The term phytonutrients refers to certain components of plants that are beneficial and in fact essential for human health. Fruits and vegetables are an excellent source of a variety of these nutrients.
Each type of fruit or vegetable can easily be a source of hundreds of different phytonutrients. Some of these have been quite well researched and others are hardly understood at all.
Plants make these compounds for their own protection – they need antioxidants to be present at all times, and they also need protection against diseases caused by bacteria, fungi and viruses.
Fortunately, we can get the same benefits by eating these fruit and vegetables. In fact, research has shown that humans can protect themselves against heart disease and cancer by getting adequate amounts of phytonutrients in their diets.
We look briefly at some common classes of phytonutrients below.
To see the place of fruit and vegetables and their phytonutrients on the recommended food pyramid, click on our Nutrition and Food page.
We look briefly at some common classes of phytonutrients below.
Carotenoids are phytonutrients that are mostly found in fruits and vegetables that are bright red, orange and yellow.
More than 600 different carotenoids have been identified, and there are probably many more still to be discovered. Some examples are: alpha- and beta-carotenes in carrots, lutein in leafy greens such as spinach and kale, lycopene in tomatoes, watermelon and pink grapefruit and zeaxanthin from citrus and green vegetables.
What they do
The major functions of these phytonutrient compounds in human health are as follows:
* Carotenoids are potent antioxidants. They are fat soluble, so they work as antioxidants in the fatty membranes of cells.
* Carotenoids are precursors of Vitamin A. The carotenes, for example, can be converted to Vitamin A within the body, based on demand for this vitamin.
* They are essential for healthy eyes. One role is to absorb dangerous incoming light rays thereby protecting the retina from damage.
* Carotenoids are necessary for a healthy immune system.
* They are involved in communication between neighbouring cells. As a result, carotenoids are important as protection against cancer, heart disease and eye diseases such as macular degeneration.
When it was discovered that the French diet included much more butter (four times) and much more other animal fats (three times) than the average American diet, but that the French are 2.5 times less likely than Americans to die of coronary heart disease, researchers sat up and took notice.
This relative health of the French despite an apparently less than ideal diet has been called the ‘French paradox’.
This is believed to be due to the protective nutrients present in their typical diet of abundant fruits, vegetables, legumes and grains, olive oil, dairy products.
Red meat and poultry are eaten sparingly, and red wine is consumed regularly but in low to moderate quantities. Fish is also consumed regularly, providing a good supply of Omega-3 oils.
As interest in this type of diet grew researchers began to investigate what was actually contributing to the health benefits.
Amongst other things, they identified that the diet is rich in certain important phytonutrients (derived from plants), including flavonoids, that come from the dark red, purple and green fruits and vegetables.
Many of these compounds have been recognised as strong antioxidants. Antioxidants protect our cells from the problems of oxidation that are a side effect of metabolism – uncontrolled oxidation leads to all the degenerative diseases such as cancer and cardiovascular disease.
Types of flavonoids
Flavonoids belong to a family of phytonutrients called polyphenols. More than 4,000 different flavonoids have been identified so far.
They are essential in a wholesome diet to promote health and prevent disease. They divide into several categories including the following:
* Anthocyanidins which come from red, blue and purple berries and grapes;
* Flavanols (catechins and proanthocyanidins in particular) which come from green tea, chocolate, apples, berries and grapes;
* Flavonones which come from citrus fruits;
* Flavonols which come from a wide variety of foods including yellow onions, scallions, kale, broccoli, apples, berries, teas;
* Flavones from cereals, herbs (parsley, thyme, celery), hot peppers;
* Isoflavones from soybeans, soy foods, legumes.
So what do the flavonoids do?
* They are antioxidants. One way in which they might pay this role is to act as a chelating agent to binds metals such as iron and copper which can cause the formation of free radicals.
Since they are water soluble, these phytonutrients perform this function in the aqueous (watery) parts of cells.
* They are involved in inter-cell communications which have the effect of regulating cell proliferation, growth and death.
Prevention of cancer (uncontrolled cell proliferation) is therefore a possibility, and research has found that it happens in a variety of ways.
Flavonoids stimulate the activity that results in the identification, and excretion of potentially toxic or carcinogenic agents. They preserve the normal cell cycle, ensuring the removal of cells with defective DNA. They slow the rampant proliferation of cancerous cells and speed up the death of such cells (known as apoptosis).
