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We analyzed the effects of different types of dietary fat on the lecithin-cholesterol acyltransferase (LCAT) activity in 20 healthy women aged 26–49 years, consuming 6-week diets containing 54% of the calories as carbohydrates, 16% as protein and 30% as fat. The tested fats were successively: low erucic acid rapeseed (LEAR oil), sunflower oil, peanut oil and milk fats (butter and cream). The fractional and molar rates of LCAT were higher after sunflower and peanut oil diets and decreased significantly after LEAR oil and milk fat diets. The LCAT activity was independent of the P/S ratio of the diet, but positively correlated with the percentage of linoleic acid in serum phospholipids and cholesteryl esters, and negatively correlated with the percentage of oleic acid in the same fractions. Our results showed no relation between LCAT activity and the concentration of plasma cholesterol or triglycerides, no change in serum cholesteryl ester/total cholesterol ratio and confirmed that the distribution of high density lipoprotein subfractions is due to prerequisites other than LCAT.

The effects of 3 dietary fats (olive oil, canbra oil and butter) on the fatty acids of blood lipids and on serum lipoproteins were compared in 6 healthy adult outpatients, after a 6-day normocaloric diet including 35% of the studied fat. Important, although incomplete, changes appeared in the fatty acid composition of the various serum lipids and in the composition and distribution of serum lipoproteins. These changes probably result from the degree of saturation of the fat ingested. Moreover, differences were observed among individual subjects. Genetic differences, which are important in clinical practice, are stressed in connection with risks of vascular diseases and hyperlipidemia and affect intestinal fat absorption and lipoprotein metabolism.

Seasonal variations of blood lipids, which must be considered when performing long-term studies, could be partially due to dietary changes. In the present study, serum lipid parameters were measured each month for 1 year in nuns living in a monastery, whose diet was perfectly regular and controlled. The serum lipid variations observed consisted mainly of an increase in total cholesterol, low-density lipoproteins and apolipoprotein B in autumn and spring and an increase in high-density lipoprotein cholesterol in winter, whereas apoli-poproteins A-I and A-II showed a marked increase in summer and at the beginning of autumn. These variations were probably induced by factors directly related to seasonal rhythm and not to dietary factors or physical exercise. Lastly, the influence of sex hormones seems to be very minor, as postmenopausal women (one-third of the persons) had an identical variation in their lipid parameters, to that observed in the whole group.

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