The impact of a 48-h high-carbohydrate low-fermentable oligo-, di-, monosaccharide and polyol diet in athletes with concurrent exercise-associated gastrointestinal symptoms and detected small intestinal bacterial overgrowth

Small intestinal bacterial overgrowth (SIBO) is a condition characterised by an increased concentration of bacteria in the small intestine, leading to fermentation and subsequent gas production. SIBO symptoms are similar to those reported by athletes who experience exercise-associated gastrointestinal symptoms (Ex-GIS), including abdominal bloating and pain, and abnormal defecation (1). A low fermentable oligo-, di-, monosaccharide and polyol (FODMAP) diet has previously been shown to reduce the incidence and severity of Ex-GIS (1). This case-series explored the efficacy of a low-FODMAP diet in trained athletes with SIBO who become symptomatic during exercise. Three recreational to elite-level athletes who were retrospectively diagnosed with SIBO, and experienced severe recurrent Ex-GIS, volunteered to participate. Athletes were encouraged to implement their typical nutrition and hydration strategies 48-h before and during a gastrointestinal assessment during exercise (GastroAxEx). During the GastroAxEx, athletes ran on a motorised treadmill (average ± SD, 9.2 ± 2.7 km/h) for 3-h in temperate ambient conditions (19.7 ± 0.8°C, 64 ± 10% RH), with physiological strain and Ex-GIS outcomes measured. To determine orocaecal transit time, athletes consumed a 150 mL solution containing 20 g of lactulose 30 min into the final hour of exercise. Breath samples were collected at baseline and every 15 minutes during recovery to measure breath hydrogen (H2) and methane (CH4). Following the GastroAxEx, individualised therapeutic intervention and management strategies based on collected data and best-practice guidelines were recommended, including the implementation of a 48-h high-carbohydrate low-FODMAP (HC-LFOD) diet before endurance exercise sessions (>3-h). Follow-ups were conducted to facilitate compliance. This enabled anecdotal feedback on the efficacy of the strategies. During the GastroAxEx, athletes consumed approximately 450 mL/h (range: 242-693 mL/h) of fluid and 43 g/h (12-100 g/h) of carbohydrate, resulting in a 1.8% (1.6-2.4%) body mass loss. Loose stools were the predominant severe symptom (rated 10/10) experienced before (n=1), during (n=3/3) and the recovery period after exercise (n=3/3). Baseline breath H2 and CH4 concentrations were 24 ppm (3-45 ppm) and 34 ppm (13-74 ppm), respectively. Orocaecal transit time was normal (45-60 min) for all athletes. All athletes successfully implemented a 48-h HC-LFOD diet [(carbohydrate 9.2 g/kg/d (8.6-9.8 g/kg/d) FODMAP 3.5 g/d (2.6-5.1 g/d)] before a prolonged endurance event. In response to a 48-h HC-LFOD diet, athletes reported improved performance and reduced incidence and severity of Ex-GIS, including total gut discomfort, total-GIS, upper- and lower-GIS, nausea, dizziness and stitch, during an endurance event. No athletes experienced loose stools. The most severe symptom reported was belching (5/10), experienced by one athlete. Athletes with SIBO who implemented a 48-h HC-LFOD diet reported reduced incidence and severity of Ex-GIS, which may have favourable performance implications, warranting further investigation.