Soy isoflavones show bone health benefits for older women – regardless of equol production

Fifty days of isoflavone consumption increased bone calcium retention by up to 7.6%, report scientists from Purdue University, Indiana University School of Medicine, and the University of Alabama at Birmingham.

While the isoflavones did not improve calcium retention as much as a bisphosphonate (risedronate) intervention, the potential bone health benefits were observed regardless of the women’s equol-producing status, and mixed isoflavones in their natural ratios are more effective than enriched genistein.

“A moderate dose (but higher than that used in randomized controlled trials of BMD) of mixed isoflavones in their natural proportion was the most-effective isoflavone supplement at improving bone calcium retention compared with the effects of supplements that were more rich in genistein and higher in the total isoflavone content,”​ wrote the authors in the Journal of Nutrition​​.

“Compared with bisphosphonates and HRT, the use of soy isoflavones presents minimal to negligible risk to postmenopausal women and can be used long term for some protection against postmenopausal bone loss.”​

Estrogen-like effects​

Isoflavones are well known phytoestrogens - active substances derived from plants that have a weak estrogen-like action.

Isoflavones from soy have been shown to provide a number of health benefits, including the promotion of heart health and the maintenance of bone health in post-menopausal women.

The new study found that a mixture of genistein, daidzein, and glycitein at a dose of 105.23 mg total isoflavones per day as genistein, daidzein, and glycitein in their natural ratios was the most effective dose, and increased bone calcium retention by 7.6%.

In comparison, risedronate increased bone calcium retention by 15.3%, said the researchers.

On the other hand, data from the 24 participants of the blinded, randomized, crossover intervention trial, a genistein-rich soy supplement (52.85 mg/d of genistein) was found to only increase bone calcium retention by 3.4%.

Equol​

The study also considered if a woman’s ability to produce equol influenced the results. 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 (fewer than 13% of the women in this study were equol producers). The health benefits of soy food diets are reported to more efficient in so-called 'equol producers'.

“To our knowledge, we are the first to a priori screen individuals for their equol-producing ability to compare differences in bone responses to a soy intervention,” ​wrote the researchers. “The equol-producing ability did not enhance the bone-protective effect of soy isoflavones in postmenopausal women.”​

Source: Journal of Nutrition​​
Volume 102, Number 3, Pages 695-703, doi: 10.3945/ajcn.114.093906
“Impact of equol-producing capacity and soy-isoflavone profiles of supplements on bone calcium retention in postmenopausal women: a randomized crossover trial”​
Authors: J.W. Pawlowski, B.R. Martin, G.P. McCabe, et al.