4 high or low isoﬂavone soy protein diet; however, the woman on the control diet had a signiﬁcant decrease of BMD and BMC during this time. The women who had more bone loss had higher BAP levels. Therefore BAP may be a better indicator of bone turnover than bone formation [38]. The lumbar spine seems to beneﬁt the most from consumption of soy phytoestrogens. A 24-week long study with postmenopausal women consuming soy protein with 90 mg isoﬂavones/day showed a signiﬁcant increase in BMD of the lumbar spine, with no eﬀect on the femoral neck or total body BMD [40]. There were no BMD eﬀects in woman consuming soy protein with 56 mg isoﬂavones/day [40]. The only study to examine the eﬀects of soy isoﬂavones in premenopausal women showed no eﬀect on bone mineral density levels [41], while signiﬁcant eﬀects were observed in postmenopausal women in this study. Brink et al. [42] carried out studies in healthy men (59.2 ± 17.6 y), who were assigned to consume 40 g of either SP or milk-based protein (MP) daily for 3 mo in a double-blind, randomized, controlled, parallel design. Serum insulin-like growth factor-I (IGF-I), which is associ- ated with higher rates of bone formation, was greater (P < .01) in men supplemented with SP than in those consuming MP. Serum alkaline phosphatase and bone-speciﬁc alkaline phosphatase activities, markers of bone formation, and urinary deoxypyridinoline excretion, a speciﬁc marker of bone resorption, were not diﬀerent between the SP and MP groups. Furthermore, because substantial reductions in bone density occur in men at ∼65 y of age, these authors analyzed separately data for men ≥65 y and those <65 y of age. The response to protein supplementation was consistent in the two age groups. The eﬀects of SP on serum IGF-I levels suggest that SP may positively inﬂuence bone in men. It should however be mentioned that their study was short, so longer-duration studies examining the eﬀects of SP or its isoﬂavones on bone turnover and bone mineral density and content in men are warranted. There are studies showing that the consumption of isoﬂavones has no any beneﬁts for women in early post- menopausal period. Brink et al. [42] conducted a ran- domized, double-blind, placebo-controlled, parallel, mul- ticenter trial in two hundred thirty-seven healthy early postmenopausal women (mean (±SD) age of 53 ± 3 y and time since last menses of 33 ± 15 mo), who consumed isoﬂavone-enriched foods providing a mean daily intake of 110 mg isoﬂavone aglycones or control products for 1 y while continuing their habitual diet and lifestyle. These authors found that Consumption of isoﬂavone-enriched products did not alter bone mineral density of the lumbar spine and total body or markers of bone formation and bone resorption. Furthermore, Hormone concentrations did not diﬀer between the isoﬂavone and control groups. The intake of isoﬂavone-enriched products resulted in increased isoﬂavone concentrations in plasma and urine, whereas control products did not. A recent meta-analysis by Liu et al. [43] showed only very slight beneﬁts of soy isoﬂavones in increasing BMD in women. These authors identiﬁed 10 eligible RCTs in 896 women. A mean dose of 87 mg soy isoﬂavones for at least Journal of Osteoporosis one year did not signiﬁcantly aﬀect BMD changes. The mean (95% CI) diﬀerences in BMD changes (in mg/cm2/year) were 4.1 (−1.6, 9.8) (0.4%) at the lumbar spine, −1.5 (−7.2, 4.3) (−0.3%) at the femoral neck under random- eﬀects model, and 2.5 (−0.5, 5.4) (0.2%) at the total hip by ﬁx-eﬀects model, respectively. Similar results were obtained in subgroup analyses by isoﬂavone sources (soy protein versus isoﬂavone extract), ethnic diﬀerences (Asian versus Western). Larger dose (≥80 mg/d), but not lower dose (<80 mg/d), of isoﬂavone intervention tended to have a weak beneﬁcial eﬀect on spine BMD (P = .08 versus P = .94). Liu et al. [43] concluded that soy isoﬂavone supplementation is unlikely to have signiﬁcant favorable on BMD at the lumbar spine and hip in women. 4. Isoﬂavones and Bone Health: Mechanisms of Action Soy isoﬂavones are natural products that could be used as an alternative to menopausal hormone therapy because they are structurally and functionally related to 17beta- estradiol. Results of mechanistic studies indicate that soy or its isoﬂavones, while suppressing the rate of bone resorption concomitantly enhance the rate of bone formation. In ovariectomized rats, soy isoﬂavones have been shown [32, 33] to reduce the urinary excretion of deoxypyridinoline (Dpd), a speciﬁc marker of bone resorption. Similarly, at least three human studies have clearly demonstrated the anti- resorptive properties of soy or its isoﬂavones. One of these studies was a cross-sectional study by Horiuchi et al. [44], in which soy protein intake in Japanese postmenopausal women was associated with lower urinary Dpd excretion. In the second study, postmenopausal women who were assigned to a soy milk regimen, providing 60–70 mg of isoﬂavones, experienced a signiﬁcant decrease in urinary N- terminal cross-linked peptide, another speciﬁc marker of bone resorption [45]. Arjmandi et al. [46] reported that the daily consumption of 40 g soy protein, but not milk protein, for three months by postmenopausal women who were not on HRT signiﬁcantly reduced the urinary excretion of Dpd. Ma et al. [47] and Choi et al. [48] carried out a meta-analysis of nine studies with a total of 432 sub- jects on the impact of isoﬂavone consumption on bone markers. They found that urinary Dpd concentration in subjects who consumed isoﬂavones decreased signiﬁcantly by −2.08 nmol/mmol (95% conﬁdence interval (CI): −3.82 to −0.34 nmol/mmol) in comparison with that in subjects who did not consume isoﬂavones. Isoﬂavone intake versus placebo intake signiﬁcantly increased BAP by 1.48 μg/L (95% CI: 0.22–2.75 μg/L). Decreases in the urinary Dpd concentra- tion with isoﬂavone intake of <90 mg/day and with treatment lasting less than 12 weeks were −2.34 nmol/mmol (95% CI: −4.46 to −0.22 nmol/mmol) and −2.03 nmol/mmol (95% CI: −3.20 to −0.85 nmol/mmol), respectively. It is reasonable to suggest that soy or its isoﬂavones enhance bone formation based on at least two lines of evidence: (1) soy isoﬂavones stimulate osteoablastic activity through activation of estrogen receptors [47, 48], and (2) soy