GHRL and obesity due to melanocortin 4 receptor deficiency: In humans, lean individuals homozygous for the obesity risk-associated fat mass and obesity-related (FTO) gene allele demonstrate attenuated postprandial reduction of circulating levels of acyl-ghrelin, as well as attenuated difference in BOLD responsiveness to high-calorie vs. low-calorie food images in homeostatic and hedonic brain regions in the fed vs. fasted state (Karra et al., 2013).