Nutrition, Education

Soy & Women: Breaking down fact & fiction

Soy & Women: Breaking down fact & fiction

Soy & Women: Breaking down fact & fiction

This article was kindly contributed by Caitlin Adler.
Caitlin is a vegan Accredited Sports Nutritionist and Strength & Conditioning coach at Plant Forged Physique. Her passion is helping vegans achieve their health & fitness goals with evidence-based guidance and expertise. Caitlin is also a competitive IFBB and INBA bikini bodybuilder.


There’s many misconceptions around soy, like claims that soy interrupts female hormones, impacts the thyroid, or even causes cancer. 

This typically comes from claims made about the isoflavones in soy. Isoflavones are a type of phytoestrogen, also known as plant oestrogens. These weakly mimic oestrogen and partially bind to oestrogen receptors.

Isoflavones created concerns that phytoestrogens could alter or have a negative effect on female bodies, like changing hormone levels, or fueling the growth of breast cancer (a hormone-sensitive cancer).

But human trials have proven soy does not increase oestrogen or affect oestrogen-sensitivity. Rather, there’s more research demonstrating the benefits women can experience from consuming soy regularly.


How women can benefit from soy

Breast cancer

An estimated1 in 8 female Australians have a chance of being diagnosed with breast cancer by the age of 85.

Eating soy reduces the risk of breast cancer incidence, recurrence, and mortality. In fact, a 2020 review found that for every 10 mg increase in isoflavone intake (the equivalent of about ~50 g of tofu) per day there was a 3% reduced risk of breast cancer!

Not only that but soy-consuming Asian countries have lower breast cancer rates. For every 100,000 women, breast cancer occurence sits between 25.9-39.2 in Asian nations. Compare that to 94.2 in Australia and New Zealand, or 92.6 in Western Europe.

The reasoning behind this is that isoflavones may block the more potent natural estrogens in the blood on oestrogen sensitive cancers.

Hot flashes

Women will typically experience hot flashes in which they get a sudden warm feeling, skin reddening, and sweating during menopause.Hot flashes occur when decreased oestrogen causes your body to become more sensitive to slight changes in body temperature.

A 2014 review found the consumption of phytoestrogens achieved a greater reduction in hot flush frequency compared to a placebo.

Vaginal dryness and atrophy 

Women may also experience vaginal atrophy during menopause, which is the thinning, drying and inflammation of the vaginal walls that occurs when the body has less oestrogen. It often results in itching, burning or soreness.

Studies into both the effects of a soy-rich diet and applying topical isoflavone creams, saw positive benefits in preventing vagina atrophy and dryness in postmenopausal women.

Bone density

Bone mineral density decreases during menopause which in turn increases the risk of osteoprosis. The annual bone loss is around 0.5% for premenopausal women, compared to, 2% to 2.5% for women going through a pre to post-menopausal transitional, and about 1.5% in postmenopausal women. 

A 2007 review found that isoflavones decreased bone loss in menopausal women. While another 2008 study found that while dietary calcium intake didn’t play an important role in the prevention of bone loss during menopause, the amount of soy in their diet did demonstrate a protective effect on preserving total bone mineral density.


Benefits for men and women

While these benefits are great, there are other benefits that both women and men experience:


Nevertheless, there are two situations in which women may want to be conscious of their soy consumption.

Trying to fall pregnant

There’s mixed research regarding how soy impacts ovulation. Ovulation occurs when the cyclic follicle stimulating hormone (FSH) and luteinizing hormone (LH) are released by the anterior pituitary gland.

Studies on pre-menopausal women have shown mixed changes to FSH and LH – some showing decreases or no changes at all.

However, these studies contained 100-165 mg of isoflavones per day, which is the equivalent of 5-6 servings of soy and much higher than what the average population would consume.

For context, a typical soy-consuming Asian diet includes between 10-25 mg of isoflavones per day, and studies looking at around 50 mg per day have shown little to no impact on circulating levels of reproductive hormones.

Given this, the data suggests that women looking to become pregnant should potentially avoid consuming soy in excess of more than 5 servings or 100 mg soy isoflavones a day, in order to fully optimise their potential to fall pregnant.

Thyroid disease

Thyroid disease affects 10 times more women than men worldwide. And in more recent smaller studies in Australia, around 10% of pregnant women suffer from mild hypothyroidism.  

There were theories that the bioactive isoflavones in soy may affect thyroid function, and influence or worsen thyroid disease. However, review of 14 studies found soy had no impact on thyroid function.

But what it did show is that soy inhibits absorption of the synthetic thyroid hormones found in thyroid medication.

So while soy does not impact the thyroid itself, it does interfere with the absorption of thyroid medication. Those who are taking these medications should consult a doctor before increasing their soy intake, so the dosage can be increased if needed.

Final Thoughts

The controversy around soy consumption can often overshadow its proven benefits. Soy is a great source of protein, calcium, iron, magnesium, zinc and more, and a fantastic food, particularly for vegan and plant-based people.

In addition to this, there are health benefits specific to women, particularly for menopausal women, such as lowering the risk of cancer and lessening symptoms and side effects of menopause like hot flashes, vaginal dryness, and bone mineral loss.

For most people, soy is perfectly fine to consume as much as you please! But there are two instances where soy consumption should be monitored: 

  • If you’re trying to get pregnant, it’s safe to consume less than 5 servings of soy per day.
  • If you are on thyroid medication, it’s worth discussing your soy consumption with your doctor.

But for the majority of people, the research tells us that soy is safe to eat, is beneficial and can be consumed regularly. 

To read more from Caitlin be sure to follow her on Instagram and read more on her website.


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