FNDC5 and Obesity: Some studies have suggested that irisin ameliorates obesity, glucose disorders and insulin resistance14, 30, 31 and that circulating irisin is negatively associated with BMI and percentage of fat mass14, 32; however, other studies have found that irisin is positively correlated with these parameters33, 34 while others have revealed no correlation between irisin and BMI35, 36, 37.