Effect of monounsaturated fatty acids on high-density and low-density lipoprotein cholesterol levels and blood pressure in healthy men and women

The purpose of the studies described in this thesis was to examine the effect of monounsaturated fatty acids on the distribution of serum cholesterol over high-density and low-density lipoproteins (HDL and LDL) and on blood pressure in healthy men and women. High levels of LDL cholesterol and blood pressure, and low levels of HDL cholesterol are associated with an increased risk for coronary heart disease.

Three controlled dietary studies were carried out. In the first study it was found that that monounsaturated fatty acids (oleic acid) specifically lowered non-HDL cholesterol when they replaced saturated fatty acids in the diet. In contrast, complex carbohydrates lowered both HDL and LDL cholesterol. The results of the second study indicated that it is immaterial whether saturated fatty acids in the diet are replaced by a mixture of monounsaturated and (n- 6)polyunsaturated fatty acids (oleic and linoleic acid) or by (n-6)polyunsaturated fatty acids alone. The two unsaturated-fat-rich diets had the same effect on HDL cholesterol and both lowered the level of LDL cholesterol to the same extent. In the third experiment we found that, when compared with cis monounsaturated fatty acids, trans monounsaturated fatty acids lower HDL cholesterol levels. In addition, trans fatty acids increased the level of LDL cholesterol, although to a lesser extent than did saturated fatty acids.

No effects of specific fatty acids on blood pressure were detected in any of the three experiments.

It is concluded that replacement of fats rich in saturated or trans fatty acids by oils rich oleic or linoleic acid might be helpful for the prevention of coronary heart disease, as far as lipoprotein levels are concerned. Weight gain, however, might be an unwanted side-effect of such high-oil diets.