A Soy Story: The Controversial Arguments About PCOS and Soy

Ok, so first off a warning: This is a heavily evidence-based article. I’ve been asked often about soy and PCOS and found much of the chatter doesn’t appear to be substantiated. So if you want the nuts and bolts of the research, this article is for you 🙂

Now, let’s jump right in…

Polycystic Ovary Syndrome (PCOS) is surprisingly common among women today, affecting more than 10% of Caucasian women and 15-20% of African American, Hispanic women, and indigenous Australian women. It’s no wonder, then, that the effects of diet and lifestyle on PCOS are often debated – in fact, the rise in unhealthy lifestyles could well be linked to a similar rise in PCOS.  Soy and soy-based products are players in this debate.

With both staunch proponents and passionate objectors of soy, it can be difficult to find an answer to the controversial question – should you include soy in your food plan, or not?


PCOS and soy

What are the potential negatives and the possible positives for PCOS and soy?

Exactly how could soy affect PCOS?

And should PCOS sufferers really stop consuming soy completely?

Polycystic Ovary Syndrome (PCOS)

In order to answer these questions effectively, it is important to understand exactly what PCOS is.

There are three diagnostic criteria for PCOS, of which you need at least two for diagnosis.

1) Polycystic ovaries
2) Increased androgens levels (‘male’ hormones such as testosterone)
3) Irregular or absent periods

(assuming other causes for the signs and symptoms you are experiencing have been ruled out. This is why PCOS is called a diagnosis of exclusion.)

It is worth noting that only around half of the women with polycystic ovaries (PCO) will suffer from Polycystic Ovary Syndrome (PCOS) – PCO and PCOS are not synonymous.

Symptoms of PCOS usually become apparent during the teenage years and can cause a range of issues, including irregular (or even absent) periods, excessive body or facial hair (hirsutism), male pattern balding, infertility, obesity, hot flushes (flashes), sleep apnoea, skin discolouration, fatigue, high blood pressure and mood swings.  PCOS can also lead to more serious illnesses later in life, including type 2 diabetes, heart disease, and certain cancers.


The Joy Of Soy

PCOS and soy… Really?

Soy has many reported benefits. It is a low-cost protein that is a good source of amino acids – perfect for vegans and vegetarians to fulfill their need for this essential nutrient without eating meat.

In 1999, the American FDA released a statement claiming, “diets low in saturated fat and cholesterol that include 25mg of soy protein a day may reduce the risk of heart disease.”  Soy has also been found to help prevent osteoporosis, to lower blood pressure and to alleviate symptoms of menopause and hormone imbalance, as well as generally increasing wellbeing and energy levels.

With such glowing reports on the benefits of soy, surely it would make sense for PCOS sufferers to increase their soy consumption?

But what about its debated effects on oestrogen levels or on thyroid health?

We’ll take a look at these issues shortly.

But first…

What’s In Soy?

Soy contains a significant amount of phytic acid, alpha-linolenic acid, and isoflavones. Let’s take a look at each of these components.

Phytic acid is found not only in soy, but also in foods such as cereal grains, nuts, and seeds.

Phytic Acid – The Cons

“Phytic acid chelates and thus makes unabsorbable certain important minor minerals such as zinc and iron, and to a lesser extent, also macro minerals such as calcium and magnesium.” Nutrients such as these are important for women with PCOS. Studies have found, for example, that PCOS sufferers are more likely to have low levels of magnesium in their blood. And zinc is critical for optimal fertility.

Hurrell et al “concluded that phytic acid is a major inhibitory factor of iron absorption (significantly reduces iron absorption) in soy-protein isolates but that other factors contribute to the poor bioavailability of iron from these products.” Women with PCOS commonly suffer from oestrogen dominance, a sign of which may be menstrual flooding. Flooding may produce an iron deficiency anaemia, in which case it may be helpful to reduce phytic acid intake.

By preparing food rich in phytic acid by cooking methods above 35 degrees Celsius, such as boiling and roasting, as well as soaking and sprouting, this effect can be significantly reduced.

Phytic Acid – The Pros

Heavy metals, such as lead and cadmium, can increase inflammation and reduce insulin sensitivity. These are two main drivers of PCOS. Tsao et al found that “the immobilized phytic acid can absorb heavy metal ions, such as cadmium, copper, lead, nickel” from liquid. This may help to reduce heavy metal toxicity.

Phytic acid has been found to reduce triglyceride levels, act as an antioxidant (important in women with PCOS due to their higher levels of inflammation) and may help to improve gut function by increasing the growth of the ‘good gut bug’ called Bifidobacterium. With gut issues common in women with PCOS, any improvement in gut health may improve insulin sensitivity, reduce high oestrogen levels and increase nutrient absorption.

