Metabolism of β-sitosterol in man

Abstract

A C T The metabolism of P-sitosterol was com- pared to that of cholesterol in 12 patients.Sterol bal- ance methods were supplemented by radiosterol studies, with the following results.(a) Plasma concentrations of P-sitosterol ranged from 0.30 to 1.02 mg/100 ml plasma in patients on intakes of 6-sitosterol typical of the American diet.Plasma levels were raised little when intakes were increased greatly, and on fixed intakes they were constant from week to week.On diets devoid of plant sterols, the plasma and feces rapidly be- came free of p-sitosterol.(b) The percentage of esterified P-sitosterol in the plasma was the same as for cholesterol.However, the rate of esterification of P-sitosterol was slower than that for cholesterol.(c) Specific activitytime curves after simultaneous pulse labeling with #-sitosterol-3H and cholesterol-"C conformed to two- pool models.The two exponential half-lives of f-sitosterol were much shorter than for cholesterol, and pool sizes were much smaller.Values of turnover for ,8-sitosterol obtained by the sterol balance method agreed closely with those derived by use of the two-pool model.There was no endogenous synthesis of P-sitosterol in the patients studied; hence, daily turnover of P-sitosterol equaled its daily absorption.Absorption of P-sitosterol was 5% (or less) of daily intake, while cholesterol ab- sorption ranged from 45 to 54% of intake.(d) About 20% of the absorbed f-sitosterol was converted to cholic and chenodeoxycholic acids.The remainder was ex- creted in bile as free sterol; this excretion was more rapid than that of cholesterol.(e) The employment of i3-sitosterol as an internal standard to correct for losses of cholesterol in sterol balance studies is further vali- dated by the results presented here.course of these studies we obtained other data concern- ing the metabolism of 3-sitosterol in man, such as the question of its endogenous synthesis (13), its esterifica- tion and transport in the plasma, and its transformation into cholic and chenodeoxycholic acids. METHODS PatientsStudies were carried out on the metabolic ward at The Rockefeller University Hospital; the age, sex, body build, and clinical diagnosis of each patient are given in Table I.Eight patients had familial hypercholesterolemia with normal 952