Understanding Phytoestrogens and Menopause Hot Flashes: A Guide for Dietitians

Vasomotor symptoms (VMS) such as hot flashes and night sweats are among the most common and disruptive experiences for individuals going through menopause.

They typically start in perimenopause and may persist for years after menopause for some. They are not just a mere inconvenience- vasomotor symptoms can impact relationships, work, physical health and emotional wellbeing.

Phytoestrogens, plant-derived compounds with estrogen-like properties, have gained attention as potential nonhormonal interventions for managing these symptoms.

This article will explore:

What causes vasomotor symptoms in menopause
What the current guidelines for the management of vasomotor symptoms
What phytoestrogens are and how they can impact hormones and VMS
The current research on phytoestrogens, their safety and risks, and current guidelines for their use

Understanding Menopause

Menopause is a natural transition every woman and person assigned female at birth (AFAB) will experience. There are over 30 potential symptoms of menopause, with hot flashes and night sweats—referred to as vasomotor symptoms—being the most common. Up to 75–80% of individuals will experience vasomotor symptoms at some point during their menopause journey.

While these symptoms might seem like a mere inconvenience, they can significantly disrupt daily life, affecting relationships, work productivity, self-esteem, and body image.

The Menopause Journey: Key Phases

Menopause Transition (Perimenopause):

The phase can last anywhere between 4 to 10 years. Estrogen levels are declining but can also fluctuate significantly, especially in the later stages.

Early Transition: Initial stage marked by fluctuating menstrual cycles
Late Transition: Hormonal changes intensify, leading to more pronounced symptoms

Menopause:

Defined as the point when an individual has not had a menstrual period for 12 consecutive months. At this stage, the ovaries no longer produce estrogen.

Postmenopause:

Early Postmenopause: The initial years after menopause, when symptoms like vasomotor disturbances may persist
Late Postmenopause: Hormone levels stabilize, and for many, symptoms subside. However, some individuals continue experiencing symptoms well into this phase.

What Are Vasomotor Symptoms?

Vasomotor symptoms, including hot flashes and night sweats, are closely tied to declining estrogen levels.

The exact mechanisms through which estrogen influences hot flashes are complex, involving changes in the body's thermoregulatory processes.

The thermoneutral zone is the range in which a person’s core body temperature is maintained without the need for mechanisms like sweating or shivering. Declining estrogen levels affect the hypothalamus, the brain's temperature regulation center, leading to disruptions in the body’s thermoneutral zone.

In those with vasomotor symptoms, small fluctuations in core temperature can trigger:

Heat Dissipation: Sweating to cool the body
Peripheral Vasodilation: The sensation of sudden warmth, or hot flashes.

Hot Flashes: Characterized by abrupt warmth in the face, neck, and chest, often accompanied by sweating and flushing

Night Sweats: Hot flashes that occur during sleep, frequently disrupting rest and overall quality of life.

Treating Vasomotor Symptoms

Hormonal Interventions

Menopause Hormone Therapy (MHT), also known as Hormone Replacement Therapy (HRT), is the most effective treatment for hot flashes and night sweats.

MHT may lead to a slightly increased risk of blood clots, stroke, or hormone-sensitive cancers in certain individuals. However, recent evidence suggests these risks may be overstated, and for many, the benefits outweigh the risks if MHT is started before the age of 60 and within 10 years of the final menstrual period.

Non-Hormonal Interventions:

For individuals who are not eligible to or would rather not use MHT, several alternatives exist:

SSRIs and SNRIs: Antidepressants that can reduce hot flashes
Gabapentin: Often used for nerve pain but effective in managing hot flashes
Fezolinetant: A neurokinin-3 receptor antagonist that targets the brain’s thermoregulatory centre
Cognitive behavioural therapy: Can help individuals manage and cope with vasomotor symptoms as well as other menopause related symptoms like sleep disturbances

The Role of Diet: Phytoestrogens and Vasomotor Symptoms

Dietary interventions, particularly phytoestrogens, have garnered significant interest in their potential role for managing vasomotor symptoms.

