Peptide YY levels are decreased by fasting and elevated following caloric intake but are not regulated by leptin

Aims/hypothesis Peptide YY (PYY) is a gut-derived hormone that has been shown to reduce short-term food intake in animals and humans. It has been proposed that deficiency of PYY contributes to obesity in humans. However, the physiology of PYY regulation by factors such as caloric restriction, or by other molecules important in energy homeostasis, e.g. leptin, remains to be fully elucidated. Materials and methods We evaluated the effect on PYY levels of: (1) caloric ingestion (a mixed meal) in five healthy normal-weight subjects; (2) fasting for 2 or 3 days in eight lean men and seven lean women respectively; and (3) recombinant human leptin administration at physiological replacement and pharmacological doses. Results PYY levels increased 50% after a mixed meal (p=0.01), and short-term complete fasting for 2 or 3 days decreased leptin and PYY levels to 20-30% and 40-60% of baseline, respectively (both p