To study the effects of dietary phytosterols on plasma cholesterol, Wistar rats were fed diets containing a cholesterol overload (24 mg/day), to which phytosterols were added or not (24 or 96 mg/day). The cholesterol overload led to a marked increase in cholesterol, mainly linked to very-low-density and low-density lipoproteins. Phytosterols reduced those effects, the highest dose being most efficient. No undesirable effect was observed either on body or on liver weights. This shows that low doses of phytosterols are sufficient to significantly decrease a plasma cholesterol enhancement induced by a dietary cholesterol overload.
To study the effects of dietary stigmasterol on sterol and bile acids metabolism, Wistar rats were fed diets containing various amounts of stigmasterol. Feeding high stigmasterol doses (11, 26 or 52 mg/day) led to increased cholesterol, coprostanol and bile acid output. These effects were dose-dependent, and likely to be related to the inhibitory effect of plant sterols on cholesterol absorption. Moreover, it accounts for the beneficial effect of the stigmasterol on cholesterol lowering.
The effects of dietary phytosterols on lipid metabolism have been assessed through determination of liver lipids (sterols and fatty acids) and lipid metabolism enzymes (acetyl-CoA carboxylase, malic enzyme, glucose-6-phosphate dehydrogenase) in rats fed 12 or 24 mg cholesterol a day and 0-96 mg phytosterols. The results indicate that, provided the dietary phytosterol to cholesterol ratio is at least 1 and in the presence of a dietary cholesterol excess, phytosterols do exert a regulatory role through decreases of both acetyl-CoA carboxylase and malic enzyme activities. A ratio of 2 enhances this effect. At the same time, liver fatty acids and cholesterol contents significantly decrease.
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