Soy and PCOS: Safe or Harmful?

One of the most controversial topics regarding nutrition and PCOS is
soy. Both The American Dietetic Association and the FDA say that soy
is safe. In fact, there is a food claim approved by the FDA stating that
"diets low in saturated fat and cholesterol that include 25 grams of soy
protein a day may reduce the risk of heart disease". Proposed benefits
of soy include improved cholesterol, decreased risk of cancer, and
improved menopausal symptoms among others. Yet, if you do an
internet search for PCOS and soy and you will see many people
confused about it, with some saying that soy is terrible for PCOS and
should be avoided at all costs. Some claims against soy imply that soy
is detrimental to the health of humans as it may cause cancer, nutrient
deficiencies, osteoporosis, thyroid problems, reproductive difficulties,
and Alzheimer's Disease. This article explores some of the
controversies surrounding soy as it applies to PCOS.

What is soy?

Soy is a plant food that is also a complete protein, meaning it has all
required amino acids. It is also low in fat, contains essential fatty
acids, numerous vitamins, minerals, and fiber. Soy foods include soy
milk and cheese, tofu, tempeh, miso, soy sauce, and edamame.
Another form of soy, soy protein isolate, is often added to energy and
granola bars and meat-alternative products. Soy protein isolate may
contriubute to estrogen dominance commonly seen in PCOS.

Evaluating the research

Soy is one of the most widely researched foods around. It is even
being grown in space! Not all the research surrounding soy is positive.
There are many claims that soy is harmful, especially for women with
PCOS. As a nutrition expert, it is my job to provide reliable and
objective nutrition information. I can't just rely on one or two studies
to base my recommendations on. I have to look at the whole picture.
There are some studies available that do show adverse effects of soy.
Most of this evidence, however, is based on animal studies and
involves a much higher amount of soy than most humans typically
consume. Keep in mind soy is not estrogen and does not act the same.
The power of soy is extremely weak when compared with estrogen.
Currently, there are very few studies done that actually look at PCOS
and soy intake. One study shows favorable results for PCOS in
improving cholesterol (1). On the other hand, there are many studies
(again, most of them involve rats) available showing that soy intake
can affect fertility, in which case some women with PCOS may prefer
to limit it.

Soy and hypothyroid

Some studies associate soy intake with hypothyroidism, a condition
that many women with PCOS have. Soy foods contain isoflavones
called genistein and diadzien (also found in some certain foods such as
some whole grains and legumes). Generally these isoflavones only
cause problems in areas where iodine intake is low (iodine is an
important mineral for thyroid function) (2-4). Individuals who do
consume a healthy diet and have an adequate iodine intake (milk and
fish are rich in iodine), probably won't be affected by a moderate
amount of soy products in their diet. Those individuals who eat a poor
diet or consume a low calorie diet and are deficient in iodine may
experience thyroid disturbances from eating soy. If you suffer from
hypothyroid you may want to limit your soy intake. If you don't have
hypothyroid and enjoy eating soy products, you should have your
thyroid levels checked yearly as a precaution.

Soy and cholesterol

Many women with PCOS have elevated cholesterol levels. This is
dangerous as it can lead to cardiovascular disease. Limiting the
consumption of saturated fat (often found in animal products) is one
way of reducing cholesterol. A moderate intake of soy can then be
used as a substitute for products containing saturated fat (for
example, tofu used in stir fry instead of beef). One study revealed that
administration of soy in women with PCOS not only reduced LDL
cholesterol but also significantly reduced LH, TG, DHEAS and
testosterone parameters after 3 months. In another study,twelve
obese women with PCOS who had high insulin and high cholesterol
consumed 36 grams of soy each day for 6 months. The results showed
favorable improvement in reducing LDL cholesterol (the bad type).
There was no affect on weight loss, hormones, or menstrual cycle in
this study (1).

Soy and infertility

It is currently unknown whether soy has a positive or adverse effect on
the fertility in women with PCOS. As mentioned, hardly any studies
exist involving soy with PCOS and none so far have really examined its
affect on ovulation. A recent large study showed showed that for high intake of soy isoflavones (over 40 mg/day), the lifetime risk of never becoming pregnant increased by 13% and that of ever giving birth to a live child was reduced by approximately 3%.

One study found that 6 g/day of black soybeanpowder taken for 6 months improved ovulation in women who weren't ovulating (5). On the other hand, there are many studies available that show that mice treated with genistein had reduced fertility (6).Some studies even suggest early exposure to soy and/or isoflavones like those found in soy-based infant formulas may have long-term
effects on reproduction (4).

A study in The Journal of the American Medical Association, however, found no difference in a wide range of reproductive problems between those who were fed soy formula and those fed cow
milk formula as infants (8). A review of 7 soy intervention studies done on women using 32-200 mg/day of isoflavones showed increased menstrual cycle length (9).

Currently the evidence doesn't imply that soy prevents ovulation but may delay it. While much more research is needed, those of you who are trying to become pregnant or struggle with infertility may want to
limit your intake of soy.

Bottom line: More studies need to be conducted on soy consumption as it applies to humans, and with PCOS in particular. Soy in the form of soy protein isolate should be avoided for all women with PCOS.
Women with PCOS who struggle with infertility, hypothyroidism, consume few calories or eat a poor diet may want to avoid or limit soy products.Otherwise, a moderate-low intake of organic, non-GMO soy products (once a day or few times a week) can be part of a healthy diet for women with PCOS. For a listing of mg of soy foods, click here.


1. Romualdi D, Costantini B, Campagna G, Lanzone A, Guido M.Is there a role for soy
isoflavones in the therapeutic approach to polycystic ovary syndrome? Results from a pilot study.
Fertil Sterility. 2007.
2. Duncan AM, Underhill KE, Xu X, Lavalleur J, Phipps WR, Kurzer MS. Modest hormonal effects
of soy isoflavones in postmenopausal women. J Clin Endocrinol Metab 1999; 84:3479-84.
3. Duncan AM, Merz BE, Xu X, Nagel TC, Phipps WR, Kurzer MS. Soy isoflavones exert modest
hormonal effects in premenopausal women. J Clin Endocrinol Metab 1999; 84:192
4. Bruce B, Spiller GA, Holloway L. Soy isoflavones do not have an antithyroid effect in
postmenopausal womem over 64 years of age. Faseb J 2000; 11:193 (abstract).
5. Kohama T. The Effect of soybeans on the anovulatory cycle. J Med Food. 2005;8(4): 550-551.
6 Jefferson WN, Padilla-Banks E, Newbold RR. Disruption of the developing female reproductive
system by phytoestrogens: genistein as an example. Mol Nutr Food Res. 2007;51(7):832-44.
7. Mendez MA, Anthony MS, Arab L. Soy-based formulae and infant growth and development: a
review. J Nutr. 2002;132(8):2127-30.
8. Strom BL, Schinnar R, Ziegler EE, et al. Exposure to soy-based formula in infancy and
endocrinological and reproductive outcomes in young adulthood. JAMA. 2001; 286:807-14.
9. Kurzer MS. Hormonal effects of soy in premenopausal women and men. J Nutr 2002;
10.Bjarne K Jacobsen,1 Karen Jaceldo-Siegl,2 Synnøve F Knutsen,2 Jing Fan,2 Keiji Oda,2 and Gary E Fraser2. Soy isoflavone intake and the likelihood of ever becoming a mother: the Adventist Health Study-2 Int J Womens Health. 2014; 6: 377–384.

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