Journal of Lipid Research, Vol. 9, 374-387, May 1968
Copyright © 1968 by Lipid Research, Inc.

Dietary ßbeta;-sitosterol as an internal standard to correct for cholesterol losses in sterol balance studies

Scott M. Grundy , E. H. Ahrens Jr. , and G. Salen

The Rockefeller University, New York 10021

In the course of carrying out sterol balance studies in 19 patients, we gathered the following evidence that, in some but not all patients, considerable amounts of neutral sterols are "lost" during their passage through the intestinal tract. (a) Since plant sterols are largely nonabsorbable in man, they should be totally recovered in the feces; yet in many patients significantly less plant sterol than expected was recovered, the loss amounting to as much as 56% of daily intake. (b) In two patients in whom cholesterol-¹⁴C and ßbeta;-sitosterol-³H were instilled into the terminal ileum, from which neither sterol is absorbed, the feces contained 25% less of each isotope than was instilled. (c) In four patients fed radioactive cholesterol daily until the isotopic steady state was closely approximated, 28-50% of the isotope could not be accounted for. On the other hand, in five patients fed radioactive bile acids until the isotopic steady state was approximated, input equalled output as predicted.

Since the amount of ßbeta;-sitosterol absorbed in man is limited (5% or less), this sterol can be used as an internal standard for upward correction of the figure obtained for the amount of neutral steroids excreted. The use of ßbeta;-sitosterol for this purpose is based on three considerations: (a) it passes through the intestine in the same physicochemical state as cholesterol; (b) it accompanies cholesterol at every step of its isolation and chromatographic measurement; and (c) it is lost to the same extent as cholesterol. Excretion data for fecal neutral steroids can therefore be corrected for irregular fecal flow as well as for the "unexpected loss" referred to.

This loss seems to be due not to errors in stool collection or to technical errors, but to intestinal bacterial degradation of neutral 3ßbeta;-OH,⁵-sterols to products not recognized as steroids in the analytical methods used.

Supplementary key words cholesterol • cholesteryl sulfate • ßbeta;-sitosterol • plant sterols • degradation • internal standards • cholesterol balance • isotopic steady state • chromic oxide

Submitted on December 16, 1967
Accepted on February 21, 1968

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