Excitingly, a study by Thompson et al revealed that adding phytic acid slowed the glycaemic response to legumes. As women with PCOS most often have insulin resistance and need to be careful of foods that raise their blood sugar levels too far, this may be important to note.

Alpha-linolenic acid (ALA)

Alpha-Linolenic acid (ALA) is an essential omega 3 fatty acid. This simply means that the body can’t produce it and so you need to get it from your food plan.

Alpha-Linolenic Acid – The Cons

Alpha-linolenic acid undergoes oxidation more easily than other oils. This means that it ‘goes bad’, or decomposes. This oxidization process will occur when cooked, so foods containing ALA may not be suitable for cooking at higher temperatures. This process can both affect the nutritional content of the food and may potentially create health challenges.

Because of this oxidation, products containing ALA like soybean oil may be partially hydrogenated as this reduces damage and shelf life. The process of partial hydrogenation is not healthful. It produces trans fats, which have been linked to coronary heart disease, raised LDL cholesterol (thought of as ‘bad’ cholesterol) levels and a lowering a HDL cholesterol levels (thought of as ‘good’ cholesterol) (The idea of good and bad cholesterol is not quite accurate, but that debate is for another day).

Alpha-Linolenic Acid – The Pros

Women with PCOS are more likely to suffer from stress, anxiety, fatigue and sleep disorders. A study by Yehuda et al showed that after 3 weeks of supplementing with alpha-linolenic acid and linoleic acid (an unsaturated omega 6 fatty acid), there was significantly reduced anxiety, as well as “better appetite, improved mood, better ability to concentrate, less fatigue during the day, better sleep and (improved) ability to organize themselves.” This author has also previously shown that a mix of alpha-linolenic acid and linoleic acid “improved memory, thermoregulation (temperature regulation) and sleep in humans.”

ALA may also reduce the rate of cancer cell growth. As women with PCOS are at an increased risk of some forms of cancer, this omega 3 fat may provide a valuable and potentially life-saving benefit.  “Taken as a whole, studies suggest that dietary polyunsaturated fatty acids (PUFAs) – including ALA, play a (beneficial) role in cancer risk and progression”. Although the amount needed to have this positive effect may require supplementation, adding ALA-rich foods to the diet may also help.

Women with PCOS are also at an increased risk of heart disease, including further ‘heart attacks’ following their first. A study by de Lorgeril showed that people with increased ALA in their food plan were less likely to have a second heart attack.

We also know that women with PCOS are more likely to suffer from depression. ALA may also be helpful here are well. “A study of over 50,000 women, conducted at Harvard University, over a period of ten years, found that a higher intake of alpha-linolenic acid (combined with a lower intake of linoleic acid) was positively associated with a significant reduction in depression in the same group.”


It is the effects of isoflavones that are often debated in female health and Polycystic Ovary Syndrome. A certain type of isoflavone is known as a phytoestrogen because they can mimic the effect of oestrogen within the body. This is where part of the ‘pro-soy, anti-soy’ arguments lay.

Women with PCOS are often what’s called oestrogen dominant, which means they have either higher relative or total levels of oestrogen in their body and may be more sensitive to the oestrogen that is present.

Phytoestrogens can attach to the oestrogen receptors on cells, meaning they can affect how our body functions. The question is this:

Phytoestrogens are considerably weaker than our own oestrogen. If we increase the amount of phytoestrogens in our food plan, and so in our body, do we add excessive oestrogen to an already overwhelmed system, or do we add a weaker oestrogen that can take the place of at least some of the stronger oestrogen and therefore reduce the oestrogen load?

Let’s look at some research…

Isoflavones – The Cons

A small study on 6 premenopausal women by Cassidy and team found that “soy protein (60 g containing 45 mg isoflavones) given daily for 1 month significantly increased follicular phase length (the first half of your cycle) and/or delayed menstruation.

Mid-cycle surges of luteinizing hormone (LH) and follicle-stimulating hormone were significantly suppressed during dietary intervention with soy protein.”

As women with PCOS already often have low levels of follicle-stimulating hormone (FSH) and often don’t experience the LH surge needed for ovulation, this finding is of concern, as are any delays in menstruation.

Isoflavones – The Pros

Breast cancer is an oestrogen driven cancer. This makes it relevant to discuss in the context of whether phytoestrogens increase or decrease our risk of oestrogen related dis-ease. Do they add to the oestrogen load or reduce it?

