Using Soy Isoflavones for Fertility: How to Take Them and Possible Side Effects

ByRiddhi Roy
Updated:22 Apr 2025, 11:30 am

A group of naturally occurring biochemical compounds called isoflavones present in soy has drawn considerable interest for their seeming ability to modulate hormonal health, particularly in women. These plant compounds, which are also structurally similar to oestrogen, have been heavily researched for their effects on menopausal symptoms, cardiovascular and bone health, and fertility outcomes.

Pregatips.com
Do you have irregular ovulation, or are you simply looking for ways to enhance fertility naturally?
In this article:

Could a simple plant compound from soybeans be the answer to regulating your hormones?
The trend toward natural fertility treatments, and soy isoflavones, is gaining a lot of traction. These plant-based compounds can also have the same effect on the body as oestrogen, thus impacting ovulation and hormonal balance.Originally, soy isoflavones were studied for their impact on menopause, bone health, and cardiovascular function, and now they are being studied for their role in female fertility.

Soy Isoflavones: An Overview

Plant-based compounds called soy isoflavones are phytoestrogens, meaning they mimic the action of oestrogen in the body. The main isoflavones in soy include genistein, daidzein, and glycitein (soy is naturally rich in them, as are soy foods like tofu, tempeh, miso, and soy milk). These compounds bind to oestrogen receptors, emphasised by ER-β receptors and have both mild oestrogen-like and anti-oestrogenic activity. Their activity is mostly reliant on the current hormonal status of the body and the overall endocrine milieu.

Possible Benefits of Soy Isoflavones

Soy isoflavones have been thoroughly investigated in terms of their effects on multiple aspects of health, and researchers have developed both preventive and therapeutic strategies based on this peptide in different populations:
  • Menopausal symptom relief: Isoflavones have been shown to substantially lessen hot flashes and night sweats (vasomotor symptoms) among menopausal women. These phytoestrogens offer a natural alternative to hormone replacement therapy (HRT) for men and women, particularly women who prefer non-synthetic hormone options.
  • Bone health: Declining oestrogen levels put postmenopausal women at risk of developing osteoporosis. Soy isoflavones are suggested to favour the improvement of bone mineral density and markers of decreased bone resorption, thus contributing to lower fracture risk.
  • Cardiovascular health: Consumption of high soy protein and isoflavones has been linked to dose-dependent reductions in LDL cholesterol and triglycerides and improved lipid profiles. However, the beneficial effects of isoflavones on cardiovascular disorders likely stem from their ability to improve endothelial function and lower arterial stiffness.

How Do Soy Isoflavones Affect Fertility?

The interaction of soy isoflavones with the reproductive axis is complex. They can be supportive in particular cases of infertility, but they can also be detrimental in others. The effects depend heavily on someone’s hormonal baseline, dosage of isoflavones, and reproductive goals.

Positive effects

  • Ovulation induction: Soy isoflavones are called clomiphene because they can act as selective oestrogen receptor modulators (SERMs). By blocking oestrogen receptors in the hypothalamus, they trick the body into ramping up the production of follicle-stimulating hormone (FSH) and luteinising hormone (LH), both necessary for maturation and releasing the ovum. This could help women with anovulatory or irregular cycles.
  • Improved ART outcomes: Studies on women undergoing In vitro fertilisation (IVF) or Intrauterine insemination (IUI) have suggested that soy consumption improves fertilisation and even live birth rates. These mechanisms involve increased endometrial receptivity and a balance between cytokines and hormones.
  • Hormonal regulation: Soy isoflavones may provide some mild oestrogenic support in women with low oestrogen levels, particularly those with premature ovarian insufficiency or hypothalamic amenorrhoea. This modulation can also help with more regular menstrual cycles and better follicular development.

Potential risks

  • Disruption of regular cycles: In women with normal endocrine function, high doses of isoflavones may disturb the delicate hypothalamic-pituitary-ovarian (HPO) axis, causing delayed ovulation or abnormal cycle length. Other women have noted longer luteal phases, missed periods, or other menstrual irregularities with extended use.
  • Worsening of hormone-dependent conditions: Women with conditions such as endometriosis, uterine fibroids, or oestrogen receptor-positive breast cancer are generally advised to limit or avoid phytoestrogens. Soy isoflavones have mild oestrogenic activity that may exacerbate these conditions or interact with active hormonal therapies.
  • Thyroid function interference: Isolated soy isoflavones might inhibit thyroid peroxidase. This issue can be particularly concerning for individuals with hypothyroidism or those taking levothyroxine, as it may reduce the effectiveness of their medication and negatively impact their energy levels, weight, or mental clarity.