What Are Phytoestrogens ?

Phytoestrogens are plant compounds that mimic estrogen by weakly binding to estrogen receptors, particularly ERβ, which is abundant in bone, urogenital, and brain tissues. These compounds may produce mild estrogenic effects, which could potentially help ease vasomotor symptoms.

There are four main categories of phytoestrogens:

Isoflavones: Found in soybeans, legumes, and red clover
Lignans: Found in flaxseeds, peanuts, berries, tea, and coffee. These are converted by gut microbiota into enterolignans, which may exhibit weak estrogenic activity
Coumestans: Found in small amounts in sprouts like alfalfa
Stilbenes: Found in nuts, broccoli, cabbage, and spinach

Soy Isoflavones

Soy is the richest dietary source of isoflavones, making it a primary focus in research. The most studied forms of soy isoflavones are genistein and daidzein.

In populations with higher soy intake, such as East Asia, where individuals consume on average 30–40 mg or more of soy isoflavones per day, hot flashes are less common than in Western countries, where intake averages less than 1 mg/day.

Not everyone metabolizes soy isoflavones in the same way. Processing and utilization of soy isoflavones in the body depend on the gut microbiome.

S-equol is a metabolite of daidzein, produced by gut bacteria in individuals with specific microbiota capable of the conversion. It has a higher affinity for ER-β compared to daidzein or genistein, making it more effective at mimicking estrogen's effects on bone, cardiovascular health, and the urogenital tract.

Not everyone converts equally:

Only about 20 % of individuals in Western populations and 50-70% in Asian populations are equol producers, due to differences in gut microbiota composition
Factors influencing equol production:
- Diet: High fiber and plant-based diets favor equol-producing bacteria
- Antibiotic use: Previous use may reduce the diversity of equol-producing gut bacteria
- Genetics: Individual genetic variations also play a role in equol metabolism

Soy Isoflavone Research Highlights:

Dietary Soy

One 12-week randomized controlled trial tested a low-fat, vegan diet including ½ cup (86 g) of cooked soybeans daily on 84 postmenopausal women experiencing at least two moderate-to-severe hot flashes daily. Results found:

An 88% reduction in moderate-to-severe hot flashes in the intervention group versus a 34% reduction in the control group.
50% of participants in the intervention group reported no moderate-to-severe hot flashes by the study's end.
Improvements were noted in vasomotor, physical, and sexual quality-of-life domains, measured using the Menopause-Specific Quality of Life questionnaire

This is one of the most cited studies when it comes to the impact of isoflavones on vasomotor symptoms. A few limitations to consider:

This was a relatively small study of only 84 participants
They included women with more than 2 severe hot flashes per day, which is fewer than the 7 to 8 vasomotor symptoms recommended by the US Food and Drug Administration for these types of therapeutic trials. However the researchers did not a sub-group analysis with those who had 7 of more symptoms
The diet was also low fat and vegan, so it is difficult to tease apart whether it was the fat that the diet was vegan, low fat or included soybeans that lead to the improvements

Soy and S-Equol Supplements

The majority of the research is on soy isoflavone supplements.

A systematic review analyzing 15 studies with doses ranging from 40 to 120 mg/day of isoflavones found significant reductions in hot flash frequency compared to placebo. The benefits were particularly pronounced in women taking supplements containing genistein (50-70 mg/day) or S-equol. Supplements containing isolated daidzein were less consistently effective, likely due to variability in conversion to equol.
However, another more recent systematic review of 5 studies found that isoflavones did not have an effect on VMS
Results of S-equol supplements are mixed and inconsistent. Short term and small clinical trials, such as one by this group of researchers, showed that those receiving equol supplements had greater reductions in hot flashes compared to placebo. However, systematic reviews of equol supplementation show inconsistent results. In addition, most of the studies are conducted in Japanese populations who are more likely to be equol producers

Heterogeneity in Research on Soy and Vasomotor Symptoms

The research on soy supplements is highly heterogeneous, with variability in study designs, isoflavone formulations, doses and duration. This makes it challenging to it difficult to draw definitive conclusions amount safety and the optimal dose and duration of soy supplements
Despite some evidence of benefit, the North American Menopause Society (NAMS) does not recommend soy supplements as a primary treatment for VMS, citing inconsistent results and the need for further robust studies.

