Short‐term high‐intensity interval training exercise does not affect gut bacterial community diversity or composition of lean and overweight men

New Findings What is the central question of this study? Does short‐term high‐intensity interval training alter the composition of the microbiome and is this associated with exercise‐induced improvements in cardiorespiratory fitness and insulin sensitivity? What is the main finding and its importance? Although high‐intensity interval training increased insulin sensitivity and cardiovascular fitness, it did not alter the composition of the microbiome. This suggests that changes in the composition of the microbiome that occur with prolonged exercise training might be in response to changes in metabolic health rather than driving exercise training‐induced adaptations. Regular exercise reduces the risk of metabolic diseases, and the composition of the gut microbiome has been associated with metabolic function. We investigated whether short‐term high‐intensity interval training (HIIT) altered the diversity and composition of the bacterial community and whether there were associations with markers of insulin sensitivity or aerobic fitness. Cardiorespiratory fitness (V̇O2peak) and body composition (dual energy X‐ray absorptiometry scan) were assessed and faecal and fasted blood samples collected from 14 lean (fat mass 21 ± 2%, aged 29 ± 2 years) and 15 overweight (fat mass 33 ± 2%, aged 31 ± 2 years) men before and after 3 weeks of HIIT training (8–12 × 60 s cycle ergometer bouts at V̇O2peak power output interspersed by 75 s rest, three times per week). Gut microbiome composition was analysed by 16S rRNA gene amplicon sequencing. The HIIT significantly increased the aerobic fitness of both groups (P