Eat Your Veggies: They're Poisonous

In a recent post, the question came up whether it's "possible that many of the health effects of foods that have been attributed to antioxidants may actually be some other mechanism such as hormesis?" The answer to that is in the affirmative, since the putative antioxidant-containing foods, mainly fruits and vegetables, do not in fact contain much in the way of antioxidants, and in addition these compounds are rapidly cleared from the circulation, so actual physiologic concentrations of antioxidants are too low and too transient to do much of anything.

What about supplementing with antioxidants to get a larger dose? As it turns out, that might not be a good idea:

Conclusions Treatment with beta carotene, vitamin A, and vitamin E may increase mortality. The potential roles of vitamin C and selenium on mortality need further study.

A paper published in Free Radical Biology and Medicine asserts that something other than antioxidant capacity must be going on with flavonoids, which mainly come from fruits and vegetables:

Increased fruit and vegetable consumption is associated with a decreased incidence of cardiovascular diseases, cancer, and other chronic diseases. The beneficial health effects of fruits and vegetables have been attributed, in part, to antioxidant flavonoids present in these foods. Large, transient increases in the total antioxidant capacity of plasma have often been observed after the consumption of flavonoid-rich foods by humans. These observations led to the hypothesis that dietary flavonoids play a significant role as antioxidants in vivo, thereby reducing chronic disease risk. This notion, however, has been challenged recently by studies on the bioavailability of flavonoids, which indicate that they reach only very low concentrations in human plasma after the consumption of flavonoid-rich foods. In addition, most flavonoids are extensively metabolized in vivo, which can affect their antioxidant capacity. Furthermore, fruits and vegetables contain many macro- and micronutrients, in addition to flavonoids, that may directly or through their metabolism affect the total antioxidant capacity of plasma. In this article, we critically review the published research in this field with the goal to assess the contribution of dietary flavonoids to the total antioxidant capacity of plasma in humans. We conclude that the large increase in plasma total antioxidant capacity observed after the consumption of flavonoid-rich foods is not caused by the flavonoids themselves, but is likely the consequence of increased uric acid levels.

In all likelihood, the fact that "flavonoids are extensively metabolized" means that the body is trying to rid itself of them, i.e. they're poisonous.

The toxicological significance of exposures to synthetic chemicals is examined in the context of exposures to
naturally occurring chemicals. We calculate that 99.99% (by weight) of the pesticides in the American diet are chemicals that plants produce to defend themselves. Only 52 natural pesticides have been tested in high-dose animal cancer tests, and about half (27) are rodent carcinogens; these 27 are shown to be present in many common foods. We conclude that natural and synthetic chemicals are equally likely to be positive in animal cancer tests. We also conclude that at the low doses of most human exposures the comparative hazards of synthetic pesticide residues are insignificant.

So, it appears that when you eat fruits and vegetables, you're poisoning yourself, and that's a good thing.