EVALUATION OF THE USE OF BETA-SITOSTANOL AS A NONABSORBABLE MARKER FOR QUANTIFYING CHOLESTEROL ABSORPTION

For over a decade investigators have quantified cholesterol absorption by comparison of dietary intake and fecal excretion of isotopic chole sterol with that of beta-sitosterol as a ''nonabsorbable'' marker. How ever, beta-sitosterol might not be ideal due to its potential for abso rption. We therefore carried out two studies to evaluate a new marker with less potential for absorption, [H-3]beta-sitostanol. In the first study (Study I, n = 22), we compared absorption of [H-3]beta-sitostan ol and [C-14]beta-sitosterol in a simultaneous dual-label continuous f eeding (''phytosterol absorption'') experiment. We observed a consiste ntly higher ratio of [H-3]beta-sitostanol/[C-14]beta-sitosterol in the stool relative to diet on the first day of fecal collection (6.1% +/- 3.2% loss of [H-3]beta-sitosterol, range 3-12%), but thereafter, the ratio in stool was similar to that in diet. In Study II (n = 23), we c ompared cholesterol absorption directly using [H-3]beta-sitosterol and [C-14]cholesterol, and, separately, [H-3]beta-sitostanol and [C-14]ch olesterol. We found that mean absorption between the two methods was s imilar (45% +/- 11% versus 44% +/- 10%, respectively, P difference = 0 .40), and the two methods correlated well with one another (r = 0.83) when samples from all available days were used. Variability between th e two methods was greater in individuals who absorbed more than 40% of cholesterol. Cholesterol loss on day 2 estimated from use of beta-sit ostanol as a nonabsorbable marker was predictive of absorption using r atios from days 4-6 (r = 0.80). These results suggest that, for the ma jority of subjects, beta-sitosterol is a valid nonabsorbable marker fo r cholesterol absorption.