PharmacoNutrition Reviewed

Source: The Journal of Nutrition 137: 1493-1495
Article Type: Opinion
Author: H. Sies

Several times we discussed already the pros and cons of measuring “total antioxidant capacity” in food or biological fluids.
Today, I would like to somewhat conclude this issue by referring you to a recent article by Helmut Sies from Düsseldorf University, Germany. As there’s nothing to add, I would like to cite the article’s abstract as it is:

“In this contribution, I discuss the applicability of total antioxidant capacity (TAC) data obtained from plasma to human health issues and the use of TAC data for dietary items in epidemiological applications. Against the background of knowledge that major antioxidant defense is enzymatic, the use of the term “total” is not appropriate. Because dietary phytochemicals undergo uptake and metabolism, extrapolation to health effects requires direct molecular information, not a global parameter that uses an arbitrarily selected prooxidant source. Suitable alternatives are given in measuring functional biomarkers (surrogate endpoints). Although using TAC may be helpful in comparing different food items, the extrapolation to their contribution of antioxidant defense in vivo and, further, to health issues, should be discouraged, with the possible exception of the gastrointestinal tract. This is of particular importance because dietary phytochemicals and other small molecules have nonantioxidant activities. Direct assay of urate, ascorbate, and tocopherol, the major small-molecule contributors to TAC, is recommended.”

Image taken from: Crodausa

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.