Journal Name:
Arteroisclerosis and Thrombosis
Article Title:
Effect of dietary fat selection on plasma cholesterol synthesis in older, moderately hypercholesterolemic humans
Date Written:
1994
Volume:
14
Number:
Page:
542
Author(s):
Jones, P.; Lichtenstein, A.; Schaefer, E.; Namchuk, G.
Article:
The association between elevated plasma cholesterol levels and risk of coronary heart disease (CHD) in humans has been well established. Research has also determined that dietary intake of saturated fatty acids (SFA) increases plasma cholesterol levels, while intake of mono - and - polyunsaturated fatty acids (PUFA) results in a hypcholesterolemic effect. However, the actual mechanism by which dietary fats influence circulating cholesterol levels remains unclear. The objective of this study was two-fold: first, to examine the influence of the ratio of monounsaturated fatty acids (MUFA) to PUFA on circulating cholesterol levels and plasma cholesterol synthesis rates in moderately hypercholesterolemic subjects; and second, to examine the effect of fatty acid and plant sterol content of different plant based oils (corn, olive, canola) on plasma cholesterol synthesis rate in these same subjects.
Fifteen hypercholesterolemic subjects (LDL-C levels >130 mg/dl) participated in this randomized double-blind study. Participants consumed four experimental diets for a 32-day period, each separated by a 7-14 day washout period. A baseline diet was initially consumed for 32 days, consisting of 16.5% calories from protein, 35.4% calories from fat (15% SFA, 15% MUFA, 6% PUFA), and cholesterol content of 128mg/1000kcal per day. Three experimental diets consistent with National Cholesterol Education Program guidelines containing 30% of kcal as fat, with two-thirds of fat derived from either olive, corn, or canola oil, and a daily cholesterol intake of 80 - 85mg/1000 kcal were consumed by each participant in a random order and double-blind fashion. PUFA to SFA ratios for the diets were: baseline = 0.616, olive oil = 0.558, corn oil = 1.652, and canola oil = 1.239. Fasting blood samples were obtained at baseline and during the final week of each dietary phase and used for subsequent analysis of plasma total, LDL-c, HDL-c, and triglyceride (TG) concentrations. Cholesterol fractional synthesis rate (FSR) was also measured as deuterium (D) incorporation into cholesterol. Absolute synthesis rates (ASRs) were also calculated as the product of FSR and rapid turnover cholesterol pool size.
Results demonstrated a significant decline in total cholesterol levels in subjects consuming the olive oil (205 +/- 5 mg/dL), corn oil (194 +/- 5 mg/dL), and canola oil (194 +/- 5 mg/dL) diets when compared to the baseline diet (221 +/- 8 mg/dL). No significant difference in TG levels was observed between any of the diets. LDL-C levels were lower during consumption of the olive oil (132 +/- 5 mg/dL), corn (125 +/- 5 mg/dL), and canola oil (126 +/- 5 mg/dL) when compared to the baseline diet (152 +/- 8 mg/dL). HDL-C levels were reduced following the corn and canola oil diets when compared to baseline, while the olive oil diet produced no significant change. FSR rates were higher for the corn oil (0.0665 +/- 0.0097 pool/d) and olive oil (0.0409 +/- 0.0052 pool/d) diets, but not the canola oil diet (0.0492 +/- 0.0072 pool/d) when compared to baseline (0.0412 +/- 0.0060 pool/d ). Mean elevated ASR values were observed for both the corn oil and olive oil diets, but not for the canola oil diet.
These findings suggest reduced serum cholesterol levels following plant oil consumption may be due in part to enhanced cholesterol synthesis in humans. The fatty acid or plant sterol levels of the dietary oils consumed may play a role in the regulation of cholesterogenesis. Plant sterols or other components found in the plant oils appear to up-regulate cholesterogenesis indirectly by depressing the absorption of cholesterol, or directly by serving as a cholesterolgenic precursor, overall resulting in more rapid cholesterol clearance. The data supports the lipid lowering effects of both a healthy fatty acid profile such as that found in canola oil as well as a favorable sterol composition. Plant sterols compete with dietary cholesterol for absorption and thus limit the amount of cholesterol available in the bloodstream.,
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