Dietitians and health fanatics alike spiel forth about the merits of antioxidants (myself included) but what exactly do they do and what is the best way to consume them? Oxidation reactions occur frequently in our bodies and in the environment, often producing free-radicals which can damage cells and lead to oxidative stress.

Oxidative stress is thought to be a factor in a number of diseases including hardening of the arteries, neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease and some cancers.

Antioxidants are substances which can slow down or block these reactions and so theoretically reduce the damaging effects of free radicals.

Many substances have antioxidant properties - most commonly Vitamins A, C, E, beta carotene and selenium. In fact, there are huge numbers of antioxidant phytochemicals in food, but specific details about how they exert their benefits remain hazy.

Population studies associate certain antioxidant containing food or drink with protective effects. The "French paradox" (low incidence of heart disease despite a relatively high fat intake in France) has been linked with consumption of the potent antioxidant resveratrol found in red wine. In China, the lower incidence of stomach and esophageal cancer has been associated with high intake of catechin-rich green tea. We know antioxidant containing foods have health benefits, but this is likely to be a combined effect of phytochemicals, minerals, vitamins and fiber.

The evidence for antioxidant supplements is less convincing. Recent studies have shown no protective effect from supplements against heart disease. More worryingly, some negative health effects have been observed. In 1996, a widely reported long-term study into the effects of beta carotene supplements for smokers was terminated early after the supplement-taking group was found to have a 28 percent higher incidence of lung cancer. Earlier this year, a study linked vitamin A & E and beta carotene supplementation to an increased risk of death.

In Beijing, food sources of antioxidants are easily found. When choosing fruit and vegetables, the more brightly colored the better. Dark green vegetables, especially spinach and broccoli, red peppers, carrots and sweet potatoes are excellent sources of beta carotene. Tomatoes contain large amounts of lycopene - especially protective against prostate cancer. Soy beans and peanuts contain isoflavone phytoestrogens and Vitamin E.

Berries are top of the fruit list, although with strawberry season over, availability is not great. Cherries, which are high in beneficial cyanidins are abundant at present as are the distinctive Chinese bayberry (yangmei), a red spherical berry with a segmented surface and a sweet yet sour flavor. For a blueberry fix, try a delicious blueberry lassi (yoghurt drink) at The Arts Haven Caf on Guozijian. Citrus fruits also score highly, oranges are available year-round, and grapefruits are now instore. Apricots and mangos are also good seasonal choices.

Some anti-oxidants are quickly degraded with cooking, cutting and storage, so try to consume fresh and prepare at the last minute. Polyphenolic antioxidants in whole-grains and green tea are more stable. Don't forget to justify a few squares of dark chocolate and a small glass of red wine for their antioxidant content.

This nutrition-related column is written by Nina Lenton, a qualified dietitian living in Beijing and working at Bayley and Jackson Medical Center. Contact her at nina.lenton@bjhealthcare.com.

(China Daily 06/06/2007 page14)