Cells produce reactive oxygen species (ROS) as by-products of metabolism, which can give rise to a two-sided effect on the body under balanced and imbalanced oxidant homeostasis conditions. Antioxidant supplements exert their beneficial efficacy in the treatment of metabolic diseases only when the oxidant homeostasis is imbalanced with the over-production of ROS. Over-supplementation of antioxidant(s) can also cause an imbalanced oxidant homeostasis to exert detriments to the induction of metabolic diseases. This commentary raises a concern that prior to precise supplementation of antioxidants, an establishment of oxidant homeostasis status is required in avoiding an imbalanced oxidant homeostasis in vivo. In searching for valid oxidant stress makers, 3-Nitrotyrosine seems to fit in with the selection criteria and its quantification can be correlated with the degree of oxidative stress in vivo.