These phytonutrients inhibit the ability of cancerous cells to invade normal tissue and produce tumours, and they inhibit the formation of blood vessels within the tumorous tissue (called angiogenesis). This means that nutrients are not provided to the tumour, and it can no longer flourish.
* They are good anti-inflammatory agents. As you know, inflammation is the body’s normal response to damage or invasion of dangerous infectious agents. However, when it gets out of control it causes many undesirable side effects. So, effective anti-inflammatory agents are a vital part of the whole nutritional package.
The anti-inflammatory role is beneficial in slowing cell proliferation and angiogenesis, as well as reducing the incidence of cardiovascular disease. In cardiovascular disease inflammation causes the deposition of plaque on the arterial walls, leading to blockage of the blood vessel and thrombosis or stroke.
* They act synergistically with Vitamin C each one improving the antioxidant power of the other. Interestingly, this relationship between Vitamin C and flavonoids (especially hesperidin, rutin and quercetin) was discovered as early as the 1930s by Dr. Albert Szent-Gyorgyi, a Nobel Prize winning researcher into Vitamin C.
He discovered that if flavonoids were also present in a Vitamin C preparation it worked much more effectively in treating patients with cardiovascular problems. Some further actions include lowering of cholesterol levels, improving circulation, supporting healthy collagen thereby preserving healthy capillaries, preventing bruising, pain relief, reduced incidence of cataract formation, an antibacterial effect and reduction of allergies and asthma.
* Flavonoids also reduce the stickiness of platelets, thereby reducing the risk of blood clots.
* Isoflavones resemble oestrogen. They improve bone density, fight against hormone-senstitve cancers (breast and prostate) and play a role in lowering cholesterol levels.
* Catechins. You may well have heard that drinking green tea is good for you. In fact, the people of China and India have been doing so for at least 5000 years and found it to be an aid to good health! Science now tells is that the important chemicals in tea (and chocolate!) are the catechins. These compounds are powerful antioxidants which have a positive effect on ones health in a number of ways:
o They have been found to inhibit the development of cancers by acting on certain enzyme systems and repairing faulty DNA.
o They have a positive effect on the health of the heart and cardiovascular system for example by reducing plaque formation in blood vessels, by regulating the tone and elasticity of the blood vessels and by reducing the aggregation of platelets and clot formation.
o They have antibiotic properties by interfering with bacterial DNA replication.
Some flavonoids deserve individual attention!
Resveratrol: the new next best thing.
It was only a matter of time before one of the phytonutrients was isolated and singled out for special attention. This is where the story of resveratrol begins.
It is a compound found predominantly in red grapes, and therefore red wine, raisins, blueberries, cranberries, mulberries and red/purple grape juice (and, incidentally in peanuts!), and is the subject of a great deal of research, the results of which are hitting the scientific press at the present time. Some examples are given below:
* Cancer. For example, resveratrol has been shown to be toxic to be selectively more toxic towards malignant cells than healthy cells – something that is not true for chemotherapy where healthy cells are killed as effectively as the malignant ones.
In experiments with mice resveratrol appears to slow the growth of prostate and breast tumours significantly. And it seems that resveratrol can protect the skin from developing skin cancer due to exposure to harmful rays of the sun!
* Cardiovascular health. Resveratrol acts in a number of ways to keep ones cardiovascular system healthy:
o It is able to prevent the formation of blood clots, so it prevents thrombosis and stroke. This is achieved by reducing the stickiness of platelets in the blood.
o Resveratrol promotes angiogenesis which is the growth of new blood vessels to the heart when the existing ones can no longer carry enough oxygenated blood to the heart.
o Resveratrol controls the levels of low density lipoproteins – the bad fats which tend to clog up ones arteries.
o Resveratrol can control blood pressure and heart rate.
o Resveratrol might improve blood flow by relaxing smooth muscle of the arteries, reduce incidence of irregular heart beats and protect against circulatory damage caused by high blood sugar levels,
* Anti-ageing. Evidence is accumulating which suggests that resveratrol is capable of slowing down the ageing process. Not very long ago scientists identified a ‘longevity’ gene. It was shown that when mice were fed calorie restricted diets (meaning that they were kept a little bit hungry) they lived longer.
This effect has since been shown in many different organisms, including humans. What happens is that under stress, genes are switched on which produce proteins called sirtuins, and these promote the breakdown and metabolism of stored fat to boost energy supplies (so that you are better able to hunt for food!).
