Influence of 10 wk of soy consumption on plasma concentrations and excretion of isoflavonoids and on gut microflora metabolism in healthy adults.
BACKGROUND
Little information is currently available on the role of the gut microflora in modulating isoflavone bioavailability or on sex differences in isoflavone metabolism and bioavailability.


OBJECTIVE
We sought to determine whether chronic soy consumption influences isoflavone bioavailability as judged by plasma isoflavone concentrations and modified gut microflora activities [beta-glucoside hydrolysis and equol and O-desmethylangolensin (O-DMA) production]. We also examined whether sex differences in isoflavone metabolism exist.


METHODS
A randomized, parallel, controlled study design was used to compare a high-soy diet (104 +/- 24 mg total isoflavones/d) with a low-soy diet (0.54 +/- 0.58 mg total isoflavones/d) in 76 healthy young adults for 10 wk.


RESULTS
Concentrations of isoflavones and their gut microflora metabolites in the plasma, urine, and feces were significantly higher in the subjects who consumed the high-soy diet than in those who consumed the low-soy diet. Concentrations of O-DMA in plasma and urine were higher in the men than in the women. Fecal bacteria from subjects consuming both diets could convert daidzein to equol ex vivo. Fecal beta-glucosidase activity was significantly higher in the subjects who consumed the high-soy diet than in those who consumed the low-soy diet.


CONCLUSIONS
Although interindividual variation in isoflavone metabolism was high, intraindividual variation was low. Only concentrations of O-DMA in plasma and urine appeared to be influenced by sex. Chronic soy consumption does not appear to induce many significant changes to the gut metabolism of isoflavones other than higher beta-glucosidase activity.
Nutrition, Food and Health Research Centre, the Department of Nutrition and Dietetics, King's College London, 150 Stamford Street, London SE1 9NN, UK. helen.wiseman@kcl.ac.uk
Helen
H
Wiseman
Karen
K
Casey
Elizabeth A
EA
Bowey
Rosanna
R
Duffy
Margaret
M
Davies
Ian R
IR
Rowland
Antony S
AS
Lloyd
Alistair
A
Murray
Richard
R
Thompson
Don B
DB
Clarke
D000293:Adolescent; D000328:Adult; D001628:Beverages; D001682:Biological Availability; D060754:Equol; D005243:Feces / Q000737:chemistry* / Q000201:enzymology / Q000382:microbiology; D005260:Female; D006801:Humans; D007422:Intestines / Q000382:microbiology; D007529:Isoflavones / Q000097:blood / Q000378:metabolism* / Q000652:urine; D008297:Male; D008875:Middle Aged; D012737:Sex Factors; D013025:Glycine max / Q000737:chemistry*; D001617:beta-Glucosidase / Q000378:metabolism*
C007610:4',7-dihydroxy-3,4-dihydroisoflavone; D007529:Isoflavones; D060754:Equol; C004742:daidzein; D001617:beta-Glucosidase