We often hear about the benefits of eating antioxidant-rich foods to help fortify our bodies against illness and improve our health. But exactly what are the benefits of soaking up these substances, and how do you know you're getting enough? The best way to answer this question may be to go back to body basics.

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Antioxidants are naturally occurring compounds found in many foods we eat and drink, such as fruits, vegetables and tea. In the body, they help counter the negative effects of oxidising free radicals, which form during normal metabolism and through external factors, including X-rays, pollution and ultraviolet radiation. A bit like political fanatics, free radicals are inherently unstable, as they contain 'extra' energy, which they seek to offload by reacting with other chemicals in the body; in the process, they interfere with your cells' ability to function. This chemical reaction—oxidation—is vital for life; our bodies use it to kill bacteria and other microbes that cause illness. But when oxidising reactions get out of control, disease can occur.

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The role of antioxidants

Your body produces several antioxidant enzymes that help prevent or suppress excessive oxidation, and many compounds in a healthy diet aid this process. A typical antioxidant enzyme in the blood is superoxide dismutase, and one of the main antioxidant compounds in your diet is natural vitamin E. We draw hundreds of known antioxidant compounds from food, and there may well be thousands that are important for optimal health. (It's one of the reasons we should eat a variety of foods—to improve our chances of picking up as many helpful compounds as possible.) Plants themselves produce antioxidants to guard against harsh environmental conditions; for example, antioxidants protect leaves from sun damage and exist in high concentrations in fruit to prevent it from becoming rancid. Interestingly, in times of water and heat stress, plants can produce antioxidant compounds in abundance. The cultivation of grapes and olives clearly documents this phenomenon.

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Antioxidant benefits

Population studies clearly show the protective effect that antioxidants have against heart disease and cancer. These studies examine individuals whose diets contain a high proportion of fresh fruits and vegetables, which are in turn associated with a high intake of natural antioxidants. In fact, a generally healthy diet high in antioxidant-rich fruits and vegetables is as important in protecting your body against disease as exercising, maintaining a healthy weight and being a nonsmoker. The development of several diseases, including cancer and heart disease, has implicated oxidising free radicals, highlighting the need to consider adding antioxidants to your diet as a preventive medicine.

Can you bottle that goodness?

When you plan to increase your intake of a particular nutrient, it can seem easiest to reach for a pill. Since the discovery of vitamins 100 years ago, ongoing controversy has surrounded the idea of trying to prevent deficiencies or diseases by taking various vitamins and antioxidants as supplements, often in greater concentrations than necessary. Over the past few decades, many trials have assessed the benefits of taking antioxidant vitamin or mineral tablets.

Large trials rarely show effective antioxidant supplementation, and, in some cases, supplements may even cause harm. For example, taking betacarotene supplements may increase the risk of lung and prostate cancer. One trial randomly divided 11,324 patients with pre-existing heart problems into four groups: those taking 300 mg of vitamin E, those taking 850 mg of naturally occurring omega-3 fatty acids (fish oil), those taking both and those offered neither. After 3.5 years of follow-up, the fish oil clearly showed its power to prevent heart attacks and strokes, but the vitamin E produced no discernible benefit. The message is clear—take your antioxidants the way they occur naturally: as part of a diet that's rich in fresh fruits and vegetables. Hippocrates' famous dictum—"Let food be thy medicine"—rings absolutely true.

5 Best Antioxidant Foods

Go for a raw handful for more antioxidants

Black and uncooked is the way to go.

Get your highest vitamin C antioxidant hit eating them raw

Raw onions contain more antioxidants

It provides a bigger boost than white

By David Colquhoun, associate professor and cardiologist at Wesley Medical Centre, Greenslopes Private Hospital and The University of Queensland in Brisbane.