The effects of green kiwifruit combined with isoflavones on equol production, bone turnover and gut microflora in healthy postmenopausal women

Background and Objectives: Isoflavone (daidzein and genistein) interventions in postmenopausal women have produced inconsistent skeletal benefits, partly due to population heterogeneity in daidzein metabolism to equol by enteric bacteria. This study assessed changes in microflora and bone turnover in response to isoflavone and kiwifruit supplementation in New Zealand postmenopausal women. Methods and Study Design: Healthy women 1-10 years post-menopause were randomly allocated to group A (n = 16) or B (n = 17) for a 16-week crossover trial. Two consecutive 6-week treatment periods had a 2-week lead-in period at intervention commencement and a 2-week washout period between treatments. Treatments prescribed either (1) daily isoflavone supplementation (50 mg/day aglycone daidzein and genistein) alone, or (2) with two green kiwifruit. At treatment baseline and end-point (four time points) the serum bone markers C Telopeptide of Type I collagen (CTx), undercarboxylated osteocalcin (unOC), and serum and urinary daidzein and equol, were measured. Changes in gut microflora were monitored in a subgroup of the women. Results: Equol producers made up 30% of this study population (equol producers n = 10; non-equol producers n = 23) with serum equol rising significantly in equol producers. Serum ucOC decreased by 15.5% (p < 0.05) after the kiwifruit and isoflavone treatment. There were no changes in serum CTx or in the diversity of the gut microflora. Conclusions: 50 mg/day isoflavones did not reduce bone resorption but kiwifruit and isoflavone consumption decreased serum ucOC levels, possibly due to vitamin K1 and/or other bioactive components of green kiwifruit.