Fat-free body mass but not fat mass is associated with reduced gray matter volume of cortical brain regions implicated in autonomic and homeostatic regulation

► Associations of fat-free mass and fat mass with regional gray matter volume (GMV) ► Fat-free mass but not fat mass is associated with less prefrontal and insular GMV ► Associations of fat-free mass with less prefrontal GMV are independent of fat mass ► Fat-free mass affects regions involved in autonomic and homeostatic regulation ► Fat mass is not associated with GMV after adjustment for fat-free mass