Described is the use of Eubacterium hallii et rel. and/or Alcaligenes faecalis et rel., as well as pharmaceutical, food, or feed compositions comprising these bacteria as a medicament, in particular, for preventing and/or treating insulin resistance and/or insulin resistance-related complications such as metabolic syndrome, dyslipidemia and type 2 diabetes mellitus, as well as insulin resistance in endocrine diseases (e.g., obese subjects with type 1 diabetes mellitus, Cushing's disease and lipodystrophy syndromes. Also described is a method for preventing and/or treating insulin resistance and/or insulin resistance-related complications such as dyslipidemia and type 2 diabetes mellitus as well as insulin resistance in endocrine diseases (e.g., obese subjects with type 1 diabetes mellitus, Cushing's disease and lipodystrophy syndromes) in a subject in need thereof, the method comprising the step of increasing the level of Eubacterium hallii et rel. and/or Alcaligenes faecalis et rel. in the small intestine.