Ten RCTs (n=608) were included.
Six studies scored 5 out of 5 points on the Jadad quality scale, three scored 4 points and one scored 3 points (the criteria not met were reported).
Isoflavones were associated with a statistically significant increase in SBMD compared with placebo (WMD 20.6 mg/cm2, 95% confidence interval, CI: 4.5, 36.6, p=0.01), based on 10 studies (16 comparisons). The authors reported that the results were inconsistent among studies but did not report results of formal tests for heterogeneity.
Subgroup analyses showed increases in SBMD to be statistically significant for:
studies of isolated soy protein (WMD 21.3 mg/cm2, 95% CI: 3, 39.7; 7 studies, n=460), but not isoflavone tablets (3 studies, n=148);
studies using an isoflavone intake of more than 90 mg/day (WMD 28.5 mg/cm2, 95% CI: 8.4, 48.6; 6 studies, n=352), but not those using a lower dose (7 studies, n=318);
studies lasting 6 months (WMD 27 mg/cm2, 95% CI: 8.3, 45.8; 5 studies, n=277), but not those lasting more than 12 months (4 studies, n=310);
studies of Caucasian women (WMD 21.3/cm2, 95% CI: 3, 39.7; 7 studies, n=460), but not Asian women (3 studies, n=148); and
studies of postmenopausal women (WMD 22.4 mg/cm2, 95% CI: 5.3, 39.5; 8 studies, n=511), but not perimenopausal women (2 studies, n=97).
None of these subgroup analyses showed significant heterogeneity.
Isoflavones were associated with a non statistically significant increase in SBMC compared with placebo (WMD 0.93 g, 95% CI: -0.37, 2.24, p=0.08), based on 6 studies (9 comparisons).
The funnel plot showed no strong evidence of publication bias.