GHRL and obesity due to melanocortin 4 receptor deficiency: Mice lacking the gene for ghrelin or its receptor have normal food intake when fed chow, probably due to compensatory adaptation during embryonic development, but show a degree of protection from obesity when fed a high-fat diet, especially from an early age (Sun et al., 2003, 2004; Wortley et al., 2004, 2005).