Phytoestrogens: miracle cure or hype?

Phytoestrogens are plant-based compounds that resemble the hormone oestrogen in structure. The two best-known groups are isoflavones, primarily found in soy, and lignans, which are present in flaxseed, whole grains, and legumes, among other foods.

Although they are structurally similar to oestrogen, phytoestrogens do not function in the same way as the hormone produced by the body. Their effect is much weaker and depends on factors such as the type of phytoestrogen and how the body processes it.

Oestrogen exerts its effects by binding to oestrogen receptors in various parts of the body. Phytoestrogens can also bind to these receptors, but they do so less strongly and not uniformly.

Depending on the circumstances, phytoestrogens can mildly mimic the effects of oestrogen or, conversely, weaken them. The strength of this effect varies depending on the specific compound and its location in the body. This makes their action more complex than standard oestrogen replacement therapy.

Phytoestrogens can be obtained through diet, for example, by consuming tofu, soy milk, flaxseed, legumes, and whole grains. Hops and red clover are also sources of phytoestrogenic compounds.

There are also supplements containing, for instance, soy isoflavones or red clover extract. The effectiveness of these supplements can vary from one woman to another, possibly due to differences in gut microbiota. In some women, gut bacteria convert daidzein, an isoflavone found in soy, into equol. Equol binds more strongly to certain oestrogen receptors than daidzein. However, not everyone can produce equol, which may explain why some women experience greater benefits from soy isoflavones than others.

Because phytoestrogens can interact with oestrogen receptors, researchers have studied whether they can alleviate symptoms such as hot flushes and night sweats. Various studies have yielded intriguing results, although the findings are not always consistent.

In one study involving 60 women, participants received either 60 mg of soy isoflavones daily or a placebo for twelve weeks. Of the 60 women, 51 completed the study. Among those who took isoflavones, hot flushes decreased by 57% and night sweats by 43%. This represents a significant improvement within this group, although it was a relatively small study.

A second study, involving 96 women, sheds light on why the effects may differ among individuals. Researchers examined the ability to produce equol from soy isoflavones. In women who could produce equol, hot flushes and excessive sweating decreased after three months compared with the placebo group. After six months, other symptoms, such as palpitations and tingling in the arms and legs, also improved in this group. However, these effects were not observed in women who could not produce equol.

A larger study also reported positive results. Of the 192 women who participated, the researchers assessed the number of hot flushes in 136 women. After twelve weeks, the number of hot flushes decreased by 43.3% with soy germ extract, compared with 30.8% in the placebo group. While soy appears to offer some benefit, the difference from the placebo group is smaller than the percentages might initially suggest.

The results of these studies are promising, but when researchers analyse multiple studies collectively, a more nuanced picture emerges. A 2025 analysis found no definitive effect of soy isoflavones on hot flushes. However, a 2026 review indicated that soy-containing foods might help reduce hot flushes, though the evidence was weak.

Thus, there are indications that soy may provide relief for some women, but the effect has not been conclusively demonstrated. Further research is needed to determine who might benefit and under what conditions.

There is a distinction between phytoestrogens obtained through a regular diet and those from supplements containing concentrated doses. Soy products generally fit well within a healthy diet, even for women who have had breast cancer. However, caution is advised with supplements, which often contain much higher concentrations of isoflavones than food. The safety of long-term use and use in hormone-sensitive conditions is less well understood.

If you have had breast cancer or another hormone-sensitive condition, or if you are taking medication, it is advisable to consult your doctor or pharmacist before using phytoestrogen supplements.

In my opinion, phytoestrogens are not a miracle cure, but they are not mere hype either. Some women experience fewer hot flushes or less night sweating, while others notice little to no difference. Research does not yet provide a clear and consistent picture.

We still do not fully understand why some women benefit more than others. The gut microbiota appears to play a role, but other factors are likely involved as well.

My advice is to first consider whether taking a supplement is appropriate for your situation. If you decide to try it, evaluate after approximately eight to twelve weeks whether you notice any improvement. This allows sufficient time to assess its effectiveness without assuming it will work for everyone.