Nechuta. S.J. found that “consumption of 10 mg isoflavones per day was associated with a non-significant reduced risk of all-cause and breast cancer-specific mortality (death rate) and a significantly reduced risk of recurrence (of breast cancer).” This would indicate a benefit.

Jayagopal’s study reveals that dietary supplementation with soy phytoestrogens beneficially affected insulin resistance, blood sugar control, and cholesterol levels. This study was performed in women with diabetes, so this is relevant to women with PCOS.

Rivas found that soymilk intake of 500 mL twice daily lowered blood pressure in women with mild to moderate essential hypertension (blood pressure).

A small pilot study in women with PCOS showed that when given 36 mg/d of genistein (a phytoestrogen) for 6 months, the women experienced “improved total cholesterol levels, reducing low-density lipoprotein (LDL) cholesterol and a significant decrease in the LDL–high-density lipoprotein ratio (LDL-HDL). Triglycerides showed a trend toward a decrease.”

These are all great things. There was no change in their menstrual cycle, hormone levels, and body size or insulin resistance.

Yet, in another study by Khani found that “after 3 months of genistein supplement therapy there were no statistically significant differences in high-density lipoprotein cholesterol (HDL) and follicle stimulating hormone (FSH) serum levels in (the) genistein and placebo group before and after treatment; however serum levels of luteinizing hormone (LH), triglyceride (TG), low-density lipoprotein cholesterol (LDL), dehydroepiandrosterone sulfate (DHEAS) and testosterone were significantly decreased after 3 months therapy in Genistein group.

Women with PCOS often have high general levels of luteinizing hormone (LH), which adversely impacts ovulation, and high levels of ‘male’ hormones (dehydroepiandrosterone sulfate (DHEAS) and testosterone). This study would point toward a benefit in women with PCOS including some soy in their food plan to improve many of the challenges these women face.

Soy And Your Thyroid

The thyroid gland (a small gland at the base of the neck) is extremely important. Amongst other functions, it affects the production of follicle stimulating hormone (FSH), and so impacts on ovulation and a regular menstrual cycle.

It is also your energy ‘powerhouse’, and if it doesn’t work well, you may experience weight gain and find it difficult to lose weight, depression, low energy, constipation, infertility, increased risk of miscarriage and more. These signs and symptoms sound a lot like those experienced by women with PCOS, don’t they?  In fact, hypothyroidism (lowered production of the thyroid hormones thyroxin, tri-iodothyronine, and calcitonin) is linked to PCOS and affects many of its sufferers.

This makes it important to know whether soy intake affects thyroid function and if so, how?

In a healthy cycle, there is a surge of luteinizing hormone (LH) and raise in follicle stimulating hormone (FSH) just prior to ovulation. Without this, ovulation does not occur. As women with PCOS often either don’t ovulate or ovulate infrequently, changes to these hormones are important.

A study by Duncan looked at diets which included either a low level or high level of soy (isoflavone) and these hormones…

They found “the low isoflavone diet decreased luteinizing hormone and follicle stimulating hormone levels during the peri-ovulatory phase (the time around ovulation). The high isoflavone diet decreased free T3 thyroid hormone (tri-iodothyronine) and dehydroepiandrosterone sulfate (a weak ‘male’ hormone’) levels during the early follicular phase and estrone levels during the mid-follicular phase. No other significant changes were observed in hormone concentrations or in the length of the menstrual cycle, follicular phase, or luteal phase. Endometrial biopsies performed in the luteal phase of cycle 3 of each diet period revealed no effect of isoflavone consumption on histological dating.”

This suggests that soy may exhibit an unwanted effect on key hormones responsible for ovulation. However, as there was no change in menstrual length or endometrial lining, whether this is biologically and clinically relevant is not clear.

Duncan also found that soy could increase the levels of sex hormone binding globule (SHBG). SHBG is important for reducing the effect of hormones such as the ‘male’ hormone testosterone. Women with PCOS often have high levels of testosterone, which can bring signs and symptoms such as infertility, irregular cycles, acne, excessive hair growth, depression, and anger. Boosting SHBG, often low in PCOS, can have profoundly positive effects.

Research suggests that thyroid cancer may be an oestrogen dependent cancer. Due to this and the debate above about whether soy isoflavones add to oestrogen load or act to reduce it, it is important to ask the question…

What effect do soy isoflavones have, if any, on thyroid cancer?

Horn-Ross revealed “the consumption of traditional and nontraditional soy-based foods and alfalfa sprouts were associated with reduced risk of thyroid cancer. Consumption of “western” foods with added soy flour or soy protein did not affect risk.”

