23 September 2003

by Georgina Hall
Crop & Food Research

Scientists, by training and usually temperament, are careful and considered people. Crop & Food Research’s Dr. Carolyn Lister is no different, but she doesn’t mince her words on the importance to human health of the antioxidants found mainly in fruits, vegetables and grain.

“The greatest revolution in medicine since the discovery of vaccination was the discovery of vitamins and how they prevented deficiency diseases like scurvy, pellagra and beri-beri.

“Like many medical researchers I think that antioxidants are the key to a second revolution in dietary science,” she says.

Vegetables, fruits and other plant-based foods must play a central role in this. There are few or no antioxidants in most animal-derived foods such as meat or milk and popping a supplement pill is not the answer, she says. This is because antioxidants work in a number of different ways and most supplements do not provide the same diversity of antioxidants available in fruits and vegetables. Also antioxidant levels may vary - excessive amounts of particular compounds in some supplements may be harmful or induce a shortage of another antioxidant. “It’s difficult to pack a plateful of vegetables into a single capsule,” she says.

To spread the word on this and the other latest antioxidant science, she has recently written a book “Antioxidants: a health revolution”.

It spells out that the healthiest approach is to eat five – and preferably eight or more – servings of colourful fruits and vegetables per day. Wholegrain cereals, herbs, tea, fruit juice and red wine (in moderation!) will help.

Although research internationally is still moving quickly and some ‘ifs’, ‘buts’ and ‘maybes’ surround antioxidants, Dr Lister says these points are clear: antioxidants really are good for health; the best sources are fruit, vegetables and grain; and strong colour is a good guide to antioxidant content.

In fact it was colour, that first led Dr Lister into the antioxidants field. She was researching colour in squash and apples before winning a Crop & Food Research Fellowship on the health benefits of red wine at the University of Glasgow. On her return to New Zealand in 1998 she started, with funding from the Foundation for Research, Science and Technology (FRST), on the plant-based foods programme focusing on antioxidants.

Dr Lister is now also part of ‘Vital Vegetables’, the major trans-Tasman research programme to enhance the health benefits of vegetables. Partners in the project are VegFed and Ausveg, together with Crop & Food Research and Australia’s Department of Primary Industry (Victoria) with support from FRST and Horticulture Australia Ltd. Her antioxidant book is the programme’s first output.

Other research links include those to a Christchurch School of Medicine project on free radicals and their role in disease which in turn provides additional data for Crop & Food Research’s Food Composition Database. As well, Dr Lister works with the institute’s plant breeders understanding how cultivar and growing conditions may effect the composition of particular crops. Industry has helped fund projects on potatoes, asparagus and berryfruit.

Dr Lister says that while some old wives tales, such as ‘an apple a day keeps the doctor away’ has an element of truth – but probably only if you eat the skin - not all the myths about fruits and vegetables are right.

Raw vegetables are not, for example, always better than cooked or processed. Pumpkins, carrots and tomatoes contain carotenoids, which are actually more easily absorbed by the body if these vegetables are cooked. Steaming is preferable to boiling as this prevents leaching of water-soluble antioxidants into the cooking water.

She recommends not peeling potatoes, apples or other fruits or vegetables unnecessarily and steaming vegetables, rather than boiling or microwaving, to retain more antioxidants.

But her final word of caution is not to go overboard: “small dietary changes can often make a big difference. Balance is the answer.”

“Antioxidants: a health revolution” (recommended retail price $19.95)
is available in all major bookshops. It can also be ordered from Damien Coup at Crop & Food Research phone (03) 325-6400 or email: coupd@crop.cri.nz or fax: (03) 325 2074


ANNEX 1

Antioxidants are substances that de-activate free radicals and oxidants, rendering them harmless. By counteracting these ‘poisons’, antioxidants make for better health and slow down the degeneration associated with ageing.

Some contact with free radicals and oxidants is inevitable as they are produced by normal processes in the body as well as from food and other environmental sources. The modern diet, with its reliance on fried or refined foods and preservatives, increases the burden of harmful compounds. Even ultra-violet light on the skin is harmful, not to mention smoking, one of the worst sources of oxidants, whether deliberate or passive.

In general, our antioxidant needs are increasing because as we live longer, the results of damage to body tissues become more apparent.

There are many kinds of antioxidants and antioxidant defence mechanisms, some of which are produced in the body, while others like Vitamin C are derived from food. Some antioxidants act directly scavenging the damaging free radicals, while others act indirectly boosting the body’s defence mechanisms or repairing damage.

Common dietary antioxidants include:

Vitamin C: especially high in blackcurrants, broccoli and capsicums, citrus fruit, kiwifruit and watercress.

Vitamin E: from dark leafy greens, avocados, cold-pressed oil.

Carotenoids: the compounds that make carrots orange, tomatoes red and squash yellow. Also in broccoli and silverbeet and other yellow, orange and green fruit and vegetables.

Flavonoids and other phenolics: found in all plants to some degree. Some phenolics give the blue, red and purple colours to fruit and vegetables. High levels in apple skins, asparagus, blackcurrants and other berryfruit, herbs, onions, soybeans and tea.

Selenium: really an essential element rather than an antioxidant but it is essential to enzymes involved in the body’s natural antioxidant defences.
Found in organ meats, seafood and grains but levels can be low in produce because New Zealand’s soils are deficient.

ANNEX 2

Some top sources of antioxidants in alphabetical order:

Asparagus
Beans
Blackcurrants
Blueberries and many other berry fruits
Broccoli, kale and other brassicas
Fruit juices especially blackcurrant and grape
Onions, garlic
Peppers
Prunes
Raisins
Red wine
Silverbeet/spinach
Tea
Watercress
Wholemeal, wholegrain or fruit breads