Why are soy milk, foods, and supplements so popular among women?
Evidence that soy may help prevent breast cancer is one reason – although the evidence is mixed, and soy is high in omega-6s fats, which tend to promote tumor growth – see “Soy Link to Breast Health Gets a Boost”.
Some want a high-protein alternative to meat or dairy foods … or a natural way to address menopausal complaints like bone loss, hot flashes, vaginal dryness, and insomnia.
Estrogen therapy – with or without progesterone – can alleviate most of these menopausal changes.
But recent results from the Women's Health Initiative study suggest that the overall risks of estrogen therapy may outweigh its benefits.
As a consequence of these worrisome WHI findings – or because of a simple desire to avoid drugs – many menopausal women seek out soy supplements instead.
How soy gained glory ... and came to grief
The soy fad began with epidemiological studies among Asian women, which linked higher soy intake to lower risk of bone fractures, without being able to prove any connection.
And the presence in soy of estrogen-like compounds fueled sale of soy supplements with alleged benefits for osteoporosis, hot flashes, and breast cancer.
(The estrogen-mimics in soybeans are polyphenol compounds called isoflavones … specifically, genistein and daidzein.)
Many studies have examined whether soy protein powders or soy isoflavone supplements produce significant, consistent benefits with regard to menopause-related conditions.
So far, the results of clinical studies have been mixed, with most finding no significant benefits.
Earlier this month, the European Food Safety Authority rejected all proposed health claims for soy isoflavones, including their ability to improve menopause symptoms, reduce LDL cholesterol, or produce antioxidant effects.
And two recent U.S. studies failed to find any menopausal bone-preservation benefits from soy (USDA 2010; ISU 2010)
Now, the negative outcomes of a clinical trial from Florida cast further doubt on the alleged benefits of soy powders and pills.
Florida trial finds soy useless for bone health or menopausal symptoms
The clinical trial was led by Dr. Silvina Levis from the Miami Veterans Affairs Healthcare System and Miller School of Medicine, at the University of Miami (Levis S et al. 2011).
Levis and her team conducted a randomized controlled trial over a five-year period, to determine the effectiveness of soy isoflavone tablets in preventing bone loss and other menopausal symptoms.
The researchers recruited 248 women aged 45 to 60 who were in their first five years of menopause … 126 were randomly assigned to the placebo-tablet group and 122 received a test tablet providing 200 mg of soy isoflavone.
This is about twice the highest intake of soy isoflavone through food sources in a typical East Asian diet, and higher than the doses used in many prior trials, to ensure an adequate amount.
After two years, the Miami team saw no significant differences between the soy isoflavone group and placebo group regarding changes in bone mineral density at the spine, hip, or femoral (thigh bone) “neck”.
And the soy group showed no advantages with regard to menopausal symptoms, vaginal cell characteristics, bone collagen, blood fats, or thyroid function.
Last but not least, significantly more women in the soy group suffered hot flashes and constipation, compared with the control group.
As the researchers wrote, “… our population of women in the first five years of menopause, on average, had low rates of bone loss, and that 200 mg of soy isoflavone tablets taken once daily does not prevent bone loss or reduce bone turnover or menopausal symptoms.” (Levis S et al. 2011)
Some observers say that soy foods are actively unhealthful, especially when consumed frequently … for more on that topic, see The Weston A. Price Foundation’s “Soy Alert” page.
We tend to believe that it’s probably safe to enjoy natural soy foods in moderation … as hundreds of millions of healthy, long-lived East Asians have done over the past 200 years or more.
Just don’t expect much if you use soy supplements to alleviate symptoms of menopause.
Bolaños R, Del Castillo A, Francia J. Soy isoflavones versus placebo in the treatment of climacteric vasomotor symptoms: systematic review and meta-analysis. Menopause. 2010 May-Jun;17(3):660-6. Review.
Brink E, Coxam V, Robins S, Wahala K, Cassidy A, Branca F; PHYTOS Investigators. Long-term consumption of isoflavone-enriched foods does not affect bone mineral density, bone metabolism, or hormonal status in early postmenopausal women: a randomized, double-blind, placebo controlled study. Am J Clin Nutr. 2008 Mar;87(3):761-70.
Castelo-Branco C, Cancelo Hidalgo MJ. Isoflavones: effects on bone health. Climacteric. 2011 Apr;14(2):204-11. Epub 2010 Nov 17. Review.
Evans EM, Racette SB, Van Pelt RE, Peterson LR, Villareal DT. Effects of soy protein isolate and moderate exercise on bone turnover and bone mineral density in postmenopausal women. Menopause. 2007 May-Jun;14(3 Pt 1):481-8.
Harkness LS, Fiedler K, Sehgal AR, Oravec D, Lerner E. Decreased bone resorption with soy isoflavone supplementation in postmenopausal women. J Womens Health (Larchmt). 2004 Nov;13(9):1000-7.
Iowa State University (ISU). Multicenter study finds little effect of soy isoflavones on bone loss in postmenopausal women. February 9, 2010. Accessed at http://www.eurekalert.org/pub_releases/2010-02/isu-msf020910.php
Kelley KW, Carroll DG. Evaluating the evidence for over-the-counter alternatives for relief of hot flashes in menopausal women. J Am Pharm Assoc (2003). 2010 Sep-Oct;50(5):e106-15. Review.
Levis S et al. Soy Isoflavones in the Prevention of Menopausal Bone Loss and Menopausal Symptoms: A Randomized, Double-blind Trial. Arch Intern Med. 2011;171(15):1363-1369. doi:10.1001/archinternmed.2011.330. Accessed at http://archinte.ama-assn.org/cgi/content/short/171/15/1363
Levis S, Griebeler ML. The role of soy foods in the treatment of menopausal symptoms. J Nutr. 2010 Dec;140(12):2318S-2321S. Epub 2010 Nov 3. Review.
Levis S, Strickman-Stein N, Doerge DR, Krischer J. Design and baseline characteristics of the soy phytoestrogens as replacement estrogen (SPARE) study--a clinical trial of the effects of soy isoflavones in menopausal women. Contemp Clin Trials. 2010 Jul;31(4):293-302. Epub 2010 Mar 15.
Mori M, Aizawa T, Tokoro M, Miki T, Yamori Y. Soy isoflavone tablets reduce osteoporosis risk factors and obesity in middle-aged Japanese women. Clin Exp Pharmacol Physiol. 2004 Dec;31 Suppl 2:S39-41.
Ricci E, Cipriani S, Chiaffarino F, Malvezzi M, Parazzini F. Soy isoflavones and bone mineral density in perimenopausal and postmenopausal Western women: a systematic review and meta-analysis of randomized controlled trials. J Womens Health (Larchmt). 2010 Sep;19(9):1609-17.
United States Department of Agriculture (USDA). Do soy isoflavones boost bone health? July 30, 2010. Accessed at http://www.eurekalert.org/pub_releases/2010-07/usdo-dsi073010.php