For many marathon runners, the greatest challenge isn't just the 26.2 miles ahead, but an urgent and often embarrassing need to find a toilet mid-race. This condition, colloquially known as runner's trots, runner's gut, or runner's stomach, affects a surprisingly high number of endurance athletes.
The Uncomfortable Reality of Long-Distance Running
Completing a marathon is a monumental physical feat, involving around 50,000 to 60,000 steps, burning over 3,000 calories, and losing multiple litres of sweat. While dangers like dehydration and heatstroke are well-known, gastrointestinal distress is a common but less discussed hazard. The condition is formally an overactive gastrointestinal tract triggered by the whole-body strain of running, leading to urgent, sometimes explosive diarrhoea.
This isn't a rare occurrence. Reports suggest that up to 96% of endurance runners experience some form of gut symptom during a race. The classic triad includes diarrhoea, cramping abdominal pain, and a heightened, uncontrollable urge to defecate. In most instances, it's manageable with fluid and electrolyte replenishment. However, in extreme cases, the presence of blood in faeces indicates potential mechanical damage to the bowel, possibly from the organ being jostled during the prolonged activity.
What Triggers Runner's Gut?
The exact cause is multifaceted, but experts have identified several key contributors. A primary factor is blood flow redistribution. When exercise begins, the body prioritises the heart, lungs, and muscles, diverting blood away from the digestive system. This reduced flow can irritate and inflame the gut lining and disrupt its bacterial colonies, which may explain why probiotics are being explored as a potential treatment.
Nutrition plays a critical role. Foods high in protein, fat, and fibre can increase gut activity and fermentation, which is why seasoned runners often opt for a simple, carbohydrate-rich breakfast before a race. Even performance aids can backfire: caffeine is a known stimulant with laxative effects for some individuals.
Certain carbohydrates can also be problematic. Lactose in dairy and high-fructose fruits like apples and pears can speed up gut transit, cause fluid retention, and lead to gas and diarrhoea. Furthermore, psychological factors like pre-race anxiety may exacerbate symptoms, given the well-established link between stress and irritable bowel syndrome.
Strategies for Prevention and Management
Preparation is paramount for avoiding an untimely toilet stop. Nutritional strategy is key. Runners should consume a familiar, energy-rich breakfast low in fibre, fat, and protein 2-3 hours before the start. Ideal options include a plain bagel, white toast, or a low-fibre cereal based on rice or corn. Fruits lower in fructose, such as bananas or berries, are safer choices. Crucially, test your race-day meal during training.
Hydration must be strategic. Drinking small, regular amounts of water or electrolyte-replenishing sports drinks helps maintain balance without overloading the bladder or gut. Avoid consuming large volumes in one go.
The best defence is understanding your own body. A training period spanning months, not weeks, allows athletes to identify triggers. Keeping a diary of food, symptoms, and training can reveal personal patterns. If symptoms strike during a race, slowing down, taking a brief break, and rehydrating can help. Remember, most marathon courses have toilets at frequent intervals for exactly this reason.
This insight comes from Dan Baumgardt, a Senior Lecturer at the University of Bristol's School of Physiology, Pharmacology and Neuroscience, highlighting the importance of physiological preparedness for the unique demands of marathon running.
