Concentrations of isoflavones in plasma and urine of post-menopausal women chronically ingesting high quantities of soy isoflavones

J. Mathey, V. Lamothe, V. Coxam, M. Potier, P. Sauvant, C. Bennetau -Pelissero
Journal of Pharmaceutical and Biomedical Analysis. 2006-06-01; 41(3): 957-965
DOI: 10.1016/j.jpba.2006.01.051

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1. J Pharm Biomed Anal. 2006 Jun 7;41(3):957-65. doi: 10.1016/j.jpba.2006.01.051.
Epub 2006 Mar 2.

Concentrations of isoflavones in plasma and urine of post-menopausal women
chronically ingesting high quantities of soy isoflavones.

Mathey J(1), Lamothe V, Coxam V, Potier M, Sauvant P, Bennetau-Pelissero C.

Author information:
(1)Groupe Ostéoporose, U3M, INRA Theix, 63122 Saint Genès-Champanelle, France.

Soy food or food supplements based on soy containing isoflavones (Isos) are
increasingly available in Western countries. However, the variability of Isos
levels in urine and plasma in humans during chronic ingestion is poorly
documented. Nevertheless, this is the way these compounds will most probably be
used in the future, especially if the soy-based supplements market goes on
increasing. Here, glycosilated Isos in an enriched extract of Prevastein equal
to 100 mg of equivalent Isos aglycone was given daily to 27 post-menopausal
women for 30 days and to 12 post-menopausal women for 60 days. Volunteers were
given Prevastein in a cereal bar (25 mg Isos) and in a yoghurt (25 mg Isos) both
at breakfast and dinner. Plasma samples were collected after overnight fasting.
Urine samples were aliquots of a 24 h collection checked on volume and creatinin
excretion levels. Genistein, daidzein and equol were measured at day 0 and every
15 days afterwards, using original specific ELISAs. Constant levels were reached
from the 15th day. About 59.2% of the volunteers were significant equol
producers in the first experiment and 58.3% in the second. A large variability
in plasma and urine levels was observed among post-menopausal women consuming
100 mg Isos per day, although remaining relatively stable in each individual
subject. This could partly account for the controversial effects of Isos
recorded so far in clinical studies. So Isos plasma levels would have to be
assayed during chronic exposures, and could help to better understand the large
variability of the effects classically observed in clinical studies. ELISA
techniques could be easily exported to analytical laboratories to help
physicians and nutritionists with their prescriptions.