Antioxidant/Oxidant Balance as a novel approach to evaluate the effect on serum of long-term intake of plant antioxidant-rich foods

•For the first time Antioxidant/Oxidant Balance (AOB) is used in long-term studies.•AOB well shows improvement of serum antioxidant status due to antioxidant intake.•This occurs both if antioxidants come from a single food and from a diet.•Contrarily, measurements of Antioxidant Capacity (AC) of serum fails to do this.•AOB approach overcomes weaknesses of serum AC measurements reported in literature.