In line with our previous findings showing no effect of vancomycin on host metabolism,13 a 14-day vancomycin treatment did not affect energy expenditure and substrate metabolism, glucose tolerance and insulin levels in adults with obesity and impaired glucose tolerance, although plasma SCFA and BA levels decreased.15 Furthermore, a 4-day treatment with an antibiotic cocktail including vancomycin did not affect postprandial glucose and insulin levels in healthy, normal weight men.16 Here, INS is linked to obesity due to melanocortin 4 receptor deficiency.