FNDC5 and obesity disorder: To address these gaps, this study aimed (1) to examine the cross‐sectional associations of circulating irisin and adiponectin with obesity, sarcopenia and sarcopenic obesity in a population‐based cohort of middle‐aged and older Korean adults and (2) to assess how changes in these biomarkers over a 3‐year period are associated with these outcomes at follow‐up.