A high fat diet and obesity increase adipocyte expression of the two main ALK7 ligands activin B and GDF-3 (Witthuhn and Bernlohr, 2001; Sjöholm et al., 2006; Hoggard et al., 2009), suggesting enhanced ALK7 signaling in obesity. Here, GDF3 is linked to obesity due to melanocortin 4 receptor deficiency.