Quick Answer
The most common causes of stomach pain when running are eating too close to your run, reduced blood flow to the gut during exercise, poor breathing technique, dehydration, and the physical jolting of the digestive tract. Side stitches — sharp pains along the upper side of the abdomen — affect roughly 70% of runners at some point and are harmless. Most cases resolve with better pre-run nutrition timing, diaphragmatic breathing, and consistent hydration throughout the day.
The Main Types of Running Stomach Pain
Not all stomach pain during running has the same cause or the same fix. The table below maps the most common types to their likely cause and the first thing to try.
👉 Swipe to view full table
| Pain Type | Location | Most Likely Cause | First Fix |
|---|---|---|---|
| Side stitch | Upper side (left or right) | Peritoneum irritation, shallow breathing | Slow down, breathe deeply |
| Lower abdominal cramps | Lower abdomen | Eating too close to run, GI jostling | Adjust meal timing, pace |
| Nausea | General / upper stomach | Reduced gut blood flow, dehydration | Slow pace, sip water |
| Bloating / gas | General | High-fibre/fat pre-run food, swallowed air | Adjust pre-run food choices |
| Urgent bowel urge | Lower GI | Runner's gut / GI jostling | Pre-run toilet, nutrition review |
Causes of Stomach Pain When Running
1. Eating Too Close to Your Run
This is the most common and most avoidable cause. When you run, your body diverts blood flow away from the digestive system and towards your working muscles, heart, and lungs. If food is still being digested, that redirection causes a slowdown in gut motility — the movement of food through the digestive tract. The result is cramping, bloating, nausea, or that heavy, sloshing sensation in the stomach. The fuller your stomach, the worse the symptoms.
As a general rule, allow 2–3 hours after a main meal before running hard. A small, easily digestible snack — banana, white toast, rice cakes — can be consumed 45–60 minutes before a run without issue for most people. For detailed guidance on pre-run meal timing and what foods work best, see our guide on how long to wait after eating to run.
2. Side Stitches (ETAP)
A side stitch is a sharp, localised pain — usually in the upper right or left side of the abdomen — that appears during exercise. The medical term is exercise-related transient abdominal pain (ETAP). Research suggests it is most likely caused by irritation of the peritoneum, the membrane that lines the abdominal wall, which can occur due to the repetitive jolting of running, changes in breathing pattern, or increased pressure from a full stomach.
Side stitches are more common in less experienced runners and tend to reduce in frequency as fitness improves. They are not dangerous. To treat one mid-run: slow your pace, breathe deeply from the diaphragm (belly breathing rather than chest breathing), and try pressing your fingers gently into the site of the pain while exhaling. Most side stitches resolve within a few minutes of slowing down.
To prevent them: don’t eat a large meal in the 2–3 hours before running, avoid concentrated sugary drinks immediately before a run, and work on your breathing technique so it stays deep and rhythmic even at faster paces.
3. Reduced Blood Flow to the Gut
During moderate to high-intensity running, blood is redirected from the digestive organs to the muscles, heart, and lungs. This reduced gut perfusion temporarily impairs digestion and can cause cramping, nausea, or an urgent need to use the bathroom — especially in longer runs or races. The effect is more pronounced at higher intensities and in hot conditions, where blood is also diverted to the skin for cooling.
The practical fix is pacing. Running at a more controlled intensity — particularly in the early stages of a long run or race — reduces the degree of gut blood flow reduction and allows the digestive system to function more normally. Runners who go out too hard in the first few kilometres are far more likely to develop GI distress in the second half.
4. Physical Jostling of the Digestive Tract
Running is a high-impact, repetitive activity. Each foot strike sends a small shockwave through the body, and with it, the contents of the stomach and intestines. Over time — particularly on longer runs — this constant movement can irritate the gut lining, trigger peristalsis (the muscular contractions that move food through the digestive tract), and result in cramping, loose stools, or an urgent need for a bathroom stop.
This is partly why runner’s stomach is significantly more common in running than in cycling or swimming, where the body position and movement pattern produce less gut jostling. The main levers here are nutrition timing (reducing the amount of food in the gut when running), pacing, and gut training — gradually exposing the digestive system to the demands of running so it adapts over time.
5. Dehydration
Even mild dehydration affects how the gut functions. When fluid levels drop, digestion slows, and the risk of cramping, nausea, and general abdominal discomfort rises. Many runners arrive at training sessions already mildly dehydrated from daily life, then compound it by not drinking adequately during the run.
Consistent hydration throughout the day is more effective than trying to top up in the hour before a run. On runs over 45–60 minutes, sipping small amounts of fluid regularly prevents the cumulative dehydration that contributes to late-run GI distress. For practical guidance on carrying fluids and hydration strategies for longer runs, see our guide to how runners carry water and our endurance hydration strategy.
6. Poor Food Choices Before Running
Not all foods clear the digestive system at the same rate. High-fat and high-fibre foods take the longest to digest — often 4–6 hours or more — which means eating them too close to a run leaves them sitting in the gut during exercise. Spicy foods, dairy for those with sensitivity, and carbonated drinks are also common triggers. High-concentration carbohydrate drinks consumed immediately before a run can draw extra fluid into the gut and worsen cramping.
The foods that tend to work best close to a run are simple, easily digestible carbohydrates with low fat and fibre content: white toast, banana, rice cakes with honey, or a small bowl of oats. For a full breakdown of what to eat and when, see our pre-run nutrition guide.
