Soy and hot flushes: why it works for her
In brief
There is a documented explanation for why soy relieves some women and not others, and it comes down to a gut bacterium. To act on hot flushes, the daidzein in soy must be turned into equol, something only a particular microbiota can do. In a study of 365 women who regularly ate soy, only 35 % were equol producers. Among them, a high daidzein intake went with far fewer frequent flushes. Among non-producers, no association appeared, whatever the amount of soy eaten.
A friend told you soy changed everything for her hot flushes. You tried it for three months and noticed nothing. You concluded that these products were useless, or that the problem was you.
There is a third explanation, known to research for years and almost entirely absent from consumer content. It has nothing to do with willpower or luck, but with the make-up of your gut flora. This article explains it, then sorts through the other options. It is for information and does not replace the advice of your doctor or gynaecologist.
What happens at menopause
A transition, not a switch
Perimenopause precedes the end of periods and can last several years. Hormone levels fluctuate sharply during it, which is why symptoms are often irregular and disconcerting before they settle. Menopause itself is established after twelve months without a period.
Vasomotor symptoms
Hot flushes and night sweats make up what the literature calls vasomotor symptoms. They are the ones that most affect quality of life, above all through their effect on sleep, and they are what most products sold in pharmacies and online are aimed at.
What this article covers, and does not
We are talking here about nutrition and food supplements. Menopausal hormone therapy is a medical option in its own right, whose indication, benefits and risks are discussed with a doctor. No supplement takes its place, and none treats menopause, which is not a disease in any case.
The equol story, or why the studies contradict each other
The mechanism
Soy contains isoflavones, the main one being daidzein. That molecule is not the most active: it is its conversion by certain gut bacteria into another molecule, equol, that produces the effect sought on vasomotor symptoms. Without the right bacteria, the conversion does not happen.
An ability not everyone has
This is the central point: that conversion ability is present in a minority of people in the West. In the study detailed below, involving women who nonetheless ate soy at least three times a week, 129 out of 365, or 35 %, were equol producers[1].
What the trials show as a whole
A meta-analysis brought together 15 randomised trials on phytoestrogens in perimenopausal or postmenopausal women, with interventions lasting 3 to 12 months. Its result has two parts, and deserves precise reading: on the frequency of hot flushes, phytoestrogens do significantly better than placebo; on the overall menopausal symptom score, by contrast, no significant difference appears[2]. On tolerability, no difference in adverse effects was seen compared with placebo.
In other words, the effect exists and is measurable, but it is targeted: it bears on the number of flushes, not on the whole picture. That is exactly the kind of benefit to expect, no more and no less.
What this explains
It clears up at a stroke the contradictory results of trials on isoflavones. A study recruiting mostly non-producers will find no effect; another with more producers will find one. Without measuring that status, the two appear to contradict each other, when in fact they are measuring two biologically different populations.
The figures, and what they allow us to say
The protocol
Three hundred and sixty-five women aged 45 to 55, menopausal or in transition, eating at least three portions of soy a week, kept a diary of their flushes for three days and provided a 24-hour urine collection allowing their equol production to be measured[1].
The result
Among equol producers, those with the highest daidzein intake, around 28 mg a day, had a 76 % lower risk of having an above-average number of flushes, compared with those whose intake was lowest, around 5 mg a day. Among non-producers, no association appeared between daidzein intake and the frequency of flushes[1].
The limits, plainly stated
This is a cross-sectional study, that is, a snapshot at one moment: it shows an association, it does not demonstrate cause and effect. The intensity and bother reported did not, moreover, differ by intake, only the number of flushes was affected. Finally, several authors are affiliated with companies in the sector, which is part of the picture[1].
| Group | High daidzein intake |
|---|---|
| Equol producers (35 % of participants) | 76 % lower risk of frequent flushes |
| Non-producers (65 %) | No association observed |
| Reported intensity and bother | No difference in either group |
The other options, without indulgence
Black cohosh
It is the best-selling plant in this area. Trial results are heterogeneous, and above all cases of liver injury have been reported, which has led several authorities to require a warning statement. Its use should be discussed with a professional, particularly in case of liver disease or a treatment under way.
Products marketed as natural
That a product is of plant origin says nothing about its safety or its effectiveness, as the previous example shows. The useful rule is the same as everywhere else: ask which study, in which population, at what dose, and who funded it.
What has not proven itself
Many formulas combine a dozen extracts at low doses, without any of them having been assessed in that composition. Piling up ingredients is no guarantee of effectiveness: on the contrary, it makes it impossible to know what is acting, and complicates identifying an adverse effect.
