Although they are recognized to be less obesity prone than mice on a BL/6 background, HFD feeding resulted in a modest but significant increase in adipose tissue mass in both T-bet−/− and WT BALB/c mice, but T-bet−/− mice were found to have greater fat mass compared with WT mice, independently of diet (Figure 1C). Here, TBXT is linked to obesity due to melanocortin 4 receptor deficiency.