are several types of fats, the chief ones being called triglycerides,
cholesterol esters, and phospholipids. They contain fatty acids, which
may be saturated, monounsaturated or polyunsaturated.
polyunsaturated fatty acids are essential for humans because they cannot
be made in our bodies. One group of essential fatty acids comes from
plant sources; these fatty acids are found in considerable quantity
in polyunsaturated margarine and in vegetable oils. We need about 1
to 2 per cent of our energy to come from this type of fatty acid, although
a higher intake, up to about 10 per cent of energy, may be protective
against coronary heart disease. The requirements of another type of
essential fatty acid have not been worked out, but they are obtained
mainly from seafood and, in a different way, seem protective against
coronary heart disease - they reduce the 'stickiness' of the blood.
Both kinds of essential fatty acids can lower high levels of blood fats.
acids come chiefly from ruminant animals, such as sheep and cattle,
and from milk and dairy products of these animals. In the stomachs of
ruminants the polyunsaturated fatty acids that are present in fodder
are broken down to a large extent to saturated fatty acids so that the
fatty tissues of animals such as cattle are mostly saturated. On the
other hand, animals with a single stomach (monogastric) absorb the range
of fatty acids, saturated and polyunsaturated, present in the diet.
Pigs and humans are similar in this respect. Furthermore, domesticated
animals have more carcass fat than wild animals so that the advent of
animal production for human consumption has led to a great increase
in the consumption of saturated fat.
Saturated fat increases
the amount of cholesterol in blood. Monounsaturated fat does not increase
the blood cholesterol level and may decrease it (olive oil and peanut
oil provide monounsaturated fat). Polyunsaturated fat decreases it.
Traditional cultures that use olive oil in food preparation or a lot
of groundnuts (peanuts) have little coronary heart disease. Cholesterol
in food increases the level of cholesterol in blood.
Saturated fat also
increases the amount of triglyceride in the blood. Both blood cholesterol
and blood triglyceride, when elevated, increase the risk of hardening
of the arteries (atherosclerosis), with consequent coronary heart disease.
ratio of polyunsaturated to saturated fat in the diet is:
: 1 (i.e. 50 : 50).
Some novel food
products have been developed to decrease the saturated and increase
the polyunsaturated fat of the total diet. Foods traditionally high
in saturated fat, such as icecream made with milkfat, are now available
made from polyunsaturated vegetable oils.
Dairy and beef
cattle have been fed polyunsaturated fat protected from digestive breakdown
so that the dairy and beef products are more polyunsaturated. Eggs have
also had the yolk, rich in cholesterol, removed and replaced with a
polyunsaturated oil substitute -- hence 'polyunsaturated egg mix', with
the main advantage being a low cholesterol content.