Source: European Journal of Clinical Nutrition (2007), 61: 69-76
Article Type: Original Contribution
Authors: S Valtuena, D del Rio, N Pellegrini, D Ardigo, L Franzini, S Salvatore, PM Piatti, P Riso, I Zavaroni, F Brighenti


Image taken from: http://www.healingwithnutrition.com/graphic/vitamins.gif

In my last post I pointed out the lack of disease-preventing efficiency antioxidants (e.g. polpyhenols, vtaminc C and E, carotenoids) show in many intervention studies.
In their recent paper, Valtuena et al. suggest that the total antioxidant capacity (TAC) of the diet acts as an independent predictor of plasma beta-carotene (a carotenoid) levels. They derive this conclusion from covariate analyses of their data showing a significant correlation between TAC of the diet and plasma beta-catotene levels. In contrast, the impact of oral beta-carotene intake on plasma levels was only of marginal significance, suggesting that plasma concentrations of beta-carotene are modulated by other determinants than its own intake. In summary, they conclude that a high TAC of the diet leads to enhanced plasma beta-carotene levels, possibly by preventing beta-carotene breakdown due to absorption of other antioxidants present in the diet. This in turn might also explain why high intake of fruits and vegetables not only lead to higher beta-carotene plasma concentrations but is also health beneficial, whereas supplementation with beta-carotene fails to reduce disease risk.

Aside from the TAC of the diet or food items, plasma or serum TAC is another parameter frequently reported in research papers.
The question now is whether the TAC of the diet (determined by the presence of antioxidants in the food) is linked to TAC of the plasma.
Here, I would like to draw your attention to a research article published in 2004 (Lotito et al.) showing that the consumption of apples (which are considered as antioxidant-rich food) indeed inceases plasma TAC. However, the changes in plasma TAC were due to effects of fructose (which is present in high amounts in apples, too) on plasma ureate (a major endogenous plasma antioxidant) levels (and not due to effects of ascorbate, i.e. vitamin C, present in the apples)
Taken together, those studying dietary effects on plasma TAC must rule out postprandial (and other confounding) effects on plasma TAC, prior directly linking the antioxidants present in the food under investigation to observed changes in plasma TAC.