These recent studies of unchanged skeletal muscle and whole-body insulin sensitivity in Acc2-knockout mice contrast with earlier findings by Abu-Elheiga et al. (53), who reported that ACC2 deletion leads to increased fat oxidation, reduced body weight and protection against diet-induced obesity and IR (54, 55, 56). The gene discussed is ACACB; the disease is obesity due to melanocortin 4 receptor deficiency.