Teas found “soy protein isolate supplementation was not associated with changes in serum thyroid hormone concentrations or thyroid endpoints.” However, they did find that seaweed ingestion did increase serum thyroid stimulating hormone (TSH) levels. (This could be due to the increase iodine seaweed provides; wonderful for the health of the thyroid gland).

A literature review by Messina and Redmond found that there was little evidence that people with a healthy thyroid gland who were not deficient in iodine experienced any adverse thyroid effects from consuming soy foods, or isoflavones. However, women with PCOS often do have hypothyroidism.

There was one case study, which showed soy might inhibit the absorption of thyroid medications in a hypothyroid patient. Although this indicated that soy might change the required dose of thyroid medication, one case study alone is certainly not enough evidence to make broad sweeping recommendations about the effects of soy on thyroid function.

As “there remains a theoretical concern based that in individuals with compromised thyroid function and/or whose iodine intake is marginal soy foods may increase the risk of developing clinical hypothyroidism. Therefore, it is important for soy food consumers to make sure their intake of iodine is adequate.” As iodine deficiency is the worldwide leading cause of hypothyroidism, this is not really surprising.

What About Genetically Modified (GM) Soy?

I don’t like the idea of genetically modified food. This is my personal opinion. There have been arguments about the potential effects, both positive and negative. I have read (debatable) reports showing that GM foods may potentially seriously adversely affect growth and fertility (soy) and have potentially toxic effects (corn).

I have a feeling in my gut that GM is not a positive thing. I don’t like the idea of those with PCOS and soy produced in this way. But can I give you strong, overwhelming evidence to substantiate your avoiding it? No. This is a decision that is for you to make. I feel the best, safest approach is to simply buy Non-GM soy (and other food).

The Amount Of Soy In Modern Day Foods

We are consuming more soy in our foods now than ever before, which we are often unaware of as it is added in traditionally ‘non-soy’ foods. I have concerns about this increase. If we look at gluten, it has been reported that the gluten content in bread has risen from approximately 4% to 17% over a generation. With this rise, we are seeing larger numbers of gluten intolerant people.

Is the same true for soy? This is yet to be seen. The research included in this article has looked into soy components, soy protein isolate and other forms of ‘westernised’ soy, and were not found to have any real health effects. Only time will tell.

So, The Big Controversial Question… Should Women With PCOS Include Soy In Their Food Plan, Or Avoid It Like The Plague?

Despite often-negative press and passionately adverse advocates, the research suggests soy may have benefits for women with PCOS. Consuming soy helps to reduce blood pressure, inflammation, triglyceride levels, anxiety and potentially reduce the risk of breast and thyroid cancer.

It also appears to be helpful in specific PCOS hormonal challenges like reducing oestrogen dominance, reducing ‘male’ hormones, increasing sex hormone binding globule (SHBG), reducing insulin resistance and inflammation and reducing the increased risk of high blood pressure, poor cholesterol balance, diabetes, and heart disease.

A small study indicated that larger amounts of daily soy consumption might reduce triiodothyronine (T3 – the active thyroid hormone).  As T3 is critical in thyroid health, and women with PCOS are more likely to suffer from hypothyroidism, this needs to be considered. However, any theoretical potential effect of soy on thyroid appears to be eliminated by consuming sufficient iodine in one’s food plan.

My Conclusion…

Given the research, I believe that, on current evidence, soy is an important addition to the food plan of women with PCOS. Simply choose organic, ensure a balanced food plan replete with vital nutrients and take a high-quality multi-mineral (which is highly recommended in women with PCOS, regardless of soy intake) and eat in moderation.

From PCOS to perfect health, with love,
Dr. Rebecca Harwin
The PCOS Expert
Nutritionist, Author, Chiropractor

 There is so much being said about soy which is both inaccurate and emotive, so feel free to share this article if you feel it can help.

P.P.S. Like a printable copy of this article? Click on the cover below to download it now.

[1] Harwin, R (Dr.). (2012), Conquer Your PCOS Naturally, Australia: The Publishing Queen. P.19

[2] NHS Choices (2013), Polycystic ovary syndrome, [online]. Available: [13th September 2013]

[3] Ibid.

[4] Ibid.

