Effect of Plant Sterol Esters on the Absorption of Dietary Cholesterol

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Abstract
Cholesterol absorption decreases when either free or esterified plant sterols are added to the dietary fat. The effectiveness of various plant sterols, which were added to the dietary fat at the same molar concentration, in causing this decrease was determined in thoracic duct-cannulated rats. The oleate esters of β-sitosterol, campesterol, and stigmasterol, individually or in a mixture, were all similar in their ability to decrease the absorption of cholesterol from a diet that contained otherwise sterol-free triolein as the only fat. Their effectiveness was equal to that of free β-sitosterol or stigmasterol. β-Sitosterol esters of short (acetate), medium (decanoate), or long (oleate) chain fatty acids did not differ in their ability to lower cholesterol absorption. When the dietary fat contained 1% cholesterol, the addition of twice this amount of plant sterol resulted in a 30% reduction in cholesterol absorption. Increasing the amount of dietary plant sterols resulted in further decreases in the absorption of dietary cholesterol; the response had a log dose relationship. It is proposed that in the intestine, the plant sterol esters are hydrolyzed, and the resulting free sterol decreases the solubility of cholesterol in the oil and micellar phases with a consequent decrease in cholesterol absorption. A similar decrease in the percent absorption of dietary cholesterol ensued, if the level of dietary cholesterol was increased. It is proposed that this was brought about by the same mechanism as that responsible for the effect of the plant sterols. The extensive solubility of the phytosterol esters in fat, in contrast to the limited solubility of their unesterified forms, provides a means for administering effective amounts of these hypocholesterolemic agents.