What weighs at least as much as supplements
Muscle strength
Falling oestrogen speeds up the loss of muscle and bone. Resistance training acts on both at once, which no capsule does. It is the intervention with the best benefit-to-effort ratio at this stage of life, and it can be built up gradually, at any age.
Protein
Sufficient protein intake becomes more important when muscle is harder to hold on to. Spread across meals rather than concentrated in the evening, it supports the muscle work being done. Protein contributes to the growth and maintenance of muscle mass and to the maintenance of normal bones.
Sleep and alcohol
Night sweats fragment sleep, and the resulting fatigue amplifies the perception of every other symptom. Cutting back on alcohol, particularly in the evening, is one of the most rewarding measures: it disturbs sleep architecture and triggers flushes in many women.
When to see a doctor
The situations that warrant advice
Symptoms clearly affecting quality of life, lastingly poor sleep, bleeding after menopause, pain during sex, or simply the wish to consider hormone therapy: all of these belong in a consultation, not in an online purchase.
What is useful to bring
A record of your symptoms over two to three weeks, the full list of what you take, supplements included, and your personal and family history. That makes the consultation considerably more effective, particularly for weighing the benefits and risks of a treatment.
The lesson of this file goes beyond menopause. A product can be effective in only part of the population, for an identifiable biological reason, here the microbiota’s ability to produce equol. Not knowing that variable turns a difference in response into a misunderstanding, and has people buying months of supplements they cannot benefit from.
To go further, two articles complement this one: our file on gut flora, which plays an unexpected role here, and the one on hypothyroidism, whose symptoms are often confused with those of perimenopause.
Frequently asked questions
Why does soy relieve some women and not others?
Because the daidzein in soy has to be turned into equol by gut bacteria in order to act on flushes, and not every woman has that microbiota. In a study of 365 women who ate soy at least three times a week, only 35 % were equol producers. Among them, a high daidzein intake went with a 76 % lower risk of frequent flushes; among the others, no association at all.
Can you find out whether you produce equol?
It can be measured in urine after eating soy, as in the study cited, but this test is not a routine investigation and its practical value remains limited outside research. A simpler approach is to note your symptoms over a few weeks of regular dietary soy: if nothing changes, pushing on with higher doses is unlikely to alter the picture.
How much soy should you eat?
In the study, participants in the top quartile took in around 28 mg of daidzein a day, against about 5 mg for the lowest quartile, and all ate soy at least three times a week. These figures describe an observed association, not a recommended dose. Dietary soy remains the simplest route, and any supplementation is discussed with a doctor.
Are isoflavones safe?
They are molecules with activity close to that of oestrogens, which calls for caution. Their use must be discussed with a doctor in case of a history of breast cancer or another hormone-dependent cancer, and where a treatment is under way. As with any supplement, mention them in consultation. A food supplement neither treats nor prevents any disease.
What is black cohosh worth?
It is the best-selling plant in this area, but trial results are heterogeneous and cases of liver injury have been reported, leading several authorities to require a warning. Its use should be discussed with a professional, particularly in case of liver disease or a treatment under way. That a product is of plant origin says nothing about its safety.
Do supplements replace hormone therapy?
No. Menopausal hormone therapy is a medical option in its own right, whose indication, benefits and risks are weighed individually with a doctor. No food supplement takes its place, and none may legally claim to. If your symptoms clearly affect your quality of life, a consultation is the most useful step.
What helps besides supplements?
Two levers stand out. Resistance training acts on both muscle mass and bone, two tissues weakened by falling oestrogen, which no capsule does. And cutting back on alcohol, particularly in the evening, often improves things markedly: it disturbs sleep architecture and triggers flushes in many women.
Perimenopause or something else?
The question is worth asking, because several situations produce similar symptoms, in particular thyroid disorders and iron deficiency, both common at this age. Fatigue, sleep problems, mood changes and weight gain are not specific. Testing makes it possible to rule out these causes rather than attributing every symptom by default to the hormonal transition.
Sources and references (verified on PubMed)
2 sources- Newton K.M., Reed S.D., Uchiyama S., Qu C., Ueno T., Iwashita S., Gunderson G., Fuller S., Lampe J.W. (2015). A cross-sectional study of equol producer status and self-reported vasomotor symptoms.
- Chen M.-N., Lin C.-C., Liu C.-F. (2015). Efficacy of phytoestrogens for menopausal symptoms: a meta-analysis and systematic review.