Gastrointestinal complaints in runners are not due to small intestinal bacterial overgrowth

Seven long distance runners (5 female, mean age 29.1 years) with gastrointestinal complaints during and immediately after exercise without known gastrointestinal diseases performed Glucose hydrogen breath tests for detection of SIBO one week after a lactose hydrogen breath test checking for lactose intolerance. The most frequent symptoms were diarrhea (5/7, 71%) and flatulence (6/7, 86%). The study was conducted at a laboratory.In none of the subjects a pathological hydrogen production was observed after the intake of glucose. Only in one athlete a pathological hydrogen production was measured after the intake of lactose suggesting lactose intolerance.Gastrointestinal disorders in the examined long distance runners were not associated with small intestinal bacterial overgrowth.Gastrointestinal (GI) disturbances during or immediately after exercise are common among runners [1,2]. 20-50% of long distance runners are affected [3]. Both the upper and lower GI tract are involved. Symptoms are vomiting, nausea, bloating, heartburn and flatulence as well as watery and bloody diarrhea and anal incontinence [4]. The causative mechanisms are not completely understood. The mechanical irritation of the GI tract during running can change intestinal motility [5], additionally exercise causes a reduction of the mesenteric blood flow [6] and both may contribute to the symptoms. Both, a GI dysmotility as well as a reduced mesenteric blood flow are well known risk factors for development of small intestinal bacterial overgrowth (SIBO) [7,8]. Clinical manifestations of SIBO involve the upper and lower GI tract and are similar to the complaints of long distance runners. The gold standard in diagnosing SIBO consists in culture of jejunum aspirate for bacterial counts, but also non-invasive hydrogen breath testing with glucose (GHBT) is well established [9-12]. We hypothesized that due to the high weekly training volume with irritation of GI motility and repeated impairment of the mesent