Changes in metabolic risk factors and gut microbiota during weight gain in male first-year college athletes

Many contact sport athletes have high body mass index (BMI) and high metabolic disease risk. Rapid weight gain in first-year athletes may further increase this risk and affect gastrointestinal status. This study examined metabolic risk factor and gut microbiota during weight gain in 21 first-year male college athletes. We included members of student clubs for American football and rugby (ATH) and 10 controls without regular exercise habits (CON). Baseline measurements were taken within 3 months of joining the club, with follow-up after 6 months. B-mode ultrasound and blood and stool samples were analyzed. At the 6-month follow-up, the ATH group showed significant increases in body weight, weight-adjusted thicknesses of subcutaneous fat and abdominal cavity, and triglyceride levels, while gut microbiota diversity significantly decreased. No significant differences were observed in the CON group. The rate of change in body weight in the ATH group was significantly positively correlated with the change in triglyceride levels (r_s = 0.436, p < 0.05) and significantly negatively correlated with the change in Bacteroides abundance (r_s = -0.631, p < 0.05). In conclusion, weight gain after joining athletic clubs in first-year male college athletes was significantly associated with changes in blood lipid levels and gut microbiota.