FNDC5 and sarcopenia: The mechanisms regarding the association between sarcopenia and NAFLD are related to IR, chronic inflammation, oxidative stress, vitamin D deficiency, low physical activity, central obesity, and crosstalk with hepatokines (fibroblast growth factor 21, leukocyte cell-derived chemotaxin-2, and hepassocin) and myokines (irisin and myostatin) [27].