Summary Recent evidence has disclosed a connection between gut microbial glycosidase activity and adiposity in obese. Here, we measured microbial α‐glucosidase and β‐galactosidase activities and sorted fluorescently labeled β‐galactosidase containing (βGAL) microorganisms in faecal samples of eight lean and thirteen obese adolescents that followed a controlled calorie restriction program during one year. β‐galactosidase is a h...