Dietary Phytosterols Inhibit the Lipid Modulating Effects of Sesamin in Rats

The major lignan in the unsaponifiable fraction of sesame lipids, sesamin, is known to affect lipid metabolism. For example, sesamin inhibits the clearance of tocopherols, the activity of Δ5-desaturase during fatty acid metabolism, and reduces cholesterol absorption and biosynthesis. In order to study whether dietary phytosterols, which are known to reduce the absorption of lipid soluble dietary factors, may influence the lipid-modulating effects of sesamin, rats were fed, in a 2×2 Latin-square design, diets containing two concentrations of sesamin and phytosterols for 4 weeks. Tocopherols and cholesterol were analyzed in plasma and liver and the fatty acid profile was determined in liver lipids. Sesamin increased α-tocopherol concentrations in plasma and liver (p<0.001), whereas the phytosterols had no effect. However, an increase in the phytosterol content of the diet resulted in a reduction of the α-tocopherol-elevating effect of sesamin in plasma (p<0.01). Similarly, sesamin increased the percentage of dihomo-γ-linolenic acid in liver lipids (p<0.05), which was abolished by the addition of phytosterols. Neither sesamin nor phytosterols significantly altered cholesterol concentrations in plasma or liver. In conclusion, these results suggest that in rats, dietary phytosterols may interact with sesamin in a way reducing its biological activities.