Excessively high circulating PRL levels, as seen in patients with prolactinomas, are associated with metabolic dysfunction; moderately high PRL levels, defined as HomeoFIT-PRL [19], are protective against metabolic diseases in rodents and humans [20–22]; and low PRL levels correlate with a higher prevalence of metabolic diseases, including T2D and non-alcoholic fatty liver disease [19, 23, 24]. The gene discussed is PRL; the disease is type 2 diabetes mellitus.