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