Runner's diarrhea: What is it, what causes it, and how can it be prevented?

Purpose of review: Runner's diarrhea is an acute exercise-induced diarrhea. Usually, this is not a pathological situation but it can affect performance. This review focuses on the discussion of the main causes of runner's diarrhea and nutritional recommendations to prevent it. Recent findings: Although based on limited data, multiple transportable carbohydrate intake during exercise instead of glucose alone can be recommended for preventing the urge to defecate and (possibly) diarrhea. Additionally, avoiding ingestion of fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) is related to a lower incidence of reported gastrointestinal problems. There is, however, still no study that associates FODMAPs and runner's diarrhea. Gluten-free diets seem to have no impact on exercise-induced intestinal damage and there is no evidence to recommend this diet for the prevention of diarrhea in nonceliac athletes. Summary: The main causes of diarrhea in runners are ischemic, mechanical, and nutritional factors. For the prevention of diarrhea, it has been recommended that dehydration and the ingestion of fiber, fat, protein, high concentrated carbohydrate beverages, FODMAPs, caffeine, bicarbonate, and nonsteroidal anti-inflammatory drugs be avoided. However, the causes of diarrhea and nutritional strategies to prevent it are based on limited research and more studies are definitely needed.