Plasma 5-HT and EC numbers in the proximal intestine are increased in rodent and human models of obesity, and in rodents this has been shown to occur ahead of weight gain [21,22,23,24], while genetic or pharmacological inhibition of TPH protects against diet-induced obesity and dysglycaemia in mouse models of obesity. The gene discussed is TPH1; the disease is obesity due to melanocortin 4 receptor deficiency.