PYY and polycystic ovary syndrome: Compared with controls, PCOS patients have significant decreases in the serotonin, ghrelin, and PYY levels, indicating that the mediators of the brain-gut axis are associated with PCOS.149 A recent study showed that compared with that of BMI-matched normal adolescents, the gut microbiome of obese adolescents with PCOS is altered and that these alterations include decreased alpha diversity, which is strongly associated with higher testosterone concentrations.150