The study, published in JAMA’s Archives of Internal Medicine, reports that soy isoflavone tablets are not associated with a reduction in bone loss or menopausal symptoms in women within the first five years of menopause, and may actually lead to an increase in certain menopause symptoms such as hot flushes and constipation.
“Because of concerns regarding the risk of estrogens, a need exists for alternative interventions that could provide the beneficial effects of estrogens in bone and menopausal symptoms without the adverse effects on breast and cardiovascular health,” said the authors, led by Dr Silvina Levis from the Miami Veterans Affairs Healthcare System and Miller School of Medicine, at the University of Miami
“In this population, the daily administration of tablets containing 200 mg of soy isoflavones for 2 years did not prevent bone loss or menopausal symptoms,” they added.
Levis and her colleagues explained that the beginning stages of menopause are often accompanied by rapid bone loss, hot flushes, vaginal dryness and sleep disturbances among other symptoms.
“Estrogen therapy with or without progesterone prevents most of these changes. However, as a result of the Women's Health Initiative findings suggesting that the overall risks outweigh the benefits, most menopausal women now decline estrogen therapy, increasingly seeking other alternatives,” said the authors.
“Soy-derived products have been proposed to provide comparable benefits to estrogens but without the risks,” they said.
The authors explained that previous epidemiologic and prospective studies of Asian women consuming a typical high-soy Asian diet, suggest a beneficial skeletal effect of soy foods.
“On the basis of this information, Western women have significantly increased their consumption of soy products in the past decade,” said Levis and her team.
Soy proteins are known to contain phytoestrogens (specifically the isoflavones genistein and daidzein), which are able to bind to the estrogen receptors and can elicit a weak responses.
Levis and her team conducted the randomized controlled trial over a five year period between 2004 and 2009 to determine the effectiveness of soy isoflavone tablets in preventing bone loss and other menopausal symptoms.
The researchers recruited a total of 248 women for the study; 126 were randomized to the group receiving placebo tablets and 122 were randomized to receive a soy isoflavone dose of 200 mg per day – a dose equivalent to approximately two times the highest intake through food sources in a typical Asian diet to ensure they received an effective dose
Levis and her co-workers reported that during two years of follow-up, no significant differences were found between women in the soy isoflavone group and placebo group regarding changes in bone mineral density of the spine, the total hip, or the femoral neck.
The researchers did however that “a significantly larger proportion of participants in the soy group experienced hot flashes and constipation compared with the control group.”
“We found that 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,” said Levis and her team.
Earlier this month, the final batch of the European Food Safety Authority’s general function, article 13 health claims opinions included a rejection for the ability of soy isoflavones to affect a number of health conditions including menopause, reducing LDL cholesterol and to deliver antioxidant benefits.
At the time, health claims expert Nigel Baldwin, from Intertek-owned Cantox International, said he was not surprised by the soy opinion that rejected soy isoflavones’ ability to reduce menopausal symptoms, lower LDL blood cholesterol levels and act as an antioxidant.
“That one was always far too complex to be covered by Article 13.1 so no surprises there,” he said. “The claims are controversial with some experts anyway so a really thorough dossier was what was needed.”
EFSA's soy opinion can be found here.
Source: Archives of Internal Medicine
Volume 171, Issue 15, Pages1363-1369, doi:10.1001/archinternmed.2011.330
“Soy Isoflavones in the Prevention of Menopausal Bone Loss and Menopausal Symptoms: A Randomized, Double-blind Trial”
Authors: S. Levis, N. Strickman-Stein, P. Ganjei-Azar, P. Xu, D.R. Doerge, J. Krischer