In addition to its beneficial effect on obesity, irisin has also been linked to positive effects on many other diseases in which exercise is beneficial, including type 2 diabetes mellitus (T2DM) (16, 17), cardiovascular disease (CVD) (18), nonalcoholic fatty liver disease (NAFLD) (19), Alzheimer’s disease (20), and metabolic bone diseases (15). This evidence concerns the gene FNDC5 and type 2 diabetes mellitus.