Using MR–IVW analyses, we found that genetically predicted BMI was positively associated with HbA1c, fasting glucose and insulin (using the instrument unadjusted for BMI), T2DM liability, triglycerides, bioavailable testosterone, oestradiol among men, IL6, CRP, leptin and smoking, and inversely associated with IGF1, fasting glucose and insulin, and two-h glucose (2hGlu) (using instruments adjusted for BMI, likely due to collider bias), HDL-C, total cholesterol, total testosterone, sex hormone binding globulin (SHBG), 25(OH)D, adiponectin, PA and alcohol drinking. The gene discussed is LEP; the disease is type 2 diabetes mellitus.