Journal Name:
Metabolism: Clinical and Experimental
Article Title:
Fat-modified diets influence serum concentrations of cholesterol precursors and plant sterols in hypercholesterolemic subjects.
Date Written:
1998
Volume:
47
Number:
6
Page:
744
Author(s):
Sarkkinen, E.S.; Uusitupa, M I.; Gylling, H.; Miettinen, T.A.
Article:
Serum noncholesterol sterols have been used to study cholesterol absorption and synthesis. Cholesterol precursor sterols in serum are reflective of cholesterol synthesis, while serum plant sterols (campesterol and sitostanol) are indicative of absorption and biliary elimination of sterols. Further, serum concentrations of plant sterols exhibit positive correlations with the polyunsaturated (PUFA) to saturated fatty acid (SFA) ratio of dietary fat and with the proportion of linoleic acid (LA, omega 6) in serum and dietary lipids). Previous research by this group showed that the enrichment of the diet with sunflower oil (SO) or rapeseed oil (canola oil - RO) significantly decreased serum low-density lipoprotein (LDL) cholesterol concentrations. The mechanisms proposed for this effect include altered fatty acid composition as well as changes in cholesterol metabolism. The objectives of the present study were to examine the proportion of serum cholesterol precursors and plant sterols following four different fat-modified diets: high-fat, saturated fat-enriched (control), reduced-fat, SO-enriched (SO-enriched), RO-enriched (RO-enriched), and reduced-fat, saturated fat-enriched (reduced-fat). In addition, the relationship of serum plant sterols with the proportion of unsaturated fatty acids in dietary and serum lipids was assessed.
Diets were fed for 6 months to 160 hypercholesterolemic subjects in a parallel design. The proportion of lathosterol (micrograms per 100 mg cholesterol), a precursor of cholesterol synthesis, increased significantly following both SO-enriched (mean +/- SD 147 +/- 57 vs. 167 +/-76) and RO-enriched (147 ± 54 vs. 157 +/- 52) groups, where the reduction in low-density lipoprotein (LDL) cholesterol was also significant. The proportion of sitosterol, a plant sterol, decreased significantly in the control group (137 ± 48 vs. 122 ± 42), and the proportion of campesterol, increased in the RO-enriched group (280 ± 141 vs. 333 ±162), reflective of the vegetable oils used in these two groups rather than increased cholesterol absorption. In the whole study population, the proportion of LA and omega 3 alpha-Iinolenic acid in cholesterol esters (CEs) was significantly correlated with the proportion of sitosterol and campesterol in serum at the end of the study.
In both groups on diets enriched with either SO or RO, the proportion of lathosterol, which is related negatively to both the fractional and absolute absorption of cholesterol but positively to overall cholesterol synthesis, increased significantly. This could reflect an enhanced endogenous cholesterol synthesis during these two diets as a feedback mechanism to reduced cholesterol absorption, resulting in a diminished hepatic cholesterol concentration. Additionally, this may have activated the LDL apo B receptor activity, ultimately resulting in a decrease in total and LDL cholesterol. Dietary sterols also appear to compete for absorption during digestion. In the present study, the proportion of SFA was markedly reduced during both vegetable oil-enriched diets, which might also have affected cholesterol absorption at least to some extent.
During the present study, the only change in the serum concentration of plant sterols was a marked increase in the campesterol concentration of the RO-enriched group and a reduction of sitosterol in the control group. Plant sterols correlate positively with cholesterol absorption, but they correlate with the dietary unsaturated to saturated fatty acid ratio, as well, probably due to a high plant sterol content in vegetable oils. As the amount of campesterol in RO is markedly higher than in other vegetable oils, the authors postulated that the increased concentration of campesterol cannot be considered a marker of increased cholesterol absorption, but rather an indicator of the use of this particular campesterol-rich vegetable oil. The altered plant sterol intake most likely also reduced the proportion of cholesterol in the control and RO-enriched diet groups significantly and in the SO-enriched group non significantly.
The authors concluded that the increase in the concentration of lathosterol found in both RO- and SO-enriched diets could indicate that the significant reduction in the LDL cholesterol concentration seen may be due to cholesterol malabsorption with a compensatory increase in cholesterol synthesis, in addition to the changes induced by dietary fatty acid composition. The increases in the concentration of plant sterols (campesterol and sitosterol) indicate the use of vegetable oils and an increased plant sterol intake, rather than increased cholesterol absorption, in hypercholesterolemic subjects.
Back to New research paper