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Phytochemicals and phytonutrients

Phytochemicals, also called phytonutrients, are naturally occurring plant chemicals that can have protective qualities for human health.
GARY WILLIAMSON: I’d like to introduce you to the amazing world of phytochemcials. So phytochemicals are found in all of these different fruits and vegetables, like I’ve got in front of me here, and we are beginning to realise how good they are for our health. For some things they make colour, for some things they make a taste. For some things they give that food that particular property. So the phytochemicals themselves can have a whole range of different effects on health. They can affect the digestion and absorption of carbohydrates and sugar, they can slow down the spikes that we get after eating too much sugar, especially reducing the risk of type 2 diabetes.
If we look at the apples, then apples are particularly high in the whole range of different phytochemicals, particularly called polyphenols. Polyphenols are absorbed into the body. They protect against cardiovascular disease and they also have a number of different effects on the blood vessels themselves. So if you increase the diameter of the blood vessels and actually you reduce the blood pressure a little bit which is a good thing. So phytochemicals are also found in vegetables such as peppers. We have tomatoes. Those are particularly high in carotenoids. Those are absorbed quite well into the body, they’re actually fat soluble and they protect against cardiovascular disease. Other phytochemicals are found let’s say in oranges.
So oranges contain a polyphenol called hesperidin, which is also good for blood vessel health. So if we look at something like strawberries or raspberries and some blackberries and blueberries. So those are berry fruits and those are rich in the phytochemicals called anthocyanin. And anthocyanins are thought to be actually quite protective against cardiovascular disease. If we look at some of the other vegetables such as onions, then the main phytochemical there is quercetin. Often in quercetin is thought to be particularly good at preventing, or at least reducing the risk of type 2 diabetes. Quercetin is one of my favorite molecules.
It’s absorbed well into the body and it has a number of different effects on the cells that line the walls of blood vessels. In broccoli, the main phytochemicals present in broccoli, and in other brassica vegetables are called glucosinolates. Now glucosinolates are sulfur containing compounds, which, once they’re absorbed they have a number of different effects, but one of the most interesting effects is to boost our own defences against carcinogens, toxins and environmental pollutants. So they help our body to protect against that sort of threat and therefore the glucosinolates from brassica vegetables are actually quite good at helping to reduce the risk of colon cancer.
We also have to consider how processing can affect some of the phyotochemical content of the fruits and vegetables.
So if we take an example, we take strawberries: they contain lots of anthocyanins, hence the beautiful red color. But if we then process them into jam then they contain a lot less. A lot of the anthocyanins are lost during the processing into jam.
If we take apples: if we process them into apple juice then if we over processed into a long life juice, we can lose a lot of the phytochemicals from apples when we make apple juice. So food processing does have a big effect on the level of phytochemicals in our food that we eat. We can call them phytonutrients when we’re sure that those phytochemicals can have a health benefit. And the health benefit is the thing that we’re particularly interested in, because the health benefit is what allows us to a certain extent, to use phytochemicals in fruits and vegetables as one of the components of our understanding of food as medicine.

Watch Gary provide an overview of phytochemicals, also called phytonutrients, and the crucial role they play in our health and wellbeing.

More about phytochemicals and what they do

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.

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 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

If it’s of interest to you consider reading Phytonutrients and The Nutrition Source – Antioxidants to find out more about phytonutrients and antioxidants and the role they play in health and disease prevention.

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Food as Medicine

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