Soy appears to do nothing to relieve the symptoms of menopause, scientists say, despite the high hopes of many.
A controlled study involving nearly 250 US women going through "the change" found soy tablets did not abate hot flushes or bone density loss.
The tablets were no better than placebo over the two-year-long investigation, Archives of Internal Medicine reports.
But experts said other studies have shown soy can ease menopause symptoms.
The dose given in the latest trial was twice that normally ingested by people with soy-rich diets.
Soy products like tofu contain natural plant oestrogens and experts have suggested that these might help women going through the menopause whose own oestrogen levels are dwindling.
'Not a candidate'
Many women are already offered oestrogen in the form of hormone replacement therapy or HRT to help with menopausal symptoms.
But following reports that prolonged use of HRT may carry a very small increased risk of other conditions, like breast cancer and stroke, some do not want to go on HRT and look for alternatives.
The researchers from the University of Miami say their work suggests soy is not a candidate, although they stress that they only looked at soy isoflavone tablets rather than other dietary sources of soy.
They recruited 248 menopausal women to take part in their study and randomly allocated them to one of two groups: soy or placebo.
The soy group received 200mg of soy isoflavone tablets daily for two years, while the women in the placebo group were given dummy pills.
During the follow-up, no significant differences were found between the two groups regarding changes in bone loss - a common side effect of the menopause.
Menopausal symptoms such as sleep disturbances affected both groups to similar degrees, although the soy group did appear to experience more hot flushes than the placebo group overall.
Lead researcher Dr Silvina Levis said: "My advice would be that women should reconsider taking these products for menopausal symptoms. We found soy isoflavone tablets did not provide any benefit.
"We did not look at soy foods but I suspect these too would probably not be helpful."
Dr Malcolm Whitehead, a menopause expert at King's College Hospital in London, said: "I'm not at all surprised by the findings. In my clinical experience, women say this doesn't work for them."
He said HRT could be a safe and effective treatment for most women.
A spokesperson from the charity Women's Health Concern said that other studies had shown soy could be helpful for treating symptoms of the menopause.