Dr Ryde's Casebook - July 1998
Nutritionists advise us to reduce the amount of fat in our diet. However, I've
heard that some fats are "essential". Which are they, what foods do
we obtain them from, and how much do we need?
In the western diet, approximately
40% of calories derive from fat, 40% from carbohydrate and 20% from protein. In
rural areas of developing countries the corresponding figures are 10%, 80% and
10% respectively. This massive contrast in dietary patterns, together with smoking
and lack of exercise, plays a significant part in the development of degenerative
diseases. Much of the fat consumed in the western diet is saturated fat of animal
origin, compared with the smaller quantities of mainly unsaturated fats from the
plant foods which make up the bulk of the diet in poorer countries.
The meat
of domesticated animals is generally rich in cholesterol and saturated fat which
further stimulates cholesterol production. In contrast, plant foods contain little
or no cholesterol and are generally low in saturated fat. Thus, although Chinese
peasants typically consume 25% more calories per kilogram of body weight than
their western counterparts, they are very rarely obese. However, within a generation
of emigrating to an affluent western nation, such people are often overweight
and beginning to suffer from degenerative conditions such as heart disease, diabetes,
stroke, hypertension and certain cancers. Mediterranean peoples consume healthier
fats than North Europeans, but they still consume too much fat, leading to obesity
in later life. However, their largely plant-based diet, rather than their fat
intake, may explain their lower incidence of heart disease.
Our bodies convert
excess calories into fat, but there are two unsaturated fats which are called
"essential fats" because they must be present in the diet. These fats,
or oils as they are liquid at room temperature, are the omega 3 and omega 6 fatty
acids, and they are found mainly in green leafy vegetables, nuts and seeds, and
fish. The essential fatty acids (EFAs) are important for growth, fertility, kidney
function and immunity, and for a healthy heart, arteries, joints and skin. Only
modest amounts of extra virgin plant oils should be used in the kitchen, the remaining
EFAs being obtained from eating nuts, seeds and fresh green leafy vegetables.
Though modest amounts of essential oils are beneficial an excess may be harmful,
giving rise to diabetes and blood clotting defects for example. They are best
obtained from a variety of plant foods rather than from fish which is rich in
cholesterol and an increasing source of chemical residues, especially farmed fish.
Ground raw linseed (flaxseed) is an excellent source of omega 3 oil (use an electric
coffee grinder or mortar and pestle to crush the seeds). Two tablespoons a day
can reduce blood cholesterol levels and makes an excellent laxative. Sunflower
seeds are a good source of omega 6 oils.
Dr David Ryde