Comparative effects of polyunsaturated- to saturated fatty acid ratio versus polyunsaturated- and monounsaturated fatty acids to saturated fatty acidratio on lipid metabolism in rats

This study examined the effects of various polyunsaturated fatty acid (PUFA , P)/saturated fatty acid (SFA, S) ratio versus PUFA + monounsaturated fatt y acid (MUFA, M)/SFA ratio on lipid metabolism. The P/S ratio of dietary fa t was fixed at a certain level (0.5, 1, 2, or 4, respectively) for each of four pairs of rat groups respectively, and then the P + M/S ratio was chang ed for the four pairs of rat groups. When the P/S ratio was fixed at 0.5, 1 , 2, or 4, the plasma total cholesterol, LDL-cholesterol (C), and HDL-C lev els did not show any significant difference in each pair of groups with dif ferent P + M/S ratios. However, when the P/S ratio was fixed at 1.0, the hi gher P + M/S ratio of 5.7 (M/S = 4.7, P/M = 0.2) resulted in significantly higher plasma total triacylglycerol (TAG), VLDL-TAG, VLDL-C, and VLDL-phosp holipid (PL) than the lower P + M/S ratio of 1.4 (M/S = 0.4, P/M = 2.4). Wh ereas when SFA was fixed at a similar level, it therefore had approximately the same P + M/S ratio(5.3, 5.6, 5.7), and by increasing the P/S ratio fro m 1, 2 to 4 (70.4, 52.7 and 23.2% of the total fatty acids as MUFA respecti vely), the plasma VLDL-C, VLDL-TAG, and VLDL-PL concentrations decreased pr ogressively. When PUFA or MUFA was kept on a similar level (14.9 or 53% res pectively), the higher P + M/S ratio (5.7 or 5.3, respectively) resulted in significantly greater accumulation of liver cholesterol than the lower P M/S ratio of 2.2. When the P/S ratio was fixed at 1 or 4, the diet of high er P + M/S ratio in a pair of the groups also resulted in greater accumulat ion of liver cholesterol. The results of the study suggests that if the P M/S ratio was below 3, the change in the P/S ratios (0.5, 1 or 2) did not affect the levels of plasma total and lipoprotein cholesterol and TAG. Incr eases in the plasma VLDL-C and VLDL-TAG were related to increased MUFA cont ent in the diet. And high MUFA content resulted in greater accumulation of liver cholesterol. It seems that the prerequisites for keeping low plasma a nd liver cholesterol are (a) low M/S ratio and (b) high PIM ratio and (c) P + M/S ratio not to exceed 3. (C) 1999 Elsevier Science Ireland Ltd. All ri ghts reserved.