Thursday 2 July 2009

T05019: Absorption, distribution and metabolism of isoflavones in vivo

Wednesday 14 July 2004

This research project aims to determine the fate of phytoestrogens in the human body.

Study Duration
Contractor
Background
Research Approach
Results and findings
Dissemination information
Contact

Study Duration : January 1998 to July 2001

Contractor : University of Surrey

Background

In order to assess the possible health effects of phytoestrogens, the fate of these compounds within the human body must be understood. This project aims to investigate the absorption, distribution, metabolism and excretion of the isoflavone phytoestrogens genistein and daidzein.

Research Approach

Four human studies will be performed, and will involve premenopausal women (n=10) consuming capsules containing labelled (¹³ C) genistein or daidzein. The level of labelled genistein and daidzein will be measured in blood, breath, urine and faecal samples.
The first study will examine the metabolism of a single dose of labelled isoflavones. In the second study, dose-related changes in phytoestrogen metabolism will be investigated. The third study will analyse the effects of ingestion of phytoestrogen-rich foods prior to administration of the labelled isoflavones. The fourth study will investigate whether the metabolism of daidzein or genistein can vary within an individual.

Results and findings

The overall findings of this project are listed below:

Following ingestion, genistein and daidzein are distributed into a wide range of tissues.
Ingestion of 0.8 mg/kg body wieght daidzein or genistein led to higher levels in urine and blood than the ingestion of 0.4mg/kg body wieght.
The concentration of genistein in the blood was higher than the concentration of daidzein, possibly due to more rapid removal of daidzein from the body.
Prior consumption of phytoestrogens (50 mg isoflavones from soya milk) for 7 days before ingesting 0.4mg/kg body weight genistein or daidzein does not alter the bioavailability of either phytoestrogen.
The urine samples of four of the ten subjects who received the [¹³C]daidzein doses contained [¹³C]equol, a metabolite that is produced by micro-organisms in the intestines and which is a more potent oestrogen than daidzein.
The period of time required for the amount of genistein and daidzein to reduce by 50% (i.e. the half-life) was 7.72 hours and 7.75 hours respectively, indicating that isoflavones have a short half-life in the body.
Neither genistein nor daidzein could be detected in faecal samples, suggesting that they are not excreted from the body in faeces or are extensively metabolised in the gut.
There is good reproducibility in the metabolic fate of genistein and daidzein within a given individual, but differences exist between individuals.

The results of this project were evaluated by the Committee on Toxicity (COT) as part of its review on phytoestrogens and health .

Dissemination information

Final report is available from the FSA Library and Information centre.
To obtain a copy, please contact the Enquiry Desk, Dr Elsie Widdowson Library and Information Services, Food Standards Agency tel: 020 7276 8181/8182 or email: library&info@foodstandards.gsi.gov.uk .

Publications

Faughnan, M.S., Hawdon, A., Ah-Singh, E., Brown, J., Millward, D.J. and Cassidy, A. (2004). Urinary isoflavone kinetics: the effect of age, gender, food matrix and chemical composition. Br J Nutr 91,567-74.

Setchell, K.D., Faughnan, M.S., Avades, T., Zimmer-Nechemias, L., Brown, N.M., Wolfe, B.E., Brashear, W.T., Desai, P., Oldfield, M.F., Botting, N.P. and Cassidy, A. (2001). Comparing the pharmacokinetics of daidzein and genistein with the use of 13C-labeled tracers in premenopausal women. Am J Clin Nutr 77, 411-9.

Presentations

2001 The absorption, distribution, metabolism and excretion of [¹³C]daidzein and [¹³C]genistein in vivo. Seventeenth International Congress of Nutrition. Vienna, Austria

2001 Comparison of the absorption, distribution, metabolism and absorption of [¹³C]daidzein and [¹³C]genistein in vivo . Fourth International Conference on the Role of Soy in Preventing Chronic Disease. San Diego, USA

Contact : For any enquiries concerning this research project, please contact the relevant Programme contact or email: science@foodstandards.gsi.gov.uk

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T05019: Absorption, distribution and metabolism of isoflavones in vivo

Background

Research Approach

Results and findings

Dissemination information

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