Can Soy Reduce Postmenopausal Osteoporosis?

Lumbar spine - mensatic

Although estrogen protects women against bone loss during fertile years, bone deterioration (osteoporosis) begins at menopause. Due to concerns about the safety of estrogen replacement, women may want to use the naturally-occurring soy phytoestrogens (plant substances that mimic some estrogen functions) to retard bone loss. The primary phytoestrogens in soy are: daidzein, genistein and glycitein.

Clinical Studies of Soy Phytoestrogens and Osteoporosis

Some studies have found that soy phytoestrogens are modestly effective in reducing bone loss. Among the positive studies:

• A 2000 study in Japan selected 69 perimenopausal woman and treated 24 with a phytoestrogen-rich soy protein (80.4 mg genistein/day), treated 24 with a phytoestrogen-poor soy protein (4.4 mg genistein/day), and treated 21 women with a control (no phytoestrogen) product (whey). After 24 weeks of the treatments, the researchers measured bone mineral density (BMD) in the women's lumbar spine.

1. the women in the control (no phytoestrogen) group lost 1.28% BMD control (no phytoestrogen) group lost 1.28% BMD
2. the women in the phytoestrogen-poor group lost 0.66% BMD
3. the women in the phytoestrogen-rich group lost 0.20% BMD (Alekel DL, St Germain A, Peterson CT, Hanson KB, Stewart JW, and T Toda. 2000. Isoflavone-rich soy protein isolate attenuates bone loss in the lumbar spine of perimenopausal women. Am J Clin Nutr 72:844-52)

• A 1998 study at the University of Illinois recruited 66 postmenopausal women and treated 33 women with a high-phytoestrogen soy protein (~80 mg phytoestrogen/day), treated 33 with moderate-phytoestrogen soy protein (~4 mg/day), and treated 33 with control milk protein. Both of the soy protein groups had supplementation with calcium to match the calcium in milk protein. After 24 weeks of treament, BMD was measured in the lumbar spine and femur with the following results:

1. the women receiving the control milk protein lost 0.64% BMD
2. the women receiving the moderate-phytoestrogen soy protein lost 0.21% BMD
3. the women receiving the high-phytoestrogen soy protein gained 1.02% BMD (Potter SM, Baum JA, Teng H, Stillman RJ, Shay NF, and JW Erdman Jr. 1998. Soy protein and isoflavones: their effects on blood lipids and bone density in postmenopausal women. Am J Clin Nutr 68:137S-139S)

• A 2008 trial in Europe recruited 237 healthy, early postmenopausal women and administered soy-enriched biscuits and bars providing a mean daily intake of 110 mg phytoestrogens to 118 women for one year, while a control group of 119 women ate biscuits and bars with no soy enrichment. BMD for lumbar spine was assessed at Weeks 1 and 53.

1. the 118 women consuming non-soy enriched biscuits and bars lost 0.70% BMD
2. the 119 women who ate soy enriched biscuits and bars lost 0.71% BMD (Brink E, Coxam V, Robins S, Wahala K, Cassidy A, and F Branca. 2008. Long-term consumption of isoflavone-enriched food does not effect bone mineral density, bone metabolism, or hormonal status in early postmenopausal women: a randomized, double-blind, placebo controlled study. Am J Clin Nutr 87:761-70)

Women who wish to retard bone loss by using soy should be aware of the following negatives of phytoestrogen use:

• Phytoestrogens have been found to affect concentrations of thyroid hormones. (Balmir F, Staack R, Jeffrey E, Jimenez MD, Wang L, and SM Potter. 1996. An extract of soy flour influences serum cholesterol and thyroid hormones in rats and hamsters. J Nutr. 126:3046-53.)

• Phytoestrogens may prevent breast tumor growth or they may promote breast tumor growth. Existing studies have produced conflicting evidence.

Connie Stewart - After many years of dreaming about being a science writer and a book reviewer, Connie is finally exploring both activities as a free-lance ...

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