Antioxidants explained

| 5 August 2022
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Often used as a promotional buzzword, are antioxidants all they are hyped up to be?

You can’t beat a big spoonful of vibrant, green guacamole alongside a spicy Mexican vegan chilli. But be careful – it can easily turn into an unappealing grey sludge if you leave it for too long or don’t add enough lime juice. This discoloration is a natural reaction between the avocado and the air, a process called oxidation. The same process causes apple slices to brown when exposed to air.


Oxidative stress

‘Oxidative stress’ happens in our bodies too and is thought to play a role in aging, leading to wrinkled skin and brown skin patches, cataracts and age-related macular degeneration plus a number of chronic diseases, including heart disease, cancer, diabetes and Alzheimer’s disease. It’s ironic that oxygen, an element essential for life, can have such a damaging effect on the body.


Free radicals

The culprits responsible are unstable molecules called free radicals. They are produced naturally just by breathing, moving about and when your body converts food into energy. But are generated in much higher numbers by alcohol consumption, cigarette smoke, pollution, pesticides, ultraviolet light, stress, lack of sleep and fried foods – especially meat!

The destructive capability of free radicals lies in the fact that these oxygen-containing molecules carry a single electron. Because electrons much prefer to travel in pairs, they try to snatch a partner electron from other molecules. They’re not fussy – one from a cell wall will do, even though it may cause that cell to die and taking one from your DNA may cause a mutation that leads to cancer. They can make LDL ‘bad’ cholesterol more likely to get trapped in an artery wall and that’s not good as it can block the blood flow increasing the risk of a heart attack or stroke.


ACE vitamins

There is, however, an antidote. Antioxidants can disarm free radicals before they do any harm and there are hundreds, probably thousands, of different substances that act as antioxidants in food – especially plant foods. The best-known are the ACE vitamins, A (beta carotene), C and E, plus selenium, lycopene and polyphenols, but there are many, many more. Lemon and lime juice prevent oxidation because they contain vitamin C.

We’ve known about antioxidants since the 1990s when research revealed how people with low intakes of fruit and vegetables had a higher risk of atherosclerosis – arteries becoming clogged with fatty substances – certain cancers, sight loss and a host of other chronic conditions. Plant foods are by far the richest source while meat, fish and dairy are low in antioxidants.

A study published in Nutrition Journal looked at the antioxidant content of more than 3,100 foods – drinks, spices, herbs and supplements used worldwide – and found that “plant-based foods introduce significantly more antioxidants into the human diet than non-plant foods”.


Which foods are best for antioxidants?

Berries are an excellent source, especially blackcurrants, strawberries, blackberries and cranberries. Fruits 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. Olives are also a good source. The vegetables to go for include artichokes, kale, red and green chilli, red cabbage and beetroot.

Wholemeal bread, brown rice and wholegrain pasta contain far more antioxidants than their white, processed equivalents.

In nuts, 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 – two a day can increase blood levels by over 60 per cent. Chocolate can be a rich source, but it has to be dark – the more cocoa, the better – so go for 75-99 per cent.

Black and 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, cola and cow’s milk are also close to zero.

Herbs and spices are generally very rich in antioxidants – especially cloves, peppermint, allspice, cinnamon, oregano, thyme, sage, rosemary, saffron, chilli and black pepper. One study found that people who ate spicy foods almost every day had a 14 per cent lower risk of death compared with those who consumed spicy foods less than once a week. Experiment and be generous!

The antioxidant lycopene is a pigment that helps give red and pink fruit and vegetables their colour and cooking actually increases the 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, guava and papaya.

Vitamins A, C and E can be destroyed by long-term storage or prolonged cooking. Although cooking can increase antioxidants in some foods, processed foods generally contain a lot less than fresh foods.

The key factor determining our risk of disease is the whole diet rather than individual elements, with plant foods exerting a powerful, protective effect. The high antioxidant content of fruits and vegetables may be one of the reasons why. So, if you’re sick, stressed or tired – reach for the broccoli and blueberries!


What about supplements?

All manner of health claims have been made for antioxidants and global sales of supplements have soared. But while it’s widely recognised that diets rich in antioxidant-containing plant foods lower disease risk, the evidence doesn’t support the use of antioxidant supplements. There’s no silver bullet and high doses of antioxidant supplements may even be harmful.

For instance, high-dose beta-carotene supplements have 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 – a type of stroke caused by bleeding in the brain.

Antioxidant supplements may also interfere with some medications – vitamin E has a blood-thinning effect that could lead to problems in people taking anticoagulants, such as Warfarin.

It’s easy to imagine the battle between antioxidants and free radicals as one of good versus evil but as is often the case in nutrition science, 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 defense mechanism and people who have defects in this system tend to suffer persistent infections.

Other 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.


Eat the rainbow!

The best way to get the right amount of antioxidants is to eat plenty of brightly-coloured fruit and vegetables – 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!

About the author
Dr. Justine Butler
Justine joined Viva! in 2005 after graduating from Bristol University with a PhD in molecular biology. After working as a campaigner, then researcher and writer, she is now Viva!’s head of research and her work focuses on animals, the environment and health. Justine’s scientific training helps her research and write both in-depth scientific reports, such as White Lies and the Meat Report, as well as easy-to-read factsheets and myth-busting articles for consumer magazines and updates on the latest research. Justine also recently wrote the Vegan for the Planet guide for Viva!’s Vegan Now campaign.

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