Phytochemicals are naturally occurring, biologically active chemical compounds in plants. The prefix ‘phyto’ is from a Greek word meaning plant.

The presence of certain types of phytochemicals in some plants can act as a natural defence system providing protection against such things as attack from insects and grazing animals. In contrast, other plants produce phytochemicals that provide colour, aroma and flavour, thus inviting attention from potential consumers.

More than 4,000 of these compounds have been discovered, and it is expected that scientists will discover many more. Any one serving of vegetables could provide as many as 100 different phytochemicals.

Why phytochemicals should be in our diet

When consumed in the diet, there is an increasing body of evidence to indicate that phytochemicals may reduce the risk of age-related chronic diseases such as coronary heart disease, diabetes, high blood pressure and certain types of cancer.

Although their absence from the diet might not cause deficiency symptoms, such as those found with vitamins and minerals, they are thought to be important for health and wellbeing throughout life, especially in adulthood and in the elderly.

Phytochemicals are thought to act as synergistic agents, allowing nutrients to be used more efficiently by the body. Synergy is the working together of two things (food components, for example) to produce an effect greater than the sum of their individual effects.

Phytochemical classification

Phytochemicals can be classified into 3 main families:

Terpenoids such as the carotenoids
Carotenoids such as beta-carotene are responsible for the orange-red colours of popular foods like carrots, oranges and tomatoes. Beta-carotene is converted in the body to vitamin A by a specific enzyme present in the gut.

Phenolic compounds such as the flavonoids
Cyanidin is a polyphenolic compound found in many fruits such as blueberry. The highest concentrations of cyanidin are found in the skins of the fruit.

Alkaloids
Capsaicin is an alkaloid compound found in chill peppers. Because of the burning sensation caused by capsaicin when it comes in contact with mucous membranes, it is commonly used in food products to give them added spice or heat.

Phytochemical action

For over 20 years, it was widely believed that, since most phytochemicals have demonstrated antioxidant activity outside of the body, consuming them would bolster the level of antioxidants in the bloodstream. This would then lead to improved health and wellbeing as well as extending one’s life expectancy.

Now, though, there is increasing evidence from recent research that these potential health benefits arise from mechanisms other than antioxidant capacity alone.

Until these matters are resolved, researchers recommend that a common sense approach should be followed. A balanced diet, rich in fruits and vegetables, will supply all of the phytochemicals needed to assist with the maintenance of health and wellbeing.

Parents who insist on their children eating up all of their vegetables are to be complimented for their good judgement!

Learn about a new apple cultivar with high levels of anthocyanin being developed by Plant & Food Research in this article: Why breed a red fleshed apple.

Nature of science

When faced with a claim that something is true, scientists respond by asking what evidence supports it. In the case of the claim made by some that certain phytochemicals found in fruit and vegetables have antioxidant activity, scientists are continuing to gather evidence.

    Published 18 March 2011