In human subjects, elevated circulating irisin levels are associated with a lower risk of insulin resistance in obese adults [24,25]; Choi et al. conducted experiments on the normal blood glucose and newly diagnosed T2DM subjects and found that serum irisin levels were decreased in T2DM patients, and the decreased level may be associated with the development of insulin resistance and T2DM, suggesting that irisin played an important role in the pathology of insulin resistance-related disorders [26]. Here, FNDC5 is linked to type 2 diabetes mellitus.