7. Nerves and Race-Day Anxiety
The gut is highly sensitive to psychological stress. Anxiety activates the sympathetic nervous system, which speeds up gut motility and can trigger cramping, loose stools, or nausea — especially on race morning. This is why many runners experience GI symptoms on race day that they rarely experience in training, even when everything else is identical.
The most effective management is familiarity: practising your race-day nutrition routine in training so it feels normal by race day, building a consistent pre-race morning routine, and giving yourself enough time before the start to use the bathroom without rushing. Reducing caffeine intake on race morning can also help, as caffeine is a known gut stimulant.
How to Prevent Stomach Pain When Running: Summary
👉 Swipe to view full table
| Strategy | What to Do | Why It Helps |
|---|---|---|
| Time your meals | 2–3 hrs after main meal; 45–60 min after small snack | Reduces food in gut during blood flow diversion |
| Choose gut-friendly foods | Low fat, low fibre, easily digestible before runs | Faster gastric emptying, less gut loading |
| Stay hydrated daily | Consistent sipping throughout the day | Prevents dehydration-related cramping and nausea |
| Control your pace | Start conservatively, especially in first 5 km | Reduces intensity of gut blood flow diversion |
| Practise diaphragmatic breathing | Breathe from the belly, not the chest | Reduces peritoneum irritation, prevents stitches |
| Train your gut | Practise race-day nutrition in training runs | Gut adapts to absorbing fuel during exercise |
| Pre-race routine | Consistent morning routine, bathroom time, familiar foods | Reduces anxiety-related GI response |
Training Your Gut
One of the most underused strategies for managing running stomach pain is deliberate gut training. Just as your legs and cardiovascular system adapt to the demands of running over time, the digestive system can also be trained to tolerate fuelling and the physical demands of exercise more effectively.
Gut training involves regularly practising your intended race nutrition during long training runs — using the same gels, foods, or drinks you plan to use on race day, at the same intervals. This gradually teaches the gut to absorb carbohydrates during exercise without reacting. Runners who try new nutrition products for the first time on race day are far more likely to experience problems than those who have tested and repeated the same routine across multiple training sessions.
For longer runs and races, sipping fluids regularly rather than drinking large amounts infrequently also trains the gut to process fluid more efficiently during exercise. Even runners prone to GI distress often find that consistent gut training significantly reduces symptoms over a 6–12 week training block.
When Running Stomach Pain Needs Medical Attention
Most running-related stomach pain is functional — it has a clear cause and a clear fix. However, some symptoms warrant medical assessment. See a doctor if you experience severe or persistent pain that does not improve with pacing and nutrition changes, pain specifically localised to the lower right abdomen (which can indicate appendix or bowel issues), blood in the stool, unexplained weight loss alongside GI symptoms, or pain that regularly forces you to stop running entirely.
Runners with diagnosed conditions such as irritable bowel syndrome (IBS), coeliac disease, or Crohn’s disease may need to work with a sports dietitian to develop a running nutrition plan that minimises GI triggers specific to their condition.
Building a Running Plan That Works Around Your Gut
For most runners, solving stomach pain is a process of elimination — adjusting one variable at a time (meal timing, food choices, pacing, hydration) until the triggers are identified and managed. Keeping a simple training and nutrition log for a few weeks makes patterns much easier to spot: noting what you ate, when, and how your gut responded gives you data to work with rather than guesswork.
Structured training that includes a proper warm-up, builds intensity gradually, and avoids sudden spikes in mileage also reduces the frequency of GI symptoms. Runners who follow a progressive plan tend to experience fewer gut issues than those whose training is irregular, because the gut — like the legs — adapts best to consistent, progressive load. Our interval training guide and strength training program for runners cover how to structure sessions that build fitness without overloading the system.
Want a structured running plan that factors in nutrition and recovery?
Our coaches design training programmes around your goals, schedule, and individual needs — including guidance on fuelling for long runs and race day.
Get Running Coaching → View Running Plans →
FAQ: Stomach Pain When Running
Why do I get stomach pain when running?
The most common causes are eating too close to your run, reduced blood flow to the digestive system during exercise, physical jostling of the gut, poor breathing technique, and dehydration. Side stitches — sharp pains in the upper side of the abdomen — are the most frequent type and are generally harmless.
How do I stop stomach cramps when running?
Slow your pace, focus on deep diaphragmatic breathing, and press gently on the site of pain if it is a side stitch. Preventively, allow 2–3 hours after a main meal before running, avoid high-fat and high-fibre foods before runs, and stay consistently hydrated throughout the day.
What causes a side stitch when running?
A side stitch (ETAP) is most likely caused by irritation of the peritoneum — the membrane lining the abdominal wall. It is more common when the stomach is full, when breathing is shallow, and in less experienced runners. It is not dangerous and usually resolves quickly with reduced pace and controlled breathing.
How long should I wait after eating before running?
Allow 2–3 hours after a main meal before running. A small, easily digestible snack can be consumed 45–60 minutes before a run. High-fat, high-fibre, and spicy foods take longer to clear and are the most common dietary triggers for stomach pain during exercise.
When should I see a doctor about stomach pain while running?
See a doctor if the pain is severe, recurring, located in the lower right abdomen, accompanied by blood in the stool, or does not improve after addressing nutrition, hydration, and pacing. Persistent GI distress that doesn’t respond to the usual fixes may indicate an underlying digestive condition.
Find Your Next Running Race
Ready to put your training to the test? Here are some upcoming running events matched to this article.
