Intervention study with a high or low antioxidant capacity diet: effects on circulating beta-carotene.

Abstract
BACKGROUND AND OBJECTIVES: A cross-sectional observation suggests that total antioxidant capacity (TAC) of the diet positively affects plasma concentrations of beta-carotene independent of beta-carotene intake. This study was carried out to investigate the effect of two dietary strategies, designed to be comparable in fruits, vegetables, fibre, alcohol and beta-carotene intake but substantially different in their TAC, on changes in antioxidant intake and antioxidant status, and in particular in circulating beta-carotene concentrations. SUBJECTS: A randomized cross-over intervention trial involving 33 healthy participants and consisting of two 14-day dietary periods (high TAC diet, HT; low TAC diet, LT) with a 14-day washout in between was conducted. RESULTS: Energy, macronutrient, dietary fibre, alcohol and beta-carotene intake was not significantly different between LT and HT, whereas intake of other carotenoids and dietary TAC was significantly higher in the HT than in the LT (P<0.001). Circulating carotenoids (with the exception of alpha-carotene, which followed an inverse trend) and alpha-tocopherol decreased significantly during the LT and increased during the HT period. Among these, beta-carotene almost doubled its concentration in plasma after the HT diet. CONCLUSIONS: The increase in circulating beta-carotene along with the increase in dietary TAC suggests that plasma beta-carotene could be a marker of TAC intake rather than of beta-carotene intake itself. This may explain, in part, why beta-carotene supplementation alone has shown no benefit in chronic disease prevention and adds to a putative beneficial role of high dietary TAC diets, which merits further investigation.