Who Might Consider Using Soy Isoflavones?

Under appropriate medical supervision, those who may benefit from soy isoflavones include:
  • Women with anovulatory cycles
  • Those actively undergoing assisted reproductive treatments
  • Women who want natural assistance through perimenopause
  • Women who are mildly deficient in oestrogen
However, the appropriate dosage can depend on individual health profiles, which should be comprehensively evaluated before beginning supplementation.

How to Take Soy Isoflavones for Fertility?

While incorporating soy foods into your diet can provide moderate amounts of isoflavones, achieving results for fertility enhancement generally requires standardised supplements. These products deliver concentrated, consistent doses of active compounds (typically 80–200 mg daily) that are difficult to obtain through dietary sources alone. Supplements ensure precise dosing and bioavailability, which is critical for targeting hormonal pathways involved in ovulation and reproductive health. Here is some specific guidance for use:

Dosage

  • The actual dosage depends on the treated condition, but usually ranges between 80 mg and 200 mg per day.
  • Use lower doses (80–100 mg) initially to gauge tolerance and response.
  • Doses greater than 200 mg/day must be given under clinical supervision due to potential adverse alterations in hormone levels.

Timing within the menstrual cycle

  • Fertility protocols recommend taking soy isoflavones for five consecutive days (cycle days 3 to 7 or 5 to 9).
  • These windows match with stimulation during the follicular phase, as you would with a prescription of clomiphene.

Form of administration

  • The most reliable options are capsules or tablets that have been standardised for their isoflavone content.
  • Although soy foods such as tofu and tempeh are healthy, they typically do not supply enough phytoestrogens for therapeutic fertility benefits.

Medical supervision

  • Soy isoflavones are not and never should be a replacement for professional fertility treatment without the approval of a medical professional.
  • Routine hormonal and ultrasound tests may be necessary to monitor their effects.

Side Effects and Risks For Fertility

Soy isoflavones are generally well-tolerated but may cause some side effects in some people. Knowing the potential risks will help you make better decisions:
  • Gastrointestinal problems: Some may feel bloated or nauseous or have light abdominal pain.
  • Headaches and fatigue: These symptoms are typically mild and fleeting but worth noting.
  • Breast tenderness or swelling: If it persists, this may signal oestrogenic action and should be investigated.
  • Hormonal disturbances: Among women with normal menstrual cycles, excessive consumption may inhibit ovulation or cause luteal phase abnormalities.

Who Should Avoid Soy Isoflavones?

  • If you have hormone-sensitive conditions: Have you had a history of breast cancer, fibroids, or endometriosis? Soy isoflavones could, in theory, worsen these conditions due to the mild oestrogen-like effects. You should avoid them unless your healthcare professional clears you.
  • If you’re pregnant or breastfeeding: There is not enough reliable information to say that soy isoflavones are safe to use during pregnancy or breastfeeding. So, to protect your and your baby’s health, it’s best to avoid them completely.
  • If you take certain medicines: Always check with your healthcare professional before taking soy isoflavones, particularly if you take hormonal therapy or antithyroid medication or are undergoing fertility treatments. Your healthcare experts can help determine if supplementation is appropriate.
Soy isoflavones are a unique bridge where nutrition meets endocrinology, potentially serving a dual role in the treatment of a wide spectrum of hormone-related problems, including fertility problems. As phytoestrogens, they can function as either oestrogen agonists or antagonists depending on the individual hormonal environment, with the capability to enhance or inhibit oestrogenic activity. This broader use of them as an adjunct is especially promising in women with ovulatory dysfunction or those receiving assisted reproductive technologies (ART). But their use is not universally appropriate. While soy isoflavones may be an added benefit in certain cases, the nuances of existing medical conditions and individual hormonal profiles need to be considered before implementing them into an individual’s fertility or health plan.

FAQs on Using Soy Isoflavones for Fertility: How to Take Them and Possible Side Effects

  1. Can men take soy isoflavones for fertility?Yes, men can have soy isoflavones, but in moderate amounts. Research indicates that normal dietary intake does not negatively impact testosterone or sperm quality. Yet, too much can alter hormones, and it should be limited.
  2. Are there natural food sources of soy isoflavones?Absolutely. Isoflavones are abundant in edamame, tofu, tempeh, miso and soy milk. These are the best dietary additions, but supplements may need to be taken for therapeutic effects.
Disclaimer: Medically approved by: Dr Sandhya Rani, Sr. Consultant - Obstetrics & Gynaecology, Aster Women & Children Hospital, Bengaluru