Effect of plant foods and beverages on plasma non-enzymatic antioxidant capacity in human subjects: a meta-analysis

Non-enzymatic antioxidant capacity (NEAC) represents a sensitive biomarker measuring the in vivo antioxidant potential of vegetable foods. To evaluate the effectiveness of plant-derived foods and beverages on the plasma non-enzymatic antioxidant system, we analysed all literature published upto May 2010. Data were extracted by two authors independently, and the effect size was summarised using standardised mean differences by a random-effects model. For the analysis, eighty-eight studies were included, reporting a total number of 122 interventions and involving 2890 subjects. There was overall evidence of the effectiveness of fruit, vegetables, dietary patterns based on plant foods, red wine and tea in increasing plasma NEAC. No changes were found for chocolate and fruit juices. We observed an overall effect size three times higher in subjects with risk factors when compared with healthy subjects. Total radical-trapping antioxidant parameter, oxygen radical absorbance capacity and ferric-reducing antioxidant power methods showed a similar increase in plasma NEAC following dietary supplementation, whereas Trolox equivalent antioxidant capacity did not respond to dietary supplementation. Data from the present meta-analysis show that plant-derived foods represent an effective strategy to enhance an endogenous antioxidant network in humans. This is particularly evident in the presence of oxidative stress-related risk factors.