Method of defining equol-producer status and its frequency among vegetarians

Author: Setchell KD, Cole SJ
Publication: J Nutr. 2006 Aug;136(8):2188-93

Intestinal bacteria produce equol from daidzin and daidzein. The amount of equol produced during digestion is very variable and depends on the individual. The first sep in the production of equol is the hydrolysis of daizin into daidzein and a sugar molecule. Daidzien is then transformed into S-equol by intestinal bacteria. Studies have shown that more than one bacterial strain is required for its production. S-equol is an estrogen receptor and potent antagonist of dihydrotestosteron. S-equol is therefore a potential phytochemical to help prevent prostate cancer and some skin conditions. Some individual who produce significant quantities of equol are defined as equol producers. Unique is that all animals, when fed with soy, seem to produce equol but only about one third of humans are equol producers. Studies have shown that equol producers give more a favourable response following the consumption of isoflavones.

The aim of this study was define criteria for equol producers. The researchers measured the serum and urine levels of equol and daidzein. The study was carried out on 41 healthy adult, of whom 29 were vegetarians. They received a soy protein drink containing 28 mg/liter daidzein. The serum and urine levels of equol showed large difference between individuals. For example, serum equol levels ranged from 10 to 139 nmol/liter. Other researchers have used serum equol levels or urinary equol levels to define equol producer status. The log 10 transformed ratio of urinary equol to daidzein was developed and used as a better measure of equol producer status. This method was used because it was independent on the quantiy of ingested daidzein and analytical method to measure isoflavones.

A log 10 transformed ratio of higher than -1.75 classifies the individual as an equol producer. The frequency of equol producers is about 60% for vegetarians and 25% for non-vegetarians. There was also a big difference in equol producer status between male and female. Men were about 3 times more likely to de equol producers. The study suggested that dietary components other than soy influence equol production.