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OtherModerate evidence

Soy isoflavones

Also known as: genistein, daidzein, phytoestrogens

Soy isoflavones (genistein, daidzein, glycitein) are plant compounds with weak oestrogen-like activity, found in soy and soy foods. They are used mainly to ease hot flushes in menopause.

What it is used for

  • easing menopausal hot flushes – moderate evidence, the effect is modest and slow to appear
  • bone density after menopause – weak to moderate evidence, mixed results
  • cholesterol support (soy as a food) – weak evidence

Forms and how they differ

soy extract

isoflavone content is given in mg per serving – check the label

fermented forms (aglycones) and S-equol

may work better in people who do not produce equol; evidence is limited

soy foods (tofu, tempeh, soy milk)

natural source of isoflavones with protein

When to take it

With food, split through the day; the effect is judged after 2–3 months.

Pairs well with

Calcium, vitamin D, a fibre-rich diet (gut bacteria convert daidzein into equol).

Do not combine / separate

Keep at least 4 hours apart from thyroid medication (levothyroxine). Take care with blood thinners (warfarin) and hormone therapy.

Watch out for

With a history of breast or uterine cancer, hormone-sensitive conditions or thyroid disease, consult your doctor. Not suitable in pregnancy or breastfeeding; if you take medicines, consult your doctor.

Safety

EFSA did not conclude harm at the doses studied in postmenopausal women, but long-term data are limited; do not exceed the label dose.

Practical tip

If you eat soy foods regularly, count them towards your total isoflavone intake.

Products containing Soy isoflavones 1

Soy isoflavonesextractWomen’s healthHormonesBones
How to read the evidence rating
Strong evidenceModerate evidenceWeak evidenceNo evidence

Strong = several good human studies or official recommendations; moderate = promising but smaller studies; weak = few studies or mixed results; no evidence = claims not confirmed.

Combination check

Select the supplements you take and, if relevant, your medicines. We show what interferes, what needs a time gap and what to watch out for.

Check Soy isoflavones with others

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From the same group

AlfalfaNo evidenceAndrographisWeak evidenceAroniaWeak evidenceBarley grassWeak evidenceBee pollenWeak evidenceBeef organs (desiccated)Weak evidence
Important notice

This information is educational and does not replace advice from a doctor or pharmacist. We do not give medicine dosages. Supplements are no substitute for a varied diet; if pregnant, breastfeeding, ill or on medication, consult a doctor first.