Impact of hydrogenated fat consumption on endogenous cholesterol synthesis and susceptibility of low-density lipoprotein to oxidation in moderately hypercholesterolemic individuals

The effects of replacing corn oil with corn oil margarine in stick form on endogenous cholesterol synthesis and susceptibility of low density lipoprotein (LDL) to oxidation were assessed in 14 middle-aged and elderly men and women aged 63 +/- 12 years (mean +/- SD) with moderate hypercholesterolemia (mean LDL-cholesterol [LDL-C], 4.24 +/- 0.59 mmol/L at the time of recruitment). Subjects consumed each of two diets for 32 day periods, one enriched in corn oil, which contained 30% of energy as fat (7% saturated fatty acid [SFA], 9% monounsaturated fatty acid [MUFA] [0.4% 18:1n9 trans], and 11% polyunsaturated fatty acid [PUFA]) and 85 mg cholesterol/4.2 MJ, and one enriched in stick corn oil margarine, which contained 30% fat (8% SFA, 12% MUFA [4.2% 18:1n9 trans], and 8% PUFA) and 77 mg cholesterol/4.2 MJ. Both diets were isocaloric and supplied by a metabolic research kitchen. Mean total cholesterol levels were lowest (P = .039) when subjects consumed the corn oil-enriched diet (5.01 +/- 0.51 mmol/L) as compared with the margarine enriched diet (5.30 +/- 0.58 mmol/L). LDL-C levels were 3.24 +/- 0.51 and 3.50 +/- 0.54 mmol/L when subjects consumed corn oil- and margarine-enriched diets, respectively (P = .058). There were no significant differences in high-density lipoprotein cholesterol (HDL-C) or triglyceride concentrations between the two experimental periods. Consumption of the margarine enriched diet versus the corn oil-enriched diet tended to result in lower cholesterol fractional synthetic rates ([C-FSRs] 0.0466 +/- 0.0175 and 0.0668 +/- 0.0298, respectively, P = .080) and cholesterol absolute synthetic rates ([C-ASRs] 1.1761 +/- 0.5375 and 1.6954 +/- 0.8685, respectively, P = .092); however, differences did not reach statistical significance. Consumption of the margarine enriched diet versus the corn oil-enriched diet resulted in a significantly higher concentration of alpha-tocopherol in both plasma and LDL (P = .004 and P = .011, respectively). LDL particle size tended to be smaller after subjects consumed the margarine enriched diet versus the corn oil-enriched diet (P = .103). Susceptibility of LDL to oxidation was similar after consumption of the corn oil- and margarine-enriched diets. These data Suggest that an increased rate of endogenous cholesterol synthesis did not contribute to the higher plasma cholesterol concentrations during the period when subjects consumed the margarine enriched diet. Therefore, the increase in cholesterol concentration resulting from margarine consumption was likely attributable, at least in part, to a decreased catabolic rate of cholesterol. Additionally, susceptibility of LDL to in vitro oxidation was not altered by consumption of hydrogenated fat. (C) 1996 by W.B. Saunders Company