Safety profile of soy food and supplements

Research shows that dietary soy does not increase breast cancer risk and in fact may reduce risk by up to 11%. Soy consumption in adolescence may offer protective benefits against breast cancer.

While soy supplements appear promising in some studies, one long-term study of 76,442 French women found a higher risk of ER-negative breast cancer in women with a family history of breast cancer who used soy supplements. More research is needed to confirm these findings.

Lignans and Flaxseeds

Lignans are abundant in flaxseeds and are converted by gut microbiota into enterolignans, which may exhibit weak estrogenic activity. However, studies are of variable quality and have shown mixed results, with most studies reporting no statistically significant benefit.

Red Clover

Red clover supplements, containing isoflavones, have shown mixed results in reducing vasomotor symptoms.

Red clover contains isoflavones such as biochanin A and formononetin. Meta-analyses, including one by this group of researchers, reveal moderate reductions in hot flash frequency, particularly in women with severe symptoms and doses of ≥80 mg/day.

However, high heterogeneity across studies limits definitive conclusions. Red clover’s efficacy remains controversial, and more rigorous trials are needed.

Resveratrol

Resveratrol supplementation has shown potential health benefits for postmenopausal women, particularly in improving cognitive function, bone mineral density (BMD), and cerebrovascular responsiveness .

Studies highlight a 10% reduction in overall pain, enhanced cerebrovascular function, and improved flow-mediated dilation (FMD) by up to 35% with long-term use.

Improvements in vasomotor symptoms remain limited and not well-established. Despite its promising effects on pain, cognitive function, and bone health, more robust studies are needed to confirm its direct impact on vasomotor symptoms.

Practical Recommendations for Dietitians

Dietary Strategies

Encourage Soy Intake: Recommend 1–2 servings of soy foods daily, such as tofu, edamame, or soy milk
While flaxseeds do not have consistent evidence, they do offer many other benefits to gut and heart health and can be encouraged as part of a balanced diet
Emphasize a balanced diet rich in whole, plant-based foods
Caution with Supplements: Avoid recommending soy supplements, particularly for individuals with a family history of breast cancer as we do need more research to confirm the safety of these supplements

Healthy Lifestyle Strategies:

Promote regular physical activity to improve overall health and well-being
Encourage stress management techniques, such as mindfulness or yoga, which may indirectly help with vasomotor symptoms

Set Realistic Expectations:

Explain that dietary strategies are complementary, and may not be enough to resolve symptoms
Correct misinformation about dietary soy and breast cancer risk to reduce fear and confusion
Keep up with emerging treatments like Fezolinetant to provide clients with the latest options

Summary of Key Points:

Vasomotor Symptoms include hot flashes and night sweats. They are the most common symptoms during menopause, impacting up to 80% of individuals and significantly affecting quality of life
Menopause Hormone Therapy (MHT) is the most effective treatment for VMS but may not be suitable or desirable for everyone due to risks or personal preferences. Non-hormonal medical interventions and CBT may also used for the management of VMS
Phytoestrogens are plant-based compounds that mimic estrogen by binding to estrogen receptors. Four categories of phytoestrogens include: isoflavones, lignans, coumestans and stilbenes
Soy isoflavones are the most studied. They may help reduce hot flashes, especially in individuals who produce equol, a beneficial metabolite influenced by gut health. However, the research is inconsistent and low quality
Red clover and flaxseeds show mixed efficacy, while resveratrol research on VMS is limited

Conclusion

While the research on phytoestrogens and vasomotor symptoms of menopause is promising, it is far from conclusive.

Dietitians can guide clients toward a phytoestrogen-rich diet while considering individual gut microbiota, dietary preferences, and overall health goals. Education can be provided on the limitations of the research to help patients make an informed decision.