Irisin is a signaling protein that is released into the blood from skeletal muscle after proteolysis of the membrane protein FNDC5 . FNDC5, encoded by the Fndc5 gene. Irisin activity on subcutaneous white adipose tissue, both in culture and in vivo, stimulated UCP1 expression and induction of brown adipocytes in white adipose tissue depots, a process known as white fat ''browning''. Irisin increases total energy expenditure in animal models, and irisin expression in mice fed a high fat diet resulted in a significant improvement in glucose tolerance and a reduction in fasting insulin levels. Collectively, these data suggest that decreased serum irisin levels may be associated with the development of insulin resistance and Type 2 diabetes. Indeed, some studies showed that irisin levels were decreased in newly diagnosed Type 2 diabetes.