by Dr. Lise Alschuler, ND, FABNO A recent randomized, placebo controlled double blinded two year clinical trial, the Soy Phytoestrogens as Replacement Estrogens (SPARE) trial, failed to find a protective effect of soy on bone density or rate of bone

by Dr. Lise Alschuler, ND, FABNO

A recent randomized, placebo controlled double-blinded two year clinical trial, the Soy Phytoestrogens as Replacement Estrogens (SPARE) trial, failed to find a protective effect of soy on bone density or rate of bone turnover in postmenopausal  women who did not have osteoporosis at baseline.  The intervention was soy isoflavones pills (Novasoy; Archer Daniels Midland Company) providing 200 mg of soy isoflavones per day. This study confirms the findings of two earlier studies that failed to show a protective effect from soy on bone loss, but contradicts an Italian multi-center study that showed bone protection from genistein given at half the dose (58mg) over 2 years. So what is going on? 

While the study design and statistical analysis of the SPARE trial appears sound, there was a high dropout rate which could have reduced the power of the trial to demonstrate an effect from the soy. Additionally, I found that the analysis failed to query for other characteristics in these women’s diets that may have modified the effect of soy.  And, the women did not appear to be a particularly healthy bunch to begin with. More than half of the women in both the soy and the placebo groups had ‘adverse effects’ of abdominal bloating, and almost half of each group had headaches and a variety of other symptoms.  Were these reactions to the interventions, or were these evidence of women in less than optimal health and therefore less likely to respond to one intervention?  Were the bacteria in the intestines of the U.S. women in the SPARE study different than in the Italian women in the study that showed  benefit, thereby affecting the metabolism of genestein into equol  – the beneficial metabolite? These are just a few unanswered questions, but questions that certainly raise the possibility of alternative conclusions.

My Take-Away: 

Soy isoflavones are unlikely to emerge as the most reliable way to prevent bone loss in menopausal women. However, the potential for soy to be of benefit in this regard remains, and, given the overall health benefits of soy, deserves closer scrutiny. My ideal study would examine the effects of organic, non-GMO whole food soy versus placebo in menopausal women without symptoms of ill health or menopause to begin with and with laboratory assessed eubiotic bowels.  Until then, I will continue to enjoy my tofu and edamame.

Citation: Levis S. et al. Arch Intern Med. 2011;171(15):1363-1369

 

 

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