DAVID E STEVENSON
The New Zealand Institute for Plant and Food Research Limited
Plant & Food Research Ruakura, Private Bag 3230, Waikato Mail Centre, Hamilton, 3240, New Zealand

Abstract

It is popularly believed that antioxidants protect us from “harmful reactive oxygen species” by neutralising them before they can damage our cells or DNA. There is, however, no conclusive evidence of a strong link between dietary antioxidants and beneficial effects on human health. This lack of evidence may have arisen from a lack of clarity of how polyphenols work. Polyphenols appear to assist the body to control, or manage, potentially–damaging oxidative stress. Our new understanding of this “indirect” antioxidant action and its scientific basis are briefly reviewed. The implications for human health and functional food development are covered in Part 2.

ABBREVIATIONS

ROS: Reactive oxygen species, i.e., free radicals, or compounds that easily form them. ETC: Electron transport chain; a group of mitochondrial proteins that generates ATP (adenosine triphosphate). MnSOD: Mitochondrial form of the antioxidant enzyme, superoxide dismutase. MB: Mitochondrial biogenesis; the increase of mitochondrial numbers within cells.

INTRODUCTION
Many consumers are convinced that eating fruits and vegetables helps keep them healthy and that polyphenolic antioxidants are mainly responsible for the health benefits (1). Consequently, many fruits and high-polyphenol functional foods have been marketed on the basis of high antioxidant content with the idea that excessive production of damaging free radicals, or weakening of the body’s defences against them, also termed, “oxidative stress’ can be neutralised by a sufficiently high intake of antioxidants.
Contrary to popular beliefs, however, the European Food Safety Authority (EFSA) does not support antioxidant health claims (other than a few for vitamin C) on the grounds that there is no scientific basis for a link between antioxid ...