The notion that
'natural' food may be harmful is not widely appreciated. The terms
'health', ‘organic', 'natural', 'unprocessed', 'no added chemicals'
when applied to food suggest that the food is safe or more nutritious
than its conventional counterpart but this is not necessarily true.
All food is made up entirely of chemicals. In addition to well-known
nutrients such as carbohydrate, fat, protein and water, food contains
many other substances, often in very small amounts.
in food may have a degree of toxicity or 'poisonousness', whether
it is natural, deliberately added, or a contaminant. There is nothing
special about natural chemicals in food and no distinction should
be made between natural and other substances when deciding if a food
is likely to be hazardous. For example, a potato contains a number
of poisonous substances such as nitrate, arsenic and solanine but
in the amounts in which potatoes are normally eaten these natural
substances are not hazardous. For this reason it is important not
to consume large amounts of a small number of foods, as in some faddist
diets, but to consume a wide variety of foods. This not only minimizes
the amount of a particular potentially hazardous substance but also
ensures that a range of essential nutrients are consumed.
29 lists a number of substances that occur naturally in
food and have either caused illness or are suspected of being hazardous
to health. Usually these effects have occurred only when excessive
amounts of a food containing these substances have been eaten. In
fact, for most of us there is little hazard from these foods. The
concentration of these poisonous substances is so low in the food
we eat that we would have to consume huge amounts over a long time
for the toxic effect to show up. Nevertheless, it is import ant to
realize that there are many potentially hazardous substances in our
diet without any obvious effects on our health, and that this applies
equally to 'natural' and processed foods. Natural foods can be harmful
if they are contaminated with excessive amounts of environmental contaminants,
or aflatoxin or other mycotoxins produced by some moulds.
Herbal teas have
become popular with an increasing number of people. Herbal and 'bush'
teas contain a large number of different components, many of which
have not yet been assessed for safety. Some teas can lead to disturbing
effects. Tea made from the South Pacific kava plant has been associated
with impaired breathing, vision and hearing, and other symptoms. Comfrey
and tea made from the roots of sassafras contain substances that have
caused cancer in laboratory animals. In addition, some teas can interfere
with the therapeutic value of some drugs that are taken at the same
time. The heavy consumption of these teas is not to be recommended.
Tea, coffee and cola-type drinks contain caffeine
(about 30, 40, and 10 milligrams per 100 millilitres respectively).
Although individuals react differently to caffeine, the heavy consumption
of these drinks can cause, in addition to stimulation, nervousness,
increased urination, upset stomach and irritability (Chart