This study provides the most in-depth investigation of factors independently associated with serum GDF-15 concentrations in patients with, and without, T2DM who have NAFLD, and also demonstrates that older age, higher HbA1c, higher AST, higher hs-CRP, lower e-GFR and metformin use (but not gut microbiota composition, adipokines or measures of satiety) were all independently associated with higher serum GDF-15 concentrations. The gene discussed is GDF15; the disease is type 2 diabetes mellitus.