Gastrointestinal absorption and plasma kinetics of soy Δ5-phytosterols and phytostanols in humans

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Abstract
Our objective was to measure the systemic absorption of lecithin-emulsified Δ5-phytosterols and phytostanols during test meals by use of dual stable isotopic tracers. Ten healthy subjects underwent two single-meal absorption tests in random order 2 wk apart, one with intravenous dideuterated Δ5-phytosterols and oral pentadeuterated Δ5-phytosterols and the other with the corresponding labeled stanols. The oral-to-intravenous tracer ratio in plasma, a reflection of absorption, was measured by a sensitive negative ion mass spectroscopic technique and became constant after 2 days. Absorption from 600 mg of Δ5-soy sterols given with a standard test breakfast was 0.512 ± 0.038% for sitosterol and 1.89 ± 0.27% for campesterol. The absorption from 600 mg of soy stanols was 0.0441 ± 0.004% for sitostanol and 0.155 ± 0.017% for campestanol. Reduction of the double bond at position 5 decreased absorption by 90%. Plasma t½for stanols was significantly shorter than that for Δ5-sterols. We conclude that the efficiency of phytosterol absorption is lower than what was reported previously and is critically dependent on the structure of both sterol nucleus and side chain.