Phytosterols occur naturally in the non-saponifiable material of plant oils. Sitostanol, the saturated derivative of beta-sitosterol, is found in negligible concentrations in plant sources and, hence, is almost absent from typical Western diets. Tall oil extracts, on the other hand, contain about 20% (w/w) sitostanol. Phytosterols have been shown to lower plasma total cholesterol levels in animals and humans while sitostanol exhibited stronger reducing effects. Several studies have suggested that phytosterols lower plasma total cholesterol levels by either inhibiting cholesterol absorption or altering the activities of enzymes critical in cholesterol metabolism and excretion. However, results obtained demonstrate inconsistency regarding the effects of phytosterols on cholesterol absorption rates and cholesterogenesis. In addition, few studies have determined quantitatively the changes in the rate of cholesterol absorption and biosynthesis. Hence, the objective of this thesis was to investigate further the impact of different sources of phytosterols on plasma lipid profiles and to develop a new methodology for simultaneous measurement of percent cholesterol absorption and cholesterol synthesis rates in animals and humans. The stable isotopes, 13C-, 18 O-cholesterol, and deuterium oxide were utilized for the dual isotope plasma ratio and deuterium uptake methodologies. Results from the series of animal experiments conducted demonstrate (i) a gender effect of phytosterols in modulating plasma lipid profile in hamsters, (ii) that sitostanol was more potent in lowering plasma and hepatic lipid concentrations than beta-sitosterol in hamsters and rabbits and (iii) that this lowering effect was due to a reduction in fractional cholesterol absorption and an increase in cholesterol excretion rates. Concomitantly, an up-regulation in cholesterogenesis was observed in hamsters. Furthermore, in humans tall oil phytosterols lowered total cholesterol levels in hypercholesterole
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.35029 |
| Date | January 1998 |
| Creators | Ntanios, Fady Y. |
| Contributors | Jones, Peter (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (School of Dietetics and Human Nutrition.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001610658, proquestno: NQ44534, Theses scanned by UMI/ProQuest. |
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