a1 Cancer Prevention Program, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave North, M4-B402, PO Box 19024, Seattle, WA 98109-1024, USA
a2 Department of Epidemiology, University of Washington, Seattle, WA, USA
a3 Interdisciplinary Program in Nutritional Sciences, University of Washington, Seattle, WA, USA
a4 Department of Chemistry, University of Helsinki, Helsinki, Finland
a5 Epidemiology Program, Fred Hutchinson Cancer Research Center, Seattle, WA, USA
Particular intestinal bacteria are capable of metabolizing the soya isoflavone daidzein to equol and/or O-desmethylangolensin (O-DMA), and the presence of these metabolites in urine after soya consumption are markers of particular intestinal bacteria profiles. Prevalences of equol producers and O-DMA producers are approximately 30–50 % and 80–90 %, respectively, and limited observations have suggested that these daidzein-metabolizing phenotypes are stable within individuals over time. Characterizing stability of these phenotypes is important to understand their potential as markers of long-term exposure to particular intestinal bacteria and their associations with disease risk. We evaluated concordance within an individual for the equol-producer and O-DMA-producer phenotypes measured at two time points (T1, T2), 1–3 years apart. Phenotypes were ascertained by analysing equol and O-DMA using GC-MS in a spot urine sample collected after 3 d soya (source of daidzein) supplementation. In ninety-two individuals without recent (within 3 months before phenotyping) or current antibiotics use, 41 % were equol producers at T1 and 45 % were equol producers at T2, and 90 % were O-DMA producers at T1 and 95 % were O-DMA producers at T2. The percentage agreement for the equol-producer phenotype was 82 and for the O-DMA-producer phenotype was 89. These results indicate that these phenotypes are stable in most individuals over time, suggesting that they provide a useful biomarker for evaluating disease risk associated with harbouring particular intestinal bacteria responsible for, or associated with, the metabolism of the soya isoflavone daidzein.
(Received April 18 2005)
(Accepted July 09 2005)