Increasing gut short-chain fatty acids protects intestinal barrier function but does not spare muscle glycogen or impact aerobic performance.
Animal studies suggest gut microbiota-derived short-chain fatty acids (SCFA) provide an intestinal barrier-protecting, glycogen-sparing energy source that increases aerobic endurance performance, but confirmation in humans is needed. This study aimed to determine whether increasing colonic SCFA availability impacts intestinal barrier function, substrate metabolism, muscle glycogen and aerobic performance in healthy adults. Using a randomized, double-blind, crossover design 12 active men (age 18-30 years;40.0 ± 7.1 mL/kg/min) performed prescribed exercise and consumed a provided diet supplemented with acetylated and butyrylated high-amylose maize starch engineered to deliver SCFA to the colon (HAMS-A/B) or low-amylose maize starch (LAMS) for 7 days, separated by a 2 week washout. Indirect calorimetry, stable isotopes and blood, muscle and urine biomarkers were measured on intervention day 8 while participants completed 90 min of steady-state cycle ergometry (ExSS; 60 ± 5%) followed by a 5 km treadmill time trial. HAMS-A/B, relative to LAMS, increased faecal and serum SCFA. Multiple markers of intestinal barrier damage and permeability were lower, and the respiratory exchange ratio during ExSS was higher (0.02 [95% confidence interval (CI): 0.01, 0.03], Ptreatment < 0.001) following HAMS-A/B versus LAMS. However no between-treatment difference in glucose turnover, muscle glycogen depletion (14 µmol/kg/g dry wt. [95% CI: -116, 143], Pinteractio n = 0.613) or TT performance (5 s [95%CI: -44, 54], Ptreatment = 0.816) was observed. Increasing colonic and circulating SCFA modestly altered substrate oxidation and preserved intestinal barrier function during endurance exercise. However effects were not sufficient to spare muscle glycogen or increase aerobic endurance performance, leaving the practical relevance unclear and underscoring challenges inherent in translating promising preclinical findings to humans. KEY POINTS: Animal studies suggest gut microbiota-derived short-chain fatty acids (SCFA) provide an intestinal barrier-protecting, glycogen-sparing energy source that increases aerobic endurance performance, but confirmation in humans is lacking. A gut microbiota-targeted dietary supplementation strategy was used to deliver SCFA to the colon and successfully increased colonic and systemic SCFA concentrations in healthy, physically active adults before and during an endurance exercise bout and aerobic performance test. Increasing colonic and systemic SCFA availability preserved intestinal barrier function but did not impact glucose turnover, alter protein expression in muscle or spare muscle glycogen during endurance exercise. Increasing colonic and systemic SCFA availability did not impact aerobic endurance performance.