Journal Name:
Metabolism
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.; Uusitupa, M.; Gylling, H.; Miettinen, T.
Article:
Serum noncholesterol sterols, cholesterol precursors and plant sterols have been recently used as indicators of cholesterol absorption and synthesis. Cholesterol precursor sterols in serum including desmosterol, lathosterol, and squalene, can indicate cholesterol synthesis. Plant sterols are found in differing amounts in vegetable oils and dietary levels are related to serum levels. The concentrations of serum plant sterols such as campesterol and sitosterol correlate positively with cholesterol absorption and have also been found to correlate with dietary PUFA to SFA ratios. Previous research by the authors indicated that sunflower oil (SO) or CO (low erucic acid rapeseed) significantly decreased serum LDL-C in hypercholesterolemic subjects. The contribution of altered cholesterol metabolism to the reduction in LDL-C was not reported. In this study, the proportion of serum cholesterol precursors and plant sterols during four fat-modified diets and the relationship of serum plant sterols to serum lipid levels were assessed.
One hundred and sixty free-living hypercholesterolemic subjects consumed one of four diets for 6 months. The control diet (n=36) consisted of 35% fat comprised of 14.5% SFA, 10.0% MUFA (including 4.4% OA) and 3.6% PUFA (including 2.5% LA). The reduced fat diet (n=39) consisted of 30% fat comprised of 11.8% SFA, 8.2% MUFA (including 2.7% OA) and 3.2% PUFA (including 2.1% LA). The SO diet (n=37) consisted of 32% fat comprised of 10.2% SFA, 8% MUFA (including 4.4% OA) and 8% PUFA (including 7% LA). The CO diet (n=41) consisted of 34% fat comprised of 10.6% SFA, 11.3% MUFA (including 7.5% OA) and 5.4% PUFA (including 3.7% LA). The diets were fed in a parallel design. Serum lipids, cholesterol precursors and plant sterols were measured at 2 weeks, 6 weeks, 3 months and 6 months.
Serum LDL-C levels were decreased to a similar and significant extent by both the SO and CO diets. Serum TC and HDL-C increased slightly following the control diet, while HDL-C remained unchanged with the other diets. The proportion of ALA in cholesterol esters (CE) increased significantly following both the control and CO diet, reflecting the levels of ALA in the CO products used. LA increased in CE as well in both the CO and SO groups. The proportion of lathosterol, a precursor of cholesterol synthesis, increased significantly in both the SO and CO groups. The authors postulated that the increase in lathosterol may indicate that the observed LDL-C reductions could be due to cholesterol malabsorption leading to compensatory enhanced cholesterol synthesis.
The proportion of the plant sterol sitosterol decreased significantly in the control group while campesterol levels increased in the CO group. The amount of campsterol in CO is higher than in other vegetable oils. The authors attributed modified serum plant sterol levels to the differing dietary vegetable oil intakes between the two diets rather than increased cholesterol absorption. Previous studies have reported that cholesterol absorption efficiency may be reduced following a CO-enriched diet. This may be due to an increased intake of plant sterols from CO, which have been found to compete with cholesterol for absorption. Reduced cholesterol absorption may have contributed to lower LDL-C levels.
In the whole study population, the proportion of LA and ALA in CE was positively correlated with the proportion of sitosterol (r = .43) and campesterol (r = .36) in serum at the end of the study. No changes in cholesterol precursors were found in the control or reduced fat diets in which serum cholesterol levels remained unchanged. The authors concluded that serum cholesterol precursors appear to be useful indicators of cholesterol metabolism. Changes in serum plant sterol levels were found to reflect dietary changes rather than cholesterol metabolism during long term dietary intervention with the fat-modified diets., , , ,
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