Volume 91, Issue 4, April (2004), pp. 567-574 © The Author 2004
doi:10.1079/BJN20041087

Urinary isoflavone kinetics: the effect of age, gender, food matrix and chemical composition

Marian S. Faughnan¹, Ann Hawdon¹, Eric Ah-Singh¹, Jonathan Brown¹, D. J. Millward¹ and Aedin Cassidy^1,2
1School of Biological Sciences, University of Surrey, Guildford GU2 5XH, UK
²School of Medicine, Health Policy+Practice, University of East Anglia, Norwich, NR4 7TJ

 (Received 16 July 2003–Revised 28 November 2003–Accepted 17 December 2003)

Urinary isoflavone excretion is used to monitor compliance and examine biological effects. The present study determined if there were alterations in urinary isoflavone excretion following the ingestion of different soya foods and if age and gender potentially modified profiles. Twenty premenopausal women, seventeen post-menopausal women and twenty men received a defined single oral bolus dose (0·44mg isoflavones/kg body weight) of soya milk, textured vegetable protein (TVP) or tempeh on three separate occasions. Baseline and four consecutive complete 24h pooled urines were collected during each period. Urinary genistein recovery was influenced by gender and food matrix. For women the urinary genistein recovery was higher following soya-milk consumption compared with TVP (P<0·05). Tempeh consumption also resulted in an increased urinary genistein recovery relative to soya milk in premenopausal women (P<0·052). No differences in urinary genistein recoveries between soya foods were observed in the men. Although urinary daidzein excretion was similar across the foods studied and was not affected by age or gender, conversion to its intestinal metabolite, equol, resulted in potential matrix and chemical composition effects; urinary equol excretion was higher (P<0·01) following tempeh ingestion among equol producers. Together these data suggest that the fractional absorption of genistein is potentially different in men and women and is influenced by the food matrix and chemical composition. Furthermore, the data suggest that the metabolism of daidzein may be altered by the chemical composition of the isoflavones ingested. Further studies are required to examine the effect of higher intake and define the relative influence of these factors in elderly population groups.

Keywords:
Soya, Isoflavones, Bioavailability

Abbreviations:
m/z, mass:charge ratio, TVP, textured vegetable protein