Effects of low fat diets differing in degree of fat unsaturation on plasma lipids, lipoproteins, and apolipoproteins in adult men.

The effects of two low fat diets with differing ratios of polyunsaturated to saturated fatty acids (P/S) on blood lipids, lipoproteins (LP), and apolipoproteins (Apo) were studied in 23 adult men, 30-60 years old, using a crossover design. Both test diets had 25% fat calories with either a P/S of 0.3 (Diet 1) or a P/S of 1.0 (Diet 2) and equivalent amounts of cholesterol. The study consisted of four periods: a 5-week prestudy on self-selected diet (SS), two 6-week test diet periods followed by a second 5-week post-study period on the SS diet. When compared with the SS diet, Diet 2 lowered the mean plasma total cholesterol (TC) by about 20% (P less than 0.01). Low density lipoprotein (LDL) cholesterol was also decreased by about 18% by Diet 2 (P less than 0.01). The high P/S diet did not cause a change in total cholesterol in the high density lipoprotein (HDL) subclass2 (HDL2) when compared to the SS diet. Levels of triglycerides (TG) were slightly reduced in HDL2 but showed a greater reduction in HDL3 in both diets. Phospholipids (PL) were significantly reduced in HDL2 and in HDL3, but the reduction in HDL3 PL was not statistically significant. Apo A-I levels were not changed by either diet when compared with the SS diet, but Apo A-II levels of HDL2 and HDL3 were significantly decreased by the low fat diets, and there was no P/S effect. No other consistent changes in apoprotein levels occurred. Our data suggest that, in men with normal lipid levels, practical dietary changes involving a moderate increase in P/S from 0.3 to 1.0 in a low fat, low cholesterol diet do influence lipoprotein composition and apoprotein distribution in a short time. The reduction in cholesterol in total lipid composition and in LDL lipids which accompanied the reduction of dietary fat and cholesterol are considered to be beneficial.