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 making the plant unattractive to insect pests. They also provide the plant with its colour, flavour and smell.
Phytochemicals are found in unprocessed or minimally processed plant foods, including fruits, vegetables, grains, beans, legumes, herbs, spices, nuts, seeds and other plants.
Thousands of phytochemicals have now been identified. Many of these have antioxidant activity. An antioxidant is a compound that prevents another molecule 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:
- Flavanoids (e.g. anthocyanins and quercetin) found in: soybeans, onions, apples, tea and coffee.
- Polyphenols (e.g. resveratrol and ellagic acid) found in: green tea, red wine, grapes, berries and wholegrains.
- Carotenoids (e.g. lycopene, lutein, zeaxanthin, beta-carotene) found in: red, dark green and orange fruits such as tomatoes, carrots, sweet potatoes, watermelon and leafy greens.
Consumption of phytochemicals has been associated with reduced risk of certain chronic diseases including certain 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.
Nutrition and food scientists are still discovering and learning more about phytochemicals. 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.
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 and minimally processed.
From the Food As Medicine course by Monash University.