Postmenopausal women tend to struggle with deteriorating bone health, but the results of isoflavone (daidzein and genistein) interventions among them have so far been inconsistent.
As such, researchers from New Zealand's Massey University, the Tokyo University of Agriculture, and Japan's National Institute of Health and Nutrition conducted a study to assess how isoflavone and kiwifruit supplementation affected microflora and bone turnover in postmenopausal women.
They recruited 33 healthy postmenopausal women (one to 10 years post-menopause) and randomly assigned them to two groups for a 16-week crossover trial.
This entailed a two-week lead-in period at the start of the intervention, followed by two consecutive six-week treatment periods, and a two-week washout period between treatments.
In one group, each participant was given a daily 50mg of isoflavone supplementation, while in the other group, participants were given the same treatment, but with two green kiwifruit.
The researchers discovered that bone resorption was not reduced by isoflavone supplementation.
However, the combined supplementation of kiwifruit and isoflavones decreased serum uncarboxylated osteocalcin (ucOC), which is inversely associated with bone mineral density by 15.5%, while the isoflavone supplement alone caused a significant elevation.
At the same time, the researchers noted no changes in in the diversity of the participants' gut microflora.
Bettering the benefits
The researchers then wrote that while the daily 50mg dosage of isoflavones did not reduce bone resorption, the combination of kiwifruit and isoflavones lowered serum ucOC levels, likely because of vitamin K1 and / or other bioactive components of green kiwifruit.
In conclusion, they stated: "We conclude from these findings that kiwifruit can significantly augment the bone health benefits of isoflavones by improving vitamin K status.
"It will be of interest to assess whether kiwifruit can further improve bone health and alter gut microbiota over a longer period of time.”
Source: Asia Pacific Journal of Clinical Nutrition
"The effects of green kiwifruit combined with isoflavones on equol production, bone turnover and gut microflora in healthy postmenopausal women"
Authors: Marlena C Kruger, et al.