Along with this comes better fat and cholesterol metabolism, improved immunity, a healthier cardiovascular system and, indeed, an extended lifespan – that is, an anti-ageing effect! The good news is that starvation is not the only way to switch on sirtuin production! Resveratrol can do the same thing!
* Improved bone health. Resveratrol plays a role in protection of joints and spinal discs.
* Eye health. Resveratrol reduces the incidence of cataracts.
Indoles and isothiocyanates
Indoles and isothiocyantes are phytonutrients that occur in the cruciferous vegetables, including broccoli, cabbage, Brussels sprouts, cauliflower, kale, bok choy and turnips.
They have a cancer-protecting role. One way in which this is achieved is to promote the destruction of cancer-causing agents (carcinogens).
Another is by preventing the multiplication of cancerous cells and promoting apoptosis (cell death). In addition, they inhibit angiogenesis which is the formation of new blood vessels needed to feed growing tumours.
As a result they reduce the ability for cancer cells to invade normal tissue.
These compounds also appear to play a role in oestrogen metabolism and have a positive effect in oestrogen-dependant cancers.
Allium and other sulfur-containing substance come from onions and garlic and related vegetables. This family of phytonutrient compounds has been found to have many health benefits:
* Cardiovascular health: decreased cholesterol synthesis, decreased platelet aggregation, decreased atherosclerosis, relaxation of blood vessels (decreased hypertension) and decreased inflammation which contributes to heart disease.
* Cancer prevention: This is achieved in a variety of ways. For example, the formation of carcinogens is inhibited and toxins are eliminated more effectively, unregulated cell division is minimized, the destruction of damaged cells (called apoptosis) is stimulated.
* Infections are minimized through the antiviral, antibacterial and anti-parasitic activity of garlic. This leads to fewer respiratory ailments (e.g. colds and flu, TB, pneumonia, bronchitis and even asthma), digestive disorders (e.g. diarrhoea, worms and parasites and stomach ulcers) and skin problems (e.g. boils, acne, eczema, insect bites and stings and fungal infections).
You may well have heard that drinking green tea is good for you. In fact, the people of China and India have been doing so for at least 5000 years and found it to be an aid to good health!
Science now tells is that the important chemicals in tea (and chocolate!) are the catechins. These compounds are powerful antioxidants which have a positive effect on ones health in a number of ways:
* They have been found to inhibit the development of cancers by acting on certain enzyme systems and repairing faulty DNA.
* They have a positive effect on the health of the heart and cardiovascular system for example by reducing plaque formation in blood vessels, by regulating the tone and elasticity of the blood vessels and by reducing the aggregation of platelets and clot formation.
* They have antibiotic properties by interfering with bacterial DNA replication.
Ellagic acid, which is present in berries, pomegranates and nuts, is another compound with special health benefits.
* It has a protective effect against cancer as it is an antioxidant as well a being able to prevent abnormal cell proliferation.
* It contributes to heart health by reducing blood pressure and preventing the thickening of blood cell walls.
* It also contributes to the health of the brain as it ages.
Lest you think that you are getting enough of these nutrients consider the following statistics, and see how you fare:
The average American consumes 3.3 servings of vegetables per day. Dark green and deep yellow vegetables are largely missing.
Only 49 % of the population gets this amount. About 10 % of the population only manages 1 serving per day!
Only 29 % of the population gets the minimum recommendation of fruit per day (2 servings), with about 48 % consuming less than 1 serving of fruit per day!
All fruits and vegetables are certain to be beneficial, but some have been studied extensively and found to be particularly important. These include the following, colour-coded for convenience!
Red fruits and vegetables
o Red peppers
Orange and yellow fruits and vegetables
o Citrus fruits
o Tropical fruits like papayas
Green fruits and vegetables
o Cruciferous vegetables which include cabbage and broccoli
o Green, leafy vegetables
Blue/purple fruits and vegetables
White/brown fruits and vegetables
o Garlic, onions and related vegetables
If there is any danger that you or your family are falling short of these sources of essential phytonutrients on a daily basis, some form of supplementation is advised.
We have found that, even armed with knowledge and the will to ‘do it right’, we are unable to fulfil all our dietary needs for phytonutrients(for a whole host of reasons).
We believe that our best insurance policy, therefore, is to take supplements on a daily basis, at the same time as eating the best diet possible.