What are antioxidants?

What do they actually do? How can you ensure you get enough?

When you hear the term “antioxidants”, you may think it’s just another nutrition catchphrase. However, antioxidants are really important in your diet: they’re a powerful preventative measure against disease.

Antioxidants thwart cell damage

Millions of processes requiring oxygen occur in the body on a daily basis, explains Dr Claudia Fajardo-Lira, Professor of Food Science and Nutrition at California State University-Northridge.

Oxidants, also called free radicals, are molecules that occur naturally in the body as by-products of oxygen usage. Other external factors such as sun exposure, air pollution and tobacco smoke can also introduce free radicals in the body, triggering damage to tissues, cell walls, cell structures and even cell DNA through a process called oxidation.

This damage by free radicals can speed up the ageing process and is believed to play a role in the development of many different chronic diseases, including cancer, certain eye diseases, diabetes, heart disease, Parkinson’s disease and Alzheimer’s disease.

Fortunately, there’s a way of slowing down this destructive process: by getting enough antioxidants.

“Antioxidants are compounds in foods that neutralise free radicals in the human body by binding to oxidants,” explains Professor Tim Crowe of the School of Exercise and Nutrition Sciences at Australia’s Deakin University.

Go for antioxidant-rich plant foods

Both Crowe and Fajardo-Lira stress the importance of antioxidants in overall health, with Prof Crowe adding that everyone should get plenty of antioxidants from their diet because they’re an important part of the body’s immune defence.

They say the best antioxidant sources are fruits, vegetables and other plant foods such as herbs, spices, nuts, seeds and legumes. Antioxidants are also found in green tea, black tea, red wine and dark chocolate.

According to Fajardo-Lira, the best way to get the optimal amount of antioxidants in your diet is to ensure you consume a wide variety of fruits and vegetables with different colours. The colour usually indicates a specific antioxidant. An added bonus is that most antioxidant-rich foods are also good sources of vitamins, minerals and fibre, while being low in cholesterol and saturated fat.

But even though numerous research studies and a lot of media buzz have highlighted the benefits of antioxidants, the message still isn’t quite getting through. The recently published Australian Health Survey notes that people are eating less fruit and vegetables, with only 6.8% eating the recommended number of servings of fruit and vegetables each day.

How antioxidants are measured

With so many foods containing antioxidants, it is a good idea to know which foods are particularly good antioxidant sources. Fortunately, health scientists are devising ways in which to measure the total antioxidant capacity (TAC) of different foods.

Currently, there are several different ways to measure the antioxidant value of foods, but according to Prof Crowe, the most common is a laboratory-based test known as the Oxygen Radical Absorbance Capacity (ORAC) method. This unit of measurement for antioxidants was developed by the US National Institute on Ageing at the US National Institutes of Health (NIH).

Most ORAC value lists compare each food’s ORAC content based on a standard weight of 100g; other rankings use “typical serving size”. Values are expressed in units of ?mol TE/100g (micromol Trolox Equivalent per 100g), with nutrition scientists using Trolox equivalency as a benchmark for the antioxidant capacity of a food. The idea is to focus on foods that have an ORAC rating of at least 1 000 per 100g. The higher the food’s ORAC value, the more antioxidants it contains.

Nutrition scientists stress that ORAC values should be used as a rough guideline only.

How much is enough?

In the absence of a set Recommended Daily Allowance (RDA) for antioxidants, the World Health Organisation (WHO) recommends a daily intake of five to eight portions (400g to 600g) of fruits and vegetables.

Put differently, try to pile up half your plate with a wide variety of antioxidant-rich fruit and vegetables at meals.

Particularly good antioxidant sources

To get you on the right track, here are some foods that pack a powerful antioxidant punch:

- Prunes – 14 582 ?moles (TE/100g)
- Wild blueberries – 13 427 ?moles (TE/100g)
- Blackberries – 7 701 ?moles (TE/100g)
- Raspberries – 6 058 ?moles (TE/100g)

Other good antioxidant-rich fruits are acai berries, oranges, cherries, kiwi, pineapple, elderberries, goji berries and apples. According to an article in the Nutrition Journal, berries should be eaten fresh, dried or frozen for maximum antioxidant content and nutritional value.

Herbs and spices
With a whopping ORAC value of 314 446 ?moles (TE/100g), dried and ground cloves have the highest antioxidant content of more than 400 herbs and spices, according to the USDA ORAC database.

This is followed by ground cinnamon, dried oregano and ground turmeric. Certain dried spices like parsley, chives, basil, oregano and dill have higher antioxidant levels than the fresh versions.

Nuts and seeds
Walnuts top the list of tree nuts for antioxidant content, followed by pecans and chestnuts. However, pistachios, hazelnuts and almonds also contain antioxidants.

If you’re not keen on nuts, rather have sesame or sunflower seeds.

Artichokes, okra, kale and bell peppers top the list of vegetables high in antioxidants. Other good options include asparagus, broccoli, red cabbage, Brussels sprouts, alfalfa sprouts, tomatoes, raw onion, sweet potato, red cabbage, eggplant, raw garlic and spinach.

Conventional boiling of almost all vegetables can reduce the ORAC value up to 90%, so rather steam your veggies to retain most of their antioxidants.

Small red beans and kidney, pinto and black beans are rich sources of antioxidants.

Green tea, coffee, red wine and fruit juices like cranberry, grape juice and pomegranate juice have significant ORAC scores.

Unsweetened, dry cocoa powder has an ORAC value of 80 933 ?moles (TE/100g) compared to ditched cocoa powder, which has a value of 40 200 ?moles (TE/100g), and dark chocolate which has a value of 20 823 ?moles (TE/100g).

If you can’t do without your chocolate fix, aim to have one row or 25g of dark chocolate two to three times a week.

- Cleveland clinic: http://my.clevelandclinic.org/services/heart/prevention/nutrition/food-choices/anti-oxidants
- Rodriguez-Casado A:IMDEA Food Institute, Madrid, Spain. “The Health Potential of Fruits and Vegetables Phytochemicals: Notable Examples.” Crit Rev Food Sci Nutr. 2014 Sep 16:0. [Epub ahead of print] http://www.ncbi.nlm.nih.gov/pubmed/25225771
- Howes MJ, Simmonds MS. “The role of phytochemicals as micronutrients in health and disease”.Curr Opin Clin Nutr Metab Care. 2014 Sep 23. [Epub ahead of print]
- Mayo Clinic: “A Grocery Bag of Beneficial Antioxidants” http://healthletter.mayoclinic.com/ Nov 25, 2013.
- Mayo Clinic: "Antioxidants: Preventing Diseases, Naturally." ScienceDaily, 13 September 2007. www.sciencedaily.com/releases/2007/09/070908001613.htm
- http://naturalrevolution.org/10-highest-antioxidant-foods-in-the-world/#cwCBcCFtrKA4eM62.99
- http://www.ars.usda.gov/SP2UserFiles/Place/12354500/Articles/AICR07_ORAC.pdf
- http://en.wikipedia.org/wiki/Oxygen_radical_absorbance_capacity

Image via Thinkstock.

[hr style="single"]Read more about antioxidants:

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>> Nutrients and heart disease

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