Whitehead et al. Respond

Abstract

We agree that fruit and vegetable consumption is likely to confer health benefits by substituting refined carbohydrates, saturated fats, and other foodstuffs that are unambiguously deleterious to health. We argue, though, that fruit and vegetables convey additional active benefits to human health. While it is true that trials have consistently indicated that the impact of antioxidant supplement intake is null or negative, these studies highlight an overly reductionist approach. There exist important synergistic relationships between antioxidants1; therefore, high-dose supplementation of a circumscribed subset of phytochemicals is unlikely to be beneficial. Breakdown products of some antioxidants are themselves toxic,2 and because these antioxidants are readily expended by oxidizing agents when reserves of alternate endogenous antioxidants are low, administering high doses of single antioxidants could inadvertently precipitate oxidative tissue damage. As an example of the synergic relationships that exist, α-tocopherol oxidation toxicity is mitigated by carotenoids.3 Epidemiology is more clearly supportive of fruit and vegetable consumption being protective of chronic disease (particularly cardiovascular disease), even when controlling for dietary fat, total caloric intake, and other risk factors.4 Fruit and vegetables represent a particularly good (but by no means unique) source of a broad range of potentially beneficial nutrients including antioxidants, fiber, essential minerals, and other nonantioxidant phytochemicals.5 Fruit and vegetable consumption is likely to convey health benefits via multiple pathways, including the substitution of unhealthy foods, rather than via one of these mechanisms in isolation. Inuit people have coped with low fruit and vegetable consumption, but the historic impact of chronic disease in this population was relatively low because of short life expectancy precipitated by communicable illness and injury.6 Also, extant chronic disease risk in this population may have been mitigated by the intake of some antioxidant vitamins via a specialized diet comprising sea mammal liver and blubber.7 Adverse lifestyle factors are increasing susceptibility to chronic disease particularly in industrialized nations,8 meaning that the potentially protective effects of fruit and vegetable consumption will be increasingly important. Given the field of dietary epidemiology as a whole, we do not agree that fruit and vegetable consumption is appropriate or too high among those in the developed world. Studies in the United States consistently indicate that the adult diet comprises a low proportion of fruit and vegetables.9 Recent British surveys have also indicated that worryingly high numbers of individuals regularly consume no fruit and vegetables whatsoever.10 Consequently, it is clear that novel techniques to motivate long-term dietary improvement are urgently required.