Soy and isoflavones for menopause: hot flashes, bones and safety

Name: Soy and isoflavones for menopause: hot flashes, bones and safety
Creator: MenoWoman

Soy isoflavones are plant compounds with a structure similar to estrogen. They may reduce hot flashes slightly in some women, but trial results are mixed, and The Menopause Society does not recommend them.

Researched by the MenoWoman team. Edited by Marcela Sat. Updated 7 November 2026. We may earn from links.

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See a doctor if hot flashes disrupt your life, if you have had a hormone-sensitive cancer, or if you have any vaginal bleeding after menopause.

What it is

Soy comes from soybeans. It is found in foods like tofu, soy milk, tempeh and edamame. Soy contains isoflavones, a type of plant estrogen (phytoestrogen).¹

Isoflavones are shaped like the hormone estrogen. This is why people hope they might ease menopause symptoms. They are sold as concentrated supplements as well as eaten in food.¹

Some women's gut bacteria turn a soy isoflavone into a compound called equol. Only about 35% of North American women can do this, and testing is not commercially available.³

What the research shows

A Cochrane review in 2013 looked at 43 trials with 4,364 women. It found no conclusive evidence that phytoestrogen supplements reduce hot flashes or night sweats.²

Some soy trials showed a benefit, but many were small and at high risk of bias. Four trials of high-strength genistein, one soy isoflavone, did reduce hot flashes. The authors said genistein needs more study.²

The NIH center for complementary health says soy may reduce hot flashes a little. It adds that the effect may be small and results are not consistent.¹

The Menopause Society reviewed the evidence in 2023. It called the evidence mixed and does not recommend soy foods, soy extracts or equol for hot flashes.⁴ Many trials were short, small and used different products.³

For bones, the NIH center says soy isoflavones probably help bone density in postmenopausal women.¹

Safety and who should be careful

Soy is safe as a food for most people. Soy is one of the most common food allergens. Reactions range from mild to life-threatening.³

Side effects of supplements can include bloating, constipation, diarrhea and nausea. Isoflavone extracts have been studied safely for up to 6 months.¹ The Cochrane review found no sign that they stimulated the womb lining over up to 2 years.² But one Italian trial gave high-dose isoflavone tablets or placebo to 376 women for 5 years. About 3% on isoflavones developed thickening of the womb lining, compared with none on placebo.⁵ So long-term high-dose use is not known to be safe.

In Asian and Asian-American women, eating more soy is linked with a lower breast cancer risk. Supplements have not been shown to lower breast cancer risk.¹

Because isoflavones resemble estrogen, women who have had breast cancer or another hormone-sensitive condition should talk to their cancer team or doctor before taking supplements.

Some soy foods, like tofu and soy sauce, are high in tyramine. Tyramine can react with a type of antidepressant called MAO inhibitors and cause a dangerous rise in blood pressure.¹

Soy may make it harder for the body to absorb thyroid hormone medicine (levothyroxine).⁶ A doctor or pharmacist can advise on this, and can check for interactions with any other medicines or supplements you take.

How it is available

Soy foods are sold widely around the world. Isoflavone supplements are sold over the counter in many countries, often from soy or red clover. Products differ in their type and amount of isoflavones, which makes them hard to compare.³

The bottom line

Eating soy foods as part of a balanced diet is safe for most women. Any effect on hot flashes is likely to be small, and it varies a lot between studies.^1,2

Placebo effects in these trials were large, cutting hot flashes by up to 59% in some.² This makes it hard to know how much soy itself adds.

For stronger options, see hormone therapy and non-hormonal prescription treatments.

What it is used for: evidence rated

Option	Evidence	What the research shows
Bone loss	Some evidence	The NIH center says soy isoflavones probably help bone density after menopause.¹
Hot flashes	Weak evidence	Results are mixed; a Cochrane review of 43 trials found no conclusive benefit, though high-strength genistein trials looked better.²
Night sweats	Weak evidence	Included in the same reviews, with no conclusive evidence of benefit.²

Ratings explained: how we rate. Always talk to a doctor or pharmacist before starting a medicine or supplement.