Dr Justine Butler explains what they are, how they help us and where to find them.
It was November and I was throwing a ‘Mexican Day of the Dead’-themed party. I’d spent much of the afternoon mashing avocados and was really pleased with my big bowl of vibrant green guacamole which I set aside for later. Come the party, it had turned into a dull, unappetising grey sludge — I’d forgotten to add lime juice.
The discolouration was a natural reaction between the avocado and oxygen, a process called ‘oxidation’. It’s the same thing that causes apple slices to brown when they’re exposed to the air and a similar process takes place on your car when rust forms on patches of bare steel exposed to oxygen and moisture.
Lemon and lime juice stop fruit going brown because they contain vitamin C — a powerful antioxidant which, as it says, prevents oxidation. Your car may need a little more attention than just citrus juice, however!
In our bodies, antioxidants are often said to ‘mop up’ destructive molecules known as free radicals, which can damage parts of our cells by the process of — you’ve guessed it — oxidation.
When free radicals oxidise important parts of a cell, like proteins, DNA and cell membranes, they may lose their ability to function normally and may even die. This could cause a mutation in your DNA or make LDL (bad cholesterol) more likely to become trapped in an artery wall.
Free radicals are produced naturally just by breathing, moving and when your body converts food into energy. But they are also generated in much higher numbers by alcohol consumption, cigarette smoke, pollution, pesticides, ultraviolet light, stress, lack of sleep and fried foods — especially meat.
Antioxidants have the amazing ability to disarm free radicals before they have a chance to damage our cells — just think of them as the cavalry, charging to the rescue!
There are hundreds of different substances that can act as antioxidants in foods — especially in plant foods. The better-known ones are the ACE vitamins A (beta carotene), C and E, plus selenium, lycopene and polyphenols, but there are many, many more.
We’ve known about antioxidants since the 1990s, when research revealed how people with low intakes of antioxidant-rich fruit and vegetables had a higher risk of atherosclerosis, where arteries become clogged with fatty substances, certain cancers, sight loss and a host of other chronic conditions.
Since then, all manner of health claims have been made for antioxidants and global sales of supplements have soared. While it’s widely recognised that diets rich in antioxidant-containing plant foods lower the risk of disease, current evidence doesn’t support the use of antioxidant supplements. There is no magic bullet to good health and high doses of antioxidant supplements may even be harmful in some cases.
High-dose beta-carotene supplements have, for instance, been linked to an increased risk of lung cancer in smokers, while high doses of vitamin E may increase the risk of prostate cancer and haemorrhagic stroke.
Antioxidant supplements may also interfere with certain medications — vitamin E has a blood-thinning effect that could lead to problems in people taking the anticoagulant Warfarin.
It’s easy to imagine the battle between antioxidants and free radicals as one of good versus evil but it’s a bit more complicated than that. We’re beginning to realise that free radicals at low levels are not all bad — they can help destroy invading pathogenic microbes, such as bacteria and viruses, as part of our body’s natural defence mechanism and people who have defects in this system tend to suffer persistent infections.
Other recent evidence shows that free radicals also act as signalling molecules involved in many important functions, including making the heart beat with the correct force. So, at low or moderate levels, free radicals are vital to human health.
The key factor that determines our risk of disease is our entire diet, with plant foods exerting a protective and beneficial effect. The high antioxidant content of vitamins A, C and E and polyphenols in fruits and vegetables may be one of the main reasons. So, if you’re sick, stressed or tired, reach for the broccoli and blueberries!
The best fruit and veg to go for are the brightly-coloured varieties to optimise your antioxidant intake — sweet potato, carrots, red peppers, purple sprouting broccoli, red cabbage, asparagus, curly kale, berries and avocados. And don’t forget the lime juice when you’re making guacamole!
Antioxidants in food
Most antioxidants in nuts are found in the outer skin, for example in almonds, pecans and walnuts. Brazil nuts are an exceptional source of the antioxidant selenium — two a day can increase blood levels by over 60 per cent.
Berries are a very good source, especially blackcurrants, strawberries, blackberries and cranberries. Those that don’t go brown when exposed to air, such as mango, kiwi and orange, contain more antioxidants than those that do (apple, pear and banana).
Good sources include artichokes, curly kale, red and green chilli, black and green olives, red cabbage and beetroot.
Black tea, green tea, red wine, grape juice and coffee all contain significant amounts but obviously wine, tea and coffee should be drunk in moderation because of the alcohol and caffeine content respectively. Water contains no antioxidants and cow’s milk is close to zero.
Wholemeal bread, brown rice and wholegrain pasta contain far more antioxidants than their white, processed equivalents.
Chocolate can be a rich source of antioxidants, but it has to be dark — the more cocoa, the better — so go for 75-99 per cent if you can.
Herbs and spices
Rich in antioxidants — especially cloves, peppermint, allspice, cinnamon, oregano, thyme, sage, rosemary and saffron. Experiment and be generous with your seasoning!
In the pink
Lycopene gives red and pink fruit and veg their colour and cooking boosts levels. Best sources are tomatoes and tomato products — organic ketchup may contain up to three times as much lycopene as non-organic. It’s also found in pink grapefruit, watermelon and guava.
By Dr Justine Butler, Senior Health Researcher at Viva!.