THE EFFECT OF DIETARY-FAT LEVEL AND QUALITY ON PLASMA-LIPOPROTEIN LIPIDS AND PLASMA FATTY-ACIDS IN NORMOCHOLESTEROLEMIC SUBJECTS

This study examined the effect on the plasma lipids and plasma phospho lipid and cholesteryl ester fatty acids of changing from a typical wes tern diet to a very low fat (VLF) vegetarian diet containing one egg/d ay. The effect of the addition of saturated, monounsaturated or polyun saturated fat (PUFA) to the VLF diet was also examined. Three groups o f 10 subjects (6 women, 4 men) were fed the VLF diet (10% energy as fa t) for two weeks, and then in the next two weeks the dietary fat in ea ch group was increased by 10% energy/week using butter, olive oil or s afflower oil. The fat replaced dietary carbohydrate. The VLF diet redu ced both the low density Lipoprotein (LDL) and high density lipoprotei n (HDL)-cholesterol levels; addition of the monounsaturated fats and P UFA increased the HDL-cholesterol levels, whereas butter increased the cholesterol levels in both the LDL- and HDL-fractions. The VLF diet l ed to significant reductions in the proportion of linoleic acid (18:2 omega 6) and eicosapentaenoic acid (20:5 omega 3) and to increases in palmitoleic (16:1), eicosatrienoic (20:3 omega 6) and arachidonic acid s (20:4 omega 6) in both phospholipids and cholesteryl, esters. Additi on of butter reversed the changes seen on the VLF diet, with the excep tion of 16:1, which remained elevated. Addition of olive oil resulted in a significant rise in the proportion of 18:1 and significant decrea ses in all omega 3 PUFA except 22:6 compared with the usual diet. The addition of safflower oil resulted in significant increases in 18:2 an d 20:4 omega 6 and significant decreases in 18:1, 20:5 omega 3 and 22: 5 omega 3. These results indicate that the reduction of saturated fat content of the diet (<6% dietary energy), either by reducing the total fat content of the diet or by exchanging saturated fat with unsaturat ed fat, reduced the total plasma cholesterol levels by approximately 1 2% in normocholesterolemic subjects. Although the VLF vegetarian diet reduced both LDL- and HDL-cholesterol levels, the long-term effects of VLF diets are unlikely to be deleterious since populations which habi tually consume these diets have low rates of coronary heart disease. T he addition of safflower oil or olive oil to a VLF diet produced favor able changes in the Lipoprotein lipid profile compared with the additi on of butter. The VLF diets and diets rich in butter, olive oil or saf flower oil had different effects on the 20 carbon eicosanoid precursor fatty acids in the plasma. This suggests that advice on plasma lipid lowering should also take into account the effect of the diet on the f atty acid profile of the plasma lipids.