Obesity is reaching endemic state and has a major impact on health and economy. Weight loss interventions have limited efficacy on long term due to high prevalence of weight regain. Neuroendocrine factors play a role in weight regain as they regulate satiety, hunger and body weight. Neuroendocrine factors can be derived from the gut, e.g. ghrelin and peptide YY (PYY), from adipose tissue, e.g. leptin and adiponectin, or from the brain, e.g. neuropeptide Y (NPY) and α-melanotropin (α-MSH). These factors signal through various pathways to the brain, mainly to the hypothalamus. In patients with genetic or hypothalamic obesity, defects in these neuro-endocrine pathways lead to severe forms of obesity. We performed a review on available studies on neuroendocrine factors derived from the gut, adipose tissue and the brain in monogenetic obesity,  syndromic causes of obesity, such as Prader Willi Syndrome (PWS), and acquired causes of (hypothalamic) obesity in craniopharyngioma patients. In addition, we also summarize data on  neuroendocrine factors in conditions at the other site of the spectrum, i.e. in patients with undernutrition.

With the exception of PWS and anorexia nervosa, data on neuroendocrine factors in either obese or underweight patients is scarce. Leptin data are consistently related with the amount of fat mass, while for the other neuroendocrine factors results are varying.

This review might give direction for future research in both conditions of severe obesity and underweight.