Hot flushes, night sweats, brain fog? Here's what we know about phytoestrogens for menopausal symptoms

Associate Professor and Clinical Neuropsychologist, Monash University

Senior Research Dietitian in the Department of Gastroenterology, Monash University

Professor of Psychiatry, Monash University

Caroline Gurvich has received funding from the NHMRC, the Rebecca Cooper Foundation and Perpetuel Trustees.

Jane Varney receives funding from the Medical Research Future Fund.

Jayashri Kulkarni receives funding from NHMRC, and has received honoraria from Servier , Janssen, Lundbeck pharmaceutical industries. She has also received two honoraria from Swisse, H&H companies.

Monash University provides funding as a founding partner of The Conversation AU.

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While some women glide through menopause, more than 85% experience one or more unpleasant symptoms, which can impact their physical and mental health, daily activities and quality of life.

Hot flushes and night sweats are the most common of these, affecting 75% of women and the symptom for which most women seek treatment. Others include changes in weight and body composition, skin changes, poor sleep, headaches, joint pain, vaginal dryness, depression and brain fog.

While menopause hormone therapy is the most effective treatment for menopausal symptoms, it is sometimes not recommended (such as following breast cancer, as there is conflicting evidence about the safety of menopause hormone therapy following breast cancer) or avoided by people, who may seek non-hormonal therapies to manage symptoms. In Australia it is estimated more than one-third of women seek complementary or alternative medicines to manage menopausal symptoms.

But do they work? Or are they a waste of time and considerable amounts of money?

The complementary or alternative interventions for menopausal symptoms are almost as varied as the symptoms themselves. They include everything from mind-body practices (hypnosis, cognitive behavioural therapy and meditation) to alternative medicine approaches (traditional Chinese medicine and acupuncture) and natural products (herbal and dietary supplements).

There is some evidence to support the use of hypnosis and cognitive behaviour therapy for the treatment of hot flushes. Indeed these therapies are recommended in clinical treatment guidelines. But there is less certainty around the benefit of other commonly used complementary and alternative medicines, particularly nutritional supplements.

The most popular nutritional supplements for hot flushes are phytoestrogens (or plant estrogens). This trend has been driven in part by supplement companies that promote such agents as a safer or more natural alternative to hormone therapy.

Read more: How long does menopause last? 5 tips for navigating uncertain times

Phytoestrogens are plant-derived substances that can show oestrogen-like activity when ingested.

There are numerous types including isoflavones, coumestans and lignans. These can be consumed in the form of food (from whole soybeans, soy-based foods such as tofu and soy milk, legumes, wholegrains, flaxseeds, fruits and vegetables) and in commercially produced supplements. In the latter category, extracts from soy and red clover yield isoflavones and flaxseed gives us lignans.

Because declining oestrogen levels drive menopausal symptoms, the theory is that consuming a "natural", plant-based substance that acts like oestrogen will provide relief.

In the case of isoflavones, initial support came from epidemiological data showing women in Asian countries, consuming a traditional, phytoestrogen-rich diet (that is, one including tofu, miso and fermented or boiled soybeans), experienced fewer menopausal symptoms than women in Western countries.

However, several factors may influence the effect of dietary phytoestrogens on menopausal symptoms. This includes gut microbiota, with research showing only around 30% of women from Western populations possess the gut microbiota needed to convert isoflavones to their active form, known as equol, compared to an estimated 50–60% of menopausal women from Japanese populations.

Circulating oestrogen levels (which drop considerably during menopause) and the duration of soy intake (longer-term intake being more favourable) may also influence the effect of dietary phytoestrogens on menopausal symptoms.

Overall, evidence regarding the benefit of phytoestrogens for hot flushes is fairly mixed. A Cochrane review synthesised study results and failed to find conclusive evidence phytoestrogens, in food or supplement form, reduced the frequency or severity of hot flushes or night sweats in perimenopausal or postmenopausal women.

The review did note genistein extracts (an isoflavone found in soy and fava beans) may reduce the number of hot flushes experienced by symptomatic, postmenopausal women, though to a lesser extent than hormone therapy.

Another recent study showed marked reductions in hot flushes in women following a low fat, vegan diet supplemented with daily soybeans. However, it was questioned whether concurrent weight loss contributed to this benefit.

In Australia, clinical guidelines do not endorse the routine use of phytoestrogens. Guidelines for the United Kingdom note some support for the benefit of isoflavones, but highlight multiple preparations are available, their safety is uncertain and interactions with other medicines have been reported.

Read more: Is menopause making me put on weight? No, but it's complicated

Less research has explored whether phytoestrogens improve psychological symptoms of menopause, such as depression, anxiety and brain fog.

A recent systematic review and meta-analysis found phytoestrogens reduce depression in post- but not perimenopausal women. Whereas a more recent clinical trial failed to find an improvement.

Some research suggests phytoestrogens may reduce the risk of dementia, but there are no conclusive findings regarding their effect on menopausal brain fog.

At present there is uncertainty about the benefit of phytoestrogens for menopause symptoms.

If you do wish to see if they might work for you, start by including more phytoestrogen-rich foods in your diet. Examples include tempeh, soybeans, tofu, miso, soy milk (from whole soybeans), oats, barley, quinoa, flaxseeds, sesame seeds, sunflower seeds, almonds, chickpeas, lentils, red kidney beans and alfalfa.

Try including one to two serves per day for around three months and monitor symptoms. These are nutritious and good for overall health, irrespective of the effects on menopausal symptoms.

Before you trial any supplements, discuss them first with your doctor (especially if you have a history of breast cancer), monitor your symptoms for around three months, and if there's no improvement, stop taking them.