By Angela Grassi, MS, RDN, LDN 

 Medically reviewed by Peter Weiss, MD

Many women with polycystic ovary syndrome (PCOS) are confused about whether or not soy is good for them. Some women even fear it.

This confusion, however, stems from inaccurate nutrition information on the internet about the health benefits or actions of soy. In fact, the research that is available has indicated that regular intake of small amounts of soy can actually improve female fertility and metabolic aspects of PCOS.

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What Is Soy?

Unprocessed fermentable soy has been used as a diet staple by Asian countries for thousands of years. Soy is a plant food which contains all the essential amino acids, making it a complete protein source. Soy is low in fat, contains essential fatty acids, and is packed with vitamins, minerals, flavonoids, and fiber.

Soy is a phytoestrogen, meaning it can very weakly mimic estrogen and does not compare to the full strength of estrogen. Lab tests show that phytoestrogens in soy are approximately 100 to 1000-fold lower than that of estrogen. Soy, especially in small amounts (a few servings a week) has not been found to cause thyroid disorders. Soy is not harmful or evil for that matter, for women with PCOS.1

Health Benefits of Soy

Soy has been shown to provide many health benefits. These include relief of menopausal symptoms like hot flashes, prevention of breast and prostate cancer, reduction in bone turnover and reducing the risk for osteoporosis, and prevention of heart disease.1

In 1998, the FDA issued a food claim 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." 

Food Sources of Soy

Since the FDA ruling, there has been a large increase in the number of soy products sold in the U.S. Many of these foods are from processed soy, and not the tradition unprocessed, fermented soy typically used in Asian cultures such as tempeh or miso.

Health benefits of soy are believed to come from unprocessed soy. Processed types of soy have been associated with negative health implications such as affecting thyroid function.1 

Soy protein isolate along with hydrogenated soybean oil, for example, is often added to energy and granola bars and meat-alternative products. These forms of soy are processed. Checking the ingredient list on food labels will help you to know what form of soy if any, are in your foods. Here are some examples of processed and unprocessed sources of soy:

Unprocessed Food Sources of Soy

• Tofu

• Natto

• Tempeh

• Miso

• Soy sauce

• Edamame

• Soy nuts

Processed Food Sources of Soy

• Soy milk and cheese

• Textured soy protein (TSP)

• Soy-based protein powders

• Hydrogenated soybean oil

• Meat alternative products

• Soy protein isolate

Health Benefits of Soy for PCOS

While the research about soy intake for women with PCOS is limited, the results are showing soy can improve many metabolic aspects of PCOS. These include reducing total and LDL (the “bad” cholesterol), triglycerides, inflammatory markers, blood pressure, and insulin. Soy intake has also been shown to reduce testosterone and be protective against oxidative stress.

A study published in 2016 in the Journal of Clinical Endocrinology and Metabolism randomized 70 women with PCOS into two groups to take either 50 mg/d soy isoflavones or a placebo for 12 weeks. Metabolic, endocrine, inflammation, and oxidative stress markers were established at the beginning of the study and at the end of the trial. 

Compared to the placebo group, those who received soy significantly decreased their levels of insulin. Supplementation with soy resulted in significant reductions in free androgen index and triglycerides compared to the placebo group.2

Other studies investigating the use of soy in women with PCOS found that soy improved total and LDL cholesterol.

Soy and Fertility

While there aren’t any studies that look at how soy may impact fertility in women with PCOS, there are studies that have looked at soy use in infertile women.

A study published in 2015 in Fertility and Sterility looked at the relation of soy phytoestrogen intake in 315 women undergoing infertility treatment with assisted reproductive technology (ART) at Massachusetts General Hospital.

This study found that soy not only improved the fertilization rate, but the rates of pregnancy (52% vs. 41%) and live births (44% vs. 31%) were higher in women who ate soy compared with those who did not eat soy. Women with the highest amount of soy intake had significantly higher odds of live births than those with the lowest intake.3

Tips for Incorporating Soy into Your Diet

• Choose unprocessed, non-GMO soy foods.

• Avoid eating a large amount of meat alternative foods.

• Avoid foods that contain soy protein isolate or hydrogenated soybean oil.

• Use firm tofu or tempeh in place of meat in stir-fries.

• Make smoothies using soy milk and silken tofu.

• Enjoy edamame as a snack or toss into salads or noodle dishes.

• Add grilled tofu to a salad.

• Enjoy soy nuts as a snack.

• Use soy nut butter in place of peanut butter.

• Add miso or soy sauce to flavor dishes. 

• Add tofu or tempeh into a sandwich or wrap. 

Sources

Messina M. Soy and health update: evaluation of the clinical and epidemiologic literature. Nutrients. 2016;8(12):754. doi:10.3390/nu8120754

Jamilian M, Asemi Z. The effects of soy isoflavones on metabolic status of patients with polycystic ovary syndrome. The Journal of Clinical Endocrinology & Metabolism. 2016;101(9):3386-3394. doi:10.1210/jc.2016-1762

Vanegas JC, Afeiche MC, Gaskins AJ, et al. Soy food intake and treatment outcomes of women undergoing assisted reproductive technology. Fertility and Sterility. 2015;103(3):749-755.e2. doi:10.1016/j.fertnstert.2014.12.104

Additional Reading

Chavarro JE, Mínguez-Alarcón L, Chiu YH, et al. Soy intake modifies the relation between urinary bisphenol a concentrations and pregnancy outcomes among women undergoing assisted reproduction. The Journal of Clinical Endocrinology & Metabolism. 2016;101(3):1082-1090. doi:10.1210/jc.2015-3473

By Angela Grassi, MS, RDN, LDN
 Angela Grassi, MS, RDN, LDN, is the founder of the PCOS Nutrition Center.