Concerned about soy for PCOS? Soy is an often vilified food group in the PCOS community but does the evidence support the claims that soy is bad for PCOS? In this article we are going to understand what soy is, the link between soy and PCOS, its impact on fertility health and answer your commonly asked questions. Ready? Let’s dive into soy and PCOS.
What is PCOS?
Polycystic ovary syndrome (also known as polycystic ovarian syndrome or PCOS) is an endocrine condition. It is one of the most common hormone disorders and cannot be cured, but instead, PCOS symptoms like hirsutism, oily skin, acne, hair loss on the head and infertility are managed via lifestyle changes like nutrition, exercise, dietary supplements, medication and more.
PCOS is characterised by high insulin, cortisol and testosterone levels.
What is soy?
Soy is a legume native to East Asia. It is widely cultivated for its edible bean. Soy is a rich source of protein and essential amino acids, fibre, omega-3 and omega-6 fatty acids, B vitamins, iron, calcium, magnesium, phosphorus and potassium.
As well as all of those nutrients, soy is rich in compounds called isoflavones (plant-based compounds that have antioxidant properties), phytochemicals and antioxidants.
List of soy foods
Soy can be used to create many soy products including:
1. Tofu – a popular soy product also known as bean curd which is made by coagulating soy milk and pressing the curs into soft, white blocks.
2. Soy milk – a plant-based milk alternative made from whole soybeans or soy protein isolate.
3. Edamame – young, green soybeans still in their pods often served as a snack – this is an unprocessed soy product.
4. Soy sauce – a traditional Asian condiment made by fermenting soybeans, wheat, salt and water.
5. Miso – a Japanese seasoning produced by fermenting soybeans with salt and a type of fungus called koji.
6. Tempeh – a fermented soybean product with a firm texture.
7. Soy nuts – soybeans can be roasted and eaten as a snack or added to other dishes like salads.
8. Soy flour – ground-up soybeans can be used as a flour alternative (particularly if you are gluten-free).
9. Soy oil – a less common household oil that may be used in industrial food production, soy oil is extracted from soybeans.
Benefits of soy
Soy has been traditionally consumed by Asian cultures for centuries. But within the last 21 years soybean consumption in the United States has risen by 4 million metric tonnes as more people enjoy plant-based or vegan diets.
Soy and PCOS: what is the link?
PCOS is an endocrine condition which means it is a hormonal disorder where certain hormones such as cortisol, insulin and sex hormones like FSH, LH, oestrogen and progesterone may not be in their ideal ranges.
As mentioned earlier, soy contains isoflavones which are a type of phytoestrogens. Phytoestrogens are plant-derived compounds that structurally resemble human oestrogen (a female sex hormone). Although phytoestrogens are not identical to oestrogen, they can interact with oestrogen receptors in the body and actually trigger weak oestrogen-like effects. However, it is important to note that isoflavones only have 1/200th of the affinity for oestrogen receptors that actual human oestrogen does so consuming soy is unlikely to impact hormonal balance.
But let’s take a look at what the evidence says about the impact of soy and these plant-based oestrogens on PCOS.
Effects of soy isoflavone supplements on people with PCOS
This first study focused on the effects of soy isoflavone administration rather than the impact of consuming actual soy. This randomised control trial investigated the effect of soy isoflavone supplementation over a three-month period in people living with PCOS. They looked at the effect of daily supplementation of 50 mg of soy isoflavones and found that those who did supplement had lower circulating insulin levels, lower levels of LDL and triglycerides (i.e. improved cholesterol levels), reduced free androgen index and improved insulin resistance and insulin sensitivity compared to the placebo group.
Effect of soy intake on people with PCOS
This next study looked at the effect of actual soy consumption on PCOS patients, rather than supplements. This randomised control trial found that over an eight-week period, those people who had consumed more soy actually had decreased fasting glucose levels, improved insulin sensitivity, decreased fasting insulin and insulin resistance and a decreased free androgen index.
The role of polyphenols in PCOS management
Isoflavones, phenolic acids, flavonols and anthocyanins are all polyphenols present in soy. Polyphenols are a diverse group of naturally occurring compounds found in plants that contribute to the colour, flavour and nutritional properties of many foods and drinks. Interestingly, polyphenols can act as a prebiotic in the gut and the gut bacteria can break down polyphenols to be absorbed and utilised by the body.
PCOS and gut health is an interesting, emerging area of evidence. If soy contains a multitude of polyphenols then soy products may help to improve the health of the gut microbiome which could have benefits for people with PCOS. More research is required, but the link is interesting.
Soy and fertility: helpful or harmful?
How does soy impact fertility? And as soy contains phytoestrogens can they impact hormonal balance and fertility outcomes? Interestingly, the general conclusion on soy and fertility in the literature suggests that soy either improves fertility outcomes or has no effect – very contradictory to the scaremongering you may have seen on soy and fertility online!
Let’s take a closer look at the evidence.
A 2023 review of the epidemiological, clinical and animal data on the effects of soy and phytoestrogen on fertility found that available studies found either no impact or only minor effects of soy intake on fertility. A study of 315 people undergoing assisted reproductive technology found that soy isoflavones intake was positively associated with live birth rates.
Interestingly a 2022 review update found that soy and soy components consumption did not seem to impact fertility and may actually have a favourable effect on those trying to conceive. But, they recognised that the studies included had limited sample sizes and varied study quality highlighting the need for more studies to be completed.
To put it simply, the evidence is varied and more research is required to understand if there is a significant correlation between soy and fertility but soy consumption is unlikely to have a detrimental impact on fertility outcomes.
FAQ: soy and PCOS
If you have any questions about soy and PCOS we’ve summed up the frequently asked questions and provided answers from our team of PCOS nutritionists and dietitians below.
Can soy cause infertility?
Good news – to put it simply, no! Soy cannot cause infertility but more research is needed to understand the effect of soy consumption on fertility.
Is tofu bad for fertility?
Again, soy products like tofu are not bad for fertility. Consuming a varied diet with plenty of nutrients and a balance of macronutrients is more important to focus on if you live with PCOS.
Does eating soy increase oestrogen?
Eating soy is unlikely to increase oestrogen levels because it is a very weak mimic of oestrogen in the human body.
Do I need to take soy supplements?
No, there isn’t enough evidence to suggest that soy supplements will have an effect on PCOS symptoms or fertility. If you are curious about nutritional supplements for PCOS then check out our dedicated article.
Key takeaways: soy and PCOS
To put it simply soy consumption is not something people with PCOS need to be worrying about. If you enjoy consuming soy products and they are a staple in your diet then continue to enjoy your tofu, tempeh and edamame beans. On the other hand, soy is not a wonder food for PCOS and more research is needed to understand its effects on symptoms and fertility outcomes but it does appear to have many other health benefits associated with it.
As always, there is no one PCOS diet and finding a way to eat, move and live that suits you, your symptoms and your lifestyle is essential. We always recommend working with a PCOS nutrition professional for bespoke advice.
Founder and Editor | Registered Associate Nutritionist
Founder of Be The Collective LTD [The PCOS Collective & The Endo Collective] Alex Okell ANutr is a London-based reproductive health nutritionist with experience in research, private practice and digital media. She holds a Master’s degree in Nutrition from King’s College London and has co-authored papers with the University of Cambridge, King’s College London, The Food Foundation and the Food Standards Agency. Alex offers 1:1 PCOS support in our virtual PCOS clinic.