not strictly need it.
- Build gradually. Nudge up the carbs per hour over weeks, letting your gut learn to absorb more.
- Rehearse the real thing. Practise your exact race fuel, in your race conditions, until it is boring.
A trained gut can comfortably handle far more fuel than an untrained one. That is a performance weapon, not just comfort.
What actually fixes it
These are the levers that turn a temperamental gut into a reliable one. None are quick hacks. All of them work when you do them consistently. Give them a full training block, not a single weekend, because the gut adapts the same way your legs do, gradually and in response to repeated, sensible demand.
A quick reassurance before the detail. You do not need to nail all four at once. Pick the one that matches your worst symptom, get it solid, then layer the next. Most women see a big improvement from just practising their fuel and sorting the day before, long before they fine-tune anything clever.
Regularly practise taking on carbohydrate during training, and slowly build the amount. Over a long race you may aim for somewhere around 60 to 90 grams of carbohydrate per hour, using a mix of glucose and fructose so your gut has more than one door to absorb it through. Work up to that number over weeks, never spring it on yourself.
In the 24 hours before a big effort, ease off very high-fibre, very fatty and very heavy foods. Some women do well lowering fermentable carbs, the so-called FODMAPs, for a day or two beforehand. Keep your pre-race meal familiar, lower in fibre and fat, and timed so it has cleared before you start.
Start well hydrated and keep drinking to a plan, especially in heat. Make sure your fuel has enough fluid with it to move through, rather than sitting as a thick sugary lump. Getting the balance of carbs to fluid right is often the difference between a happy gut and a grumpy one.
Two easy wins. Skip anti-inflammatories like ibuprofen around long sessions, because they stress the gut lining exactly when it is already under pressure. And if caffeine sends you running for a toilet, test your tolerance in training rather than gambling on it at a race.
Pop in your weight, race, target time and conditions, and get a clear plan for carbs, fluid and sodium per hour. The exact numbers to rehearse in training.
Build my fuelling planYour race-week gut plan
Put it together and race week gets simple. Here is the shape I give my athletes.
- All build cycle: practise your race fuel on long sessions until it is second nature.
- Two to three days out: ease back on very high-fibre and very fatty foods, keep meals familiar.
- Night before: a meal you have eaten before a hundred times, nothing adventurous.
- Race morning: your tried and tested breakfast, timed to clear, and start properly hydrated.
- During: your rehearsed carbs and fluid, on the schedule you have practised, no goody-bag experiments.
Boring is the goal. A gut that has done it all before in training has no reason to surprise you on the day. The confidence that comes from knowing your stomach will hold is worth as much as the fuel itself, because it frees you to race hard instead of running scared of the next aid station.
When it is more than exercise
One honest caveat. If your gut plays up outside of training too, if you have ongoing bloating, pain, changes in your bowels, or symptoms that do not fit the pattern above, that is worth getting checked properly. Exercise GI distress is one thing. Coeliac disease, IBS, IBD and other conditions are another, and they deserve a real diagnosis rather than a fuelling tweak. See your GP if something feels off beyond the long run.
For most women, though, this is a training problem with a training solution. Teach the gut, fuel it right, respect your cycle, and it stops being the thing that ends your good days early.
- ✓Your stomach turns on long runs or races no matter what you eat
- ✓You cannot seem to take on enough fuel without cramping or nausea
- ✓Your gut behaves differently depending on where you are in your cycle
- ✓You want a fuelling plan you can actually stomach, built and rehearsed properly
If that is you, this is very fixable. Let us build you a gut that behaves.
I coach endurance women to fuel properly and train their gut so it holds up when it matters. No more races ruined by your stomach.
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