BOSTON, MASSACHUSETTS. There is ample evidence that the consumption of hard
(stick) margarine increases the risk of atherosclerosis. It is believed that the offending
components in the margarine are trans-fatty acids formed during the hydrogenation
of vegetable oils to form the solid margarine. Semi-liquid and soft margarines have
recently come on the market and are claimed to be more heart healthy than the solid form.
Researchers at the Center on Aging at Tufts University have just completed a study to
determine how different types of oils and fats affect cholesterol levels. Their study
involved 18 women and 18 men over the age of 50 years who had LDL cholesterol (the
"bad" kind) levels exceeding 130 mg/dL (3.36 mmol/L). The participants were fed six
different diets in random order for 35-day periods. All the diets provided 30 per cent of
calories as fat, but were based on different sources of fat. Diet 1 contained 67 per cent of
its fat content as soybean oil (less than 0.5 g of trans-fatty acid per 100 g of fat); diet 2
contained 67 per cent of its fat content as semi-liquid margarine (less than 0.5 g/100 g);
diet 3 contained soft margarine (7.4 g/100 g); diet 4 contained shortening (9.9 g/100 g);
diet 5 contained stick margarine (20.1 g/100 g); and diet 6 (the control diet) contained 67
per cent of its fat as butter. Cholesterol measurements showed that both total and LDL
cholesterol levels were lowest for the soybean oil and semi-liquid margarine diets followed
by the soft margarine diet, the shortening and stick margarine diets, and finally the butter
diet. HDL cholesterol (the "good" kind) was highest in the butter diet and lowest in the
stick margarine diet. Levels of Lp(a) lipoprotein were lowest with the butter diet and
highest with the stick margarine diet. A high level of Lp(a) lipoprotein has been found to
increase the risk for cardiovascular disease.
The researchers conclude that both the general public and people with high cholesterol
levels should be encouraged to use vegetable oils in their natural state or after minimal
hydrogenation and should avoid shortening and stick margarine. In an accompanying
article researchers at the Harvard Medical School support this conclusion, but point out
that avoiding fats with a high trans-fatty acid may be difficult as there are no
mandatory labeling requirements for them. For example, a doughnut contains 3.2 grams
of trans-fatty acids and a large order of french fries 6.8 grams. The Harvard group
also points out that saturated fatty acids such as found in butter appear to be less harmful
than the trans-fatty acids found in margarines when compared on a per gram
basis.
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