Ever wondered why lemon juice stops chopped apple going brown? It’s because it contains vitamin C – an antioxidant that protects food from spoiling when it’s exposed to air. A similar process takes place on your car when rust forms on the bare steel when it’s exposed to oxygen and water – although rescue will take a bit more than lemon juice in this case.
Can oxygen be harmful?
It’s ironic that oxygen, an element essential for life, can have a similar damaging effect on the body. ‘Oxidative stress’ is thought to play a role in aging, leading to wrinkled skin and brown skin patches, eye diseases such as cataracts and age-related macular degeneration plus a number of chronic diseases, including heart disease, cancer, diabetes, Alzheimer’s and Parkinson’s disease.
Now for the science!
The culprits responsible for this mayhem are called reactive oxygen species or free radicals. These oxygen-containing molecules have at least one unpaired electron and electrons like to travel in pairs. So when they find themselves all alone, they try to snatch a partner from another molecule, and they’re not fussy – an electron from a cell wall will do just fine even though it may cause that cell to die. Snatching one from your DNA may cause a mutation that leads to cancer – but balance is everything to a free radical. They can also make LDL (‘bad’) cholesterol more likely to get trapped in an artery wall and that’s not good! In fact, free radicals can leave a trail of destruction if left to run riot.
Free radicals are naturally formed when you breathe, exercise 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.
So how do you combat them? The main defenders against free radicals are antioxidants that go around balancing and disarming them by donating an electron but without turning into electron-scavenging substances themselves.
There are a multitude of antioxidants in foods – especially in plant foods. The better-known ones include: vitamins A (beta carotene), C and E, selenium, lycopene and polyphenols but there are many, many more.
Antioxidants gained attention in the 1990s when we began to understand how free radical damage was involved in atherosclerosis, where arteries become clogged with fatty substances. But they were also thought to contribute to cancer, sight loss and a host of other chronic conditions. Studies revealed how people with low intakes of fruit and vegetables, which are rich in antioxidants, were at greater risk of developing these conditions than those who ate plenty of fruit and veg.
A study looking at the antioxidant content of more than 3,000 foods, drinks, spices, herbs and supplements used worldwide found that plant foods were by far the richest source and that meat, fish and dairy foods are low in antioxidants. The researchers concluded that “A plant-based diet protects against chronic oxidative stress-related diseases”.
Where to find antioxidants
There’s no doubt that fruit and vegetables are an excellent source and you can safely eat as much as you like – aim for 8-10 portions a day, the more the merrier! However, it’s not just the quantity that matters but the quality. Choose brightly-coloured varieties to optimise your antioxidant intake – sweet potato, purple sprouting broccoli, red cabbage, asparagus, curly kale, berries and avocados.
Berries are a particularly good source, especially blackcurrants, strawberries, blackberries, goji berries and cranberries. A handy tip for fruits in general: those that don’t go brown when exposed to the air, such as mango, kiwi and orange, contain higher levels of antioxidants than those that do – apple, pear and banana.
But don’t forget your veggies! Good sources include artichokes, curly kale, red and green chili, black and green olives, red cabbage and beetroot.
Herbs and spices are also great providers, particularly clove, peppermint, allspice, cinnamon, oregano, thyme, sage, rosemary and saffron.
Nuts can be good too, although most antioxidants are found in the outer skin, for example in almonds, pecans and walnuts. Brazil nuts are an exceptional source of the antioxidant selenium. Just two a day can increase the amount of this mineral in your blood by over 60 per cent.
Wholegrain foods such as wholemeal bread, brown rice and wholegrain pasta contain far more antioxidants than their white processed equivalents.
Chocolate can be a rich source too but it has to be dark chocolate – the more cocoa, the better – go for 75-99 per cent.
Lycopene is a pigment that helps give red and pink fruit and vegetables their colour. Part of the carotenoid family, cooking can actually boost the levels. Best sources are tomatoes and tomato products but it is also found in pink grapefruit, watermelons, guava and papayas. Brings new meaning to staying in the pink!
Water contains no antioxidants, cola and cow’s milk are also close to zero. Black tea, green tea, red wine, grape juice, espresso and black coffee all contain significant amounts but matcha tea (made out of powdered green tea leaves) and hibiscus tea (eg Wildberry Zinger) come out ahead of the pack with extremely high levels of antioxidant activity.
What about supplements?
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 either in the general population or in people with diseases. It’s best to get your antioxidants from a diet rich in fruit and vegetables rather than from supplements. There is no magic bullet and high doses of antioxidant supplements may even be harmful.
Studies have linked high-dose beta-carotene supplements to an increased risk of lung cancer in smokers while high doses of vitamin E have shown an increased risk of prostate cancer and haemorrhagic stroke – a type of stroke caused by bleeding in the brain. It might be that antioxidant supplements interfere with some medications. For example, vitamin E has a blood-thinning effect that could lead to problems in people taking anticoagulants such as Warfarin.
However, free radicals at low levels are not entirely bad and can play a useful role in our bodies. They destroy invading pathogenic microbes as part of our body’s own defence mechanism and people who have defects in this system tend to suffer from persistent infections. Recent evidence shows that free radicals also act as signalling molecules involved in many different important functions, including making the heart beat with the correct force. In short, free radicals at low or moderate levels are vital to human health.
Compelling evidence shows that the whole diet is a crucial factor in the control of chronic disease, with plant foods exerting a protective effect. The high content of natural antioxidants (vitamins A, C, and E and polyphenols) in fruits and vegetables may be a main factor responsible for these effects. Free radicals and antioxidants are both important to health, the key is to balance the two and remember, if you’re sick, stressed or tired – reach for the blueberries!