Also, since we studied a sample of the general population in their usual living conditions, it was not impossible that some person would have exercised before the blood draw, and so increasing his or her irisin level; however, the fasting venous blood sample was drawn early in the morning and under fasting conditions, and our results are consistent with previous findings of the association of irisin with age, physical activity and insulin resistance, so the authors think that there is not bias. This evidence concerns the gene FNDC5 and Insulin resistance.