The bioavailability of the soy isoflavones genistein and daidzein, and metabolism of the latter to form equol, is higher after soymilk consumption than soy germ, says a new study.
Moreover, gut microflora populations and an increased intake of omega-3 fatty acids were also associated with increased equol production, indicate the results of the randomised dietary intervention trial with 100 healthy postmenopausal women published in the Journal of Nutrition.
Equol is formed exclusively by bacteria in the gut, but only about a third of all Caucasians possess the necessary gut microflora capable of converting daidzein into equol. The health benefits of soy food diets are reported to more efficient in so-called 'equol producers'.
Marian Verbruggen, co-author of the study and head of medical sciences and regulatory affairs for Frutarom Netherlands told NutraIngredients.com that the study helps us to understand the large individual variation we observe in physiological response to isoflavones in clinical trials and the complex metabolism of isoflavones.
"The more we understand of the metabolism and in relation to this the bio-availability, the industry gets knowledge and tools to select the right ingredients for their products," she said.
"In the end the consumer will benefit from this, with the availability of high quality products."
Lead author Selin Bolca, from Ghent University, and co-workers recruited 100 postmenopausal women (average age 57, average BMI 23.9 kg per sq. m) and, after an initial four-day stabilisation period, randomly assigned them to a receive three portions per day of soymilk or soy germ containing 28.51 and 37.99 mg isoflavone aglycone equivalents per portion for five days.
Urine samples, taken over the 24 hours of the last day, showed that genistein and daidzein concentrations were higher when the isoflavones were consumed from soymilk rather than the soy germ tablets.
By classifying the individuals as poor, moderate, and strong equol producers, the researchers observed that higher counts of the bacteria Clostridium coccoides-Eubacterium rectale were associated with less equol, while increased sulfate-reducing bacteria counts was associated with increased equol production.
Moreover, an increased dietary intake of polyunsaturated fatty acids (PUFAs) was associated with increased equol production.
"PUFA are concentrated in foods such as fish and seafood, which are not generally consumed on a daily basis in western countries," wrote the researchers.
"In Japan and Korea, however, the diet is low in red meat and often rich in fish; thus, PUFA accounts for a larger proportion of the total fat intake, which may explain why the prevalence of strong equol producers is higher in these countries," they added.
The researchers noted a good correlation between the urinary excretion profiles and equol production and the subjects' phenotypes based on the daidzein metabolism by faecal cultures.
This shows "the potential of faecal incubations to identify equol producers without dietary intervention," they said.
The study was funded by Alpro NV and Frutarom Netherlands. The study and analyses were independent, however, state the researchers.
Source: Journal of Nutrition
Volume 137, Pages 2242-2246
"Microbial and Dietary Factors Are Associated with the Equol Producer Phenotype in Healthy Postmenopausal Women"
Authors: S. Bolca, S. Possemiers, A. Herregat, I. Huybrechts, A. Heyerick, S. De Vriese, M. Verbruggen, H. Depypere, D. De Keukeleire, M. Bracke, S. De Henauw, W. Verstraete, T. Van de Wiele