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
A study of ghrelin’s circadian rhythm during fasting, with blood sampled every 3 hours from 12 to 84 hours of fasting in 33 young adults. The rhythm persisted throughout. The headline finding is a strong inverse temporal association between ghrelin and cortisol (r = −0.79), which the authors call ”a novel finding”, hedged: ”ghrelin appears to be related to cortisol. However, further studies are needed to elucidate the physiological mechanisms behind this relationship.” For the project, it links hunger biology to stress biology. The study found ”no evidence that ghrelin stimulates GH release during fasting”. (Corrected 2026-09-19. This read ”the strongest evidence” and ”unusually rigorous”, both rankings; ”which means when cortisol peaks … ghrelin is suppressed”, a mechanism read into a correlation the authors leave unexplained; and ”challenging the assumed ghrelin-GH link”, where the authors report only an absence of evidence.)