Endurance racing often triggers gastrointestinal distress through reduced blood flow to the gut during intense exercise, mechanical movement, and dietary factors. Consequences include nausea, cramping, vomiting, and voluntary withdrawal from a race, which can negate months of training and pose dehydration or electrolyte risks. Human and cultural factors such as habitual diets, travel to different food environments, and heat or humidity amplify susceptibility; for example, runners unaccustomed to high-carbohydrate feeds or to local cuisine may experience more symptoms.
Causes and physiological background
Key drivers are splanchnic hypoperfusion caused by blood flow redistribution during heavy exertion and osmotic load from concentrated sports nutrition. Use of nonsteroidal anti-inflammatory drugs increases mucosal vulnerability, and high-fiber or high-FODMAP pre-race meals can increase fermentable substrates and gas. Research by Ross J. Costa at Edith Cowan University emphasizes the multifactorial nature of these problems and the role of practical nutrition strategies to reduce symptoms.
Practical strategies shown to help
The strongest evidence supports practicing race nutrition in training, commonly called gut training, to increase tolerance to the volumes and concentrations of sports drinks and gels athletes will use on race day. Asker Jeukendrup at Liverpool John Moores University has advocated training the gut and progressively increasing carbohydrate intake during long workouts to improve absorption and reduce symptoms. Adopting multiple-transportable carbohydrates (combinations of glucose and fructose) can increase carbohydrate uptake without raising osmotic load, reducing the chance of bloating when compared with single-carbohydrate feeds.
Pre-race meal choices matter: choosing lower-FODMAP and lower-fiber meals in the 24 hours before competition often reduces fermentative symptoms, a practice supported in guidance by Louise Burke at the Australian Institute of Sport. Hydration strategies should avoid both underhydration and overly concentrated or excessive volumes; sipping tolerable amounts matched to sweat losses is preferable to aggressive fluid loading. Avoiding NSAIDs before races and testing caffeine or other stimulants in training are prudent because these agents can worsen GI upset in some athletes.
Implementing these strategies requires individualization and cultural sensitivity: athletes traveling to different climates or food systems should trial familiarized feeds during tapered long runs, and local culinary practices may require modification of pre-race meals. With structured experimentation under realistic training conditions, most runners can markedly reduce gastrointestinal problems and improve the likelihood of completing a marathon at their intended pace.