PYY and polycystic ovary syndrome: Furthermore, the mediators of the gut-brain axis—such as ghrelin, serotonin, and PYY—play a role in appetite regulation and psychological wellbeing in women with PCOS (Saydam and Yildiz, 2016) and their levels were found to increase after treatment, with Ghrelin and PYY negatively correlated with Escherichia-Shigella (Liu et al., 2017).