Research paper
Espelund U, Hansen TK, Højlund K, Beck-Nielsen H, Clausen JT, Hansen BS, Orskov H, Jørgensen JO, Frystyk J. Fasting unmasks a strong inverse association between ghrelin and cortisol in serum: studies in obese and normal-weight subjects. J Clin Endocrinol Metab. 2005 Feb;90(2):741-746. doi:10.1210/jc.2004-0604. Epub 2004 Nov 2. PMID: 15522942.
Why we cite it
Provides the strongest evidence for ghrelin's circadian rhythm during extended fasting — the 84-hour protocol with blood sampling every 3 hours is unusually rigorous. The headline finding is the powerful inverse ghrelin-cortisol correlation (r = -0.79), which means when cortisol peaks (morning stress response), ghrelin is suppressed, and when cortisol drops (afternoon), ghrelin rises. This connects hunger biology to stress biology. Also important: ghrelin did not stimulate GH during fasting, challenging the assumed ghrelin-GH link.