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

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 t_1/2 for 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.