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. Here, GHRL is linked to polycystic ovary syndrome.