they prevent disease?
In addition to fats,
vitamins, and minerals,
scientists have discovered that plants also contain substances known as
phytonutrients, or phytochemicals. There are literally thousands of these
chemicals present in cereals, fruits, and vegetables. They have specific roles
to play, such as protecting the plant from strong ultraviolet rays, infections,
and pollution. When people eat fruits, vegetables, grains, and cereals, they may
acquire the benefits of phytonutrients.
vitamin A (beta-carotene is metabolized to vitamin A)
cells to die (apoptosis)
damage caused by smoking and other toxic
carcinogens through the activation of the cytocrome P450 and Phase II enzyme
Certain phytonutrients are believed to help prevent heart
disease. It is likely that some, such as a red pigment called lycopene that
is present in tomatoes, protect blood vessels from cholesterol build-ups on the
artery walls by means of their antioxidant functions. Other plant chemicals may
help to keep blood pressure under control or blood free from clots. Fruit and
vegetable consumption has been linked to decreased risk of stroke -- both
hemorrhagic and ischemic stroke. Each increment of three daily servings of
fruits and vegetables equated to a 22% decrease in risk of stroke, including
transient ischemic attack.
It is possible that some phytonutrients can
provide protection against various types of cancer.
The suspected mechanisms that are involved in this protection are numerous.
Certain phytonutrients, such as bioflavonoids, may block cancer-causing
substances from reaching the tissues and cells that they normally target. They
might, on the other hand, help to prevent blood vessels from reaching a newly
formed cancer and, in effect, starve it to death. Some phytonutrients may work
by triggering enzymes that remove cancer-causing substances from the body, while
others may help to prevent cells that have been exposed to such substances from
becoming malignant and replicating out of control. Certain phytonutrients, such
as chlorophyll, may be capable of protecting the body against cancer simply by
strengthening the immune system so that it can successfully resist invading
cancers; others, such as isoflavones, may block off sites where naturally
occurring body hormones might otherwise attach and trigger cancerous growth. In
the case of soya beans, the phytonutrients thought to play a role in protecting
against breast cancer have been identified as isoflavones, substances that are
very similar in structure to the human hormone oestrogen. Scientists have
yet to prove that phytonutrients protect against particular diseases, but the
evidence suggests that increasing consumption of fruits, vegetables, and other
plant foods is a positive step for health. That this could be life-saving adds
an exciting new dimension. Scientists have been able to relate high intakes of
specific foods in particular countries to low rates of certain diseases. In
countries such as Japan, for example, where soya-based foods such as tofu are
eaten regularly, there are lower rates of breast cancer than
elsewhere. Research has indicated that if Japanese women move to other countries
where their intake of soya products falls, the occurrence of breast cancer among
People in the highest quintile for consumption of spinach or collard greens,
plants high in the carotenoid lutein, had a 46% decrease in risk of age-related
degeneration compared to those in the lowest quintile who consumed these
vegetables less than once per month (Seddon et al. Journal of the American
Medical Association. 1994;272:1413).
HOW MUCH TO EAT
Many specialists recommend that, in order
to ensure a good intake of phytonutrients, a wide vareity of fruits, vegetables,
and cereal products is eaten on a regular basis . In practice, this means trying
to consume at least five servings of fruits and vegetables each day. These can
be fresh or frozen and, in some cases, such as carrots and pulses, canned. Fruit
and vegetable juices count as servings.
EACH SERVING is assumed to weigh about 80g, making a total daily intake of
about 400g of fruits and vegetables. Selecting different colours of fruits and
vegetables is a simple method of ensuring a variety of
CEREALS should be included in most meals if possible.
Wholegrain varieties are the most likely to contain protective phytonutrients
and include wholemeal bread, wholegrain pasta, brown rice, buckwheat, and
bulghur wheat. Wholegrain breakfast cereals also contribute to the dietary
BEANS AND OTHER PULSES are rich in phytonutrients and can be eaten as
an alternative source of protein to meats, fish, and poultry. Using pulses as
the main source of protein once a day will significantly boost phytonutrient
NUTS AND SEEDS supply a range of phytonutrients such as lignans, as
well as many vitamins, minerals, proteins, and essential fats. Some sunflower,
pumpkin, and sesame seeds, as well as a variety of nuts, should be eaten on a
HERBS AND SPICES are good sources of various phytonutrients
and are easy to add to the ingredients in any meal.
Scientists have only recently begun to understand the
contribution that phytonutrients make to human health. Increasing numbers of
these substances are being identified and their properties investigated. The
groups listed below are just a selection of the many phytonutrients that
researchers have analyzed.
These seem to protect against
heart disease and cancer by reducing damage to HDL cholesterol and encouraging
healthy cell growth while discouraging cancerous
Flavonoids may help to fight heart disease by preventing
a build-up of cholesterol on artery walls. They may block cancer-causing
substances and suppress cancerous changes.
oestrogens seem to mimic human oestrogen. They have antioxidant effects and are
thought to help to reduce the risk of heart disease and
These phytonutrients seem to help to neutralize
free radicals and increase the activity of anticancer enzymes. They may reduce
the risk of lung cancer.
These chemicals have weak oestrogenic
effects and appear to limit cancerous changes. They also act as antioxidants and
may help to protect against heart disease.
thought to be able to counteract the effects of pollutants such as cigarette
smoke. They are antioxidants and may help to control cancerous changes to
Saponins seem to help to inhibit tumor formation and aid
fat digestion. They may help to reduce levels of fats in the blood and possibly
reduce the risk of heart disease.
These seem to interfere with
cancer-causing substances, and in particular they may also help to prevent tooth
decay and reduce the risk of stomach cancer.
The following list provides examples of the immense variety of
phytonutrients and their common dietary sources.
BETA CRYPTOXANTHIN: Mangoes, papayas, peaches.
CAROTENOIDS: Carrots, sweet
potatoes, mangoes, apricots.
COUMARINS: Oranges, grapefruits, flax seeds, green
vegetables, green tea.
ELLAGIC ACID: Strawberries, raspberries, blackberries.
FLAVONOIDS: Apples, onions, grapes.
INDOLES: Green leafy
ISOFLAVONES: Soya beans, tofu, soya milk,
ISOTHIOCYANATES: Broccoli and other cruciferous
KAEMPFEROL: Radishes, kale, leeks, endive, broccoli,
LIGNANS: Wholegrains, seeds,
ORGANOSULPHURS: Garlic, onions.
PHENOLIC COMPOUNDS: Citrus fruits,
tomatoes, peppers, tea, wine.
PHYTOENE: Mangoes, pumpkins.
TERPENES: Citrus fruits.
ZEAXANTHIN: Red and yellow peppers.