Soy and PCOS: Safe or Harmful?

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.

There are many claims that soy is harmful, especially for women with PCOS.
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.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 avoid 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). A recent and small study examined the use of soy with women with PCOS (1). 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. One study found that 6 g/day of black soybean powder 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: much more studies need to be conducted on soy consumption as it applies to humans, and with PCOS in particular. Women with PCOS who struggle with infertility, consume few calories or eat a poor diet may want to avoid or limit soy products. Otherwise, a moderate-low intake of soy (once a day or several times a week) can be part of a healthy diet for women with PCOS.