Bariatric surgery is currently the most effective therapy for type 2 diabetes. However, the mechanisms underlying its beneficial effects remain elusive. Here we studied the effects of bariatric surgery on circulating meteorin-like (Metrnl) and oncostatin m (OSM) levels, two hormones intimately linked to energy homeostasis. Metrnl and OSM levels were assessed at baseline, 6 and 12 months after laparoscopic sleeve gastrectomy (LSG) in 25 patients with obesity, as well as in 33 normal-weight controls. At baseline, patients with obesity showed lower Metrnl and higher OSM levels compared to controls. LSG increased Metrnl and decreased OSM levels, in correlation to improvements in glucose and lipid homeostasis. Our data indicate that LSG conversely modulated Metrnl and OSM levels, and suggest that a dual approach modulating these two molecules might provide a novel strategy for obesity and type 2 diabetes treatment.