FNDC5 and diabetes mellitus: Besides, researchers also found that irisin was positively correlated with BMI (P = 0.04), body fat percentage (P = 0.03), HbA1c (P = 0.03) [22], and fasting insulin (r = 0.303, P = 0.021) [24], yet negatively correlated with diabetes duration (r = 0.384, P = 0.002) [24]; partly similar observations were found in our study.