Phytochemicals and antioxidants

Phytochemicals, also called phytonutrients, are naturally occurring plant chemicals that can have protective qualities for human health.

Plants produce these chemicals to help protect themselves, for example by making the plant unattractive to insect pests. They also provide the plant with its colour, flavour and smell.

Where are they found?

Phytochemicals are found in unprocessed or minimally processed plant foods, including fruits, vegetables, grains, beans, legumes, herbs, spices, nuts, seeds and other plants.

What do they do?

Thousands of phytochemicals have now been identified. Many of these have antioxidant activity. An antioxidant is a compound that prevents another molecule from becoming oxidised. When molecules in the body become oxidised, free radicals can be formed. Free radicals are very unstable and cause damage within the body as they break down.

Antioxidants stabilise free radicals and prevent this damage by donating electrons.

There are many different groups of phytochemicals which all have different chemical structures. These different types are metabolised differently in the body and may induce different health effects. Examples of phytonutrients include:

• Flavonoids (For example, anthocyanins and quercetin): found in soybeans, onions, apples, tea and coffee
• Polyphenols (For example, resveratrol and ellagic acid): found in green tea, red wine, grapes, berries and wholegrains
• Carotenoids (For example, lycopene, lutein, zeaxanthin, beta-carotene): found in red, dark green and orange fruits such as tomatoes, carrots, sweet potatoes, watermelon, leafy greens.

Should I eat foods with phytonutrients?

Consumption of phytochemicals has been associated with reduced risk of certain chronic diseases including cardiovascular disease (heart disease and stroke), cancer and age-related eye disease.

Those who eat the number of recommended serves of fruit and vegetables each day will have higher intakes of phytochemicals and this will benefit their overall health.

It is important to remember that nutrition and food scientists are still discovering and learning more about phytochemicals, including identifying new ones. It has become clear that phytochemicals are absorbed best by the body when they are eaten as whole foods rather than when they are isolated and taken as pills or other supplements.

In supplement form an excessively high dosage can even be harmful.

What evidence is there?

Evidence is also accumulating to show that different types of phytochemicals interact beneficially with each other. So to get the full benefit from phytochemicals it is important to obtain them from a wide variety of different foods each day.

Phytochemicals in foods are easily destroyed by long periods of heating or by many types of food processing. For this reason, it is important to eat fresh fruit and vegetables and other foods that are either raw or lightly cooked or minimally processed.

Talking point

Within the Comments, consider sharing with other learners you thoughts on the following question:

• What are some other examples of phytochemicals and which foods they can be found in?

You might like to take some time to read comments made by other learners, and if you find these comments interesting, respond to them. Remember you can also ‘Like’ comments or follow other learners throughout the course.

Find out more

In the See also section of this step, you can access a link to articles that discuss phytonutrients and antioxidants and the role they play in health and disease prevention.