[5] Harwin, op.cit., pp. 22-23

[6] Medling, A. (2011), To Soy or Not to Soy, [online]. Available: [9th September 2013]

[7] Sexton, J. (2008), Soy: Is It Appropriate for Women with PCOS?, [online]. Available: [9th September 2013]

[8] Zhou J.R.; Fordyce E.J.; Raboy V.; Dickinson D.B.; Wong M.S.; Burns R.A.; Erdman J.W. Jr. (1992), Reduction of phytic acid in soybean products improves zinc bioavailability in rats. [online]. Available:

[9] Hurrell, R.F., Juillerat, M.A.; Reddy, M.B.; Lynch, S.R.; Dassenko, S.A.; Cook, J.D. (1992), Soy protein, phytate, and iron absorption in humans. [online]. Available:

[10] Zheng, Y.; Lu, J.; Gong, C.S. (1997), Adsorption of heavy metal ions by immobilized phytic acid [online]. Available:

[11]Katayama, T. (2005) Reassessment of the nutritional function of phytic acid, with special reference to myo-inositol function. [online]. Available:

[12] Empson, K.L., Labuza, T.P.; Graf, E. (1991) Phytic acid as a food antioxidant. [online]. Available:

[13] Ku, S.M. You, H.J., Ji, G.E. (2009) Enhancement of Anti-tumorigenic Polysaccharide Production, Adhesion, and Branch Formation of Bifidobacterium bifidum BGN4 by Phytic Acid.  [online]. Available:

[14] Thompson L.U.; Button C.L.; Jenkins D.J.A.(1987) Phytic acid and calcium affect the in vitro rate of navy bean starch digestion and blood glucose response in humans. [online]. Available:

[15] Yehuda, S., Rabinovitz. S. , Mostofsky, D.I. (2005). Mixture of essential fatty acids lowers test anxiety. [online]. Available:

[16] Azrad. M., Turgeon. C., Demark-Wahnefried. W. (2013) Current Evidence Linking Polyunsaturated Fatty Acids with Cancer Risk and Progression.  [online]. Available:

[17] de Lorgeril. M., Renaud. S., Salen. P.P., Monjaud. I., Mamelle. N., Martin. J.L., MSc, Guidollet, J., Touboul, P., Delaye. J., (1994) Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease. [online]. Available:

[19] Nicholson, J. (2013), Does Soy Milk Lower Testosterone?, [online]. Available: [13th September 2013]

[20] Cassidy A, Bingham S, Setchell KD. (1994) Biological effects of a diet of soy protein rich in isoflavones on the menstrual cycle of premenopausal women. [online]. Available:

[21] Nechuta SJ, Caan BJ, Chen WY, Lu W, Chen Z, Kwan ML, Flatt SW, Zheng Y, Zheng W, Pierce JP, Shu XO. (2012). Soy food intake after diagnosis of breast cancer and survival: an in-depth analysis of combined evidence from cohort studies of US and Chinese women.

[22] Jayagopal. V., Albertazzi. P., Kilpatrick. E.S., Jennings. P.E., Hepburn. D.A., Atkin. S.A. (2002) Beneficial Effects of Soy Phytoestrogen Intake in Postmenopausal Women With Type 2 Diabetes. [online]. Available:

[23] Rivas. M., Garay. R.P, Escanero. J.F., Petro. C., Cia. P., Alda. J.O. (2002) Soy Milk Lowers Blood Pressure in Men and Women with Mild to Moderate Essential Hypertension. [online]. Available:

[24] Romualdi. D., Costantini. C., Campagna. G., Lanzone. A., Guido. M. (2008) Is there a role for soy isoflavones in the therapeutic approach to polycystic ovary syndrome? Results from a pilot study. [online]. Available:

[25] Khani. B., Mehrabian. F., Eshraghi. A. (2011). Effect of soy phytoestrogen on metabolic and hormonal disturbance of women with polycystic ovary syndrome. [online]. Available:

[26] Harwin, op. cit., pp.149-150

[27] Alison M. Duncan, Barbara E. Merz, Xia Xu, Theodore C. Nagel, William R. Phipps and Mindy S. Kurzer. (1999). Soy Isoflavones Exert Modest Hormonal Effects in Premenopausal Women.

[28] Duncan AM, Underhill KE, Xu X, Lavalleur J, Phipps WR, Kurzer MS. (1999) Modest hormonal effects of soy isoflavones in postmenopausal women. [online]. Available:

[29] Horn-Ross. P.L., Hoggatt K.J., Lee M.M. (2001) Phytoestrogens and Thyroid Cancer Risk

The San Francisco Bay Area Thyroid Cancer Study. [online]. Available:

[30] Teas. J., Braverman. L.E., Kurzer. M.S., Pino. S., Hurley. T.G., Hebert. J.R. (2001) Seaweed and Soy: Companion Foods in Asian Cuisine and Their Effects on Thyroid Function in American Women. [online]. Available:

[31] (Google translator tool needed)

[32] Spiroux de Vendômois. J., Roullier. F., Cellier. D., Séralini. G.E. (2009) A Comparison of the Effects of Three GM Corn Varieties on Mammalian Health. [online]. Available:

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