The present disclosure relates to a composition for preventing or treating metabolic diseases, in which the composition includes Bacteroides acidifaciens as an active ingredient. In addition, the present disclosure relates to a composition for oxidizing fat or inhibiting DPP-4, in which the composition includes Bacteroides acidifaciens as an active ingredient. In addition, the present disclosure relates to a transformant expressing a lean phenotype, in which an Atg7 gene is deleted in dendritic cells.
