Soy and PCOS: Safe or Harmful?
Are you confused about soy and are wondering if it’s safe for women with PCOS to eat? You’re not alone. One of the most confusing topics regarding nutrition and PCOS is soy. Here is what the latest research shows about soy for women with PCOS, infertility, and those with thyroid disorders and what we have to say about it.
What Is Soy?
Soy is a plant food that is also a complete protein, meaning it has all the required amino acids. It is also low in fat, contains essential fatty acids, numerous vitamins, minerals, and fiber. Unprocessed fermentable soy has been used as a diet staple by Asian cultures for thousands of years. Rates of processed soy have increased in the U.S. over the past decade.
Soy is a phytoestrogen. This means it can very weakly mimic the actions of estrogen. Lab assays show that phytoestrogens in soy are approximately 100 to 1000-fold lower than that of estrogen.
Soy isoflavones are compounds found in soy called flavonoids. Each gram of traditional soy protein provides 3 to 4 grams of isoflavones.
Proven Health Benefits of Soy
- Soy has been shown to provide many health benefits. These include:
- Relief of menopausal symptoms
- Prevention of breast and prostrate cancer
- Reduction in bone turnover
- Prevention of heart disease
Unprocessed Food Sources of Soy
- Soy sauce
- Soy nuts
Processed Food Sources of Soy
- Soy milk and cheese
- Textured soy protein (TSP)
- Soy-based protein powders
- Hydrogenated soy bean oil
- Meat alternative products
- Soy protein isolate
Soy protein isolate along with hydrogenated soybean oil, are often added to energy and granola bars and meat-alternative products. These forms of soy are processed and not the traditional forms of soy. There is evidence of processed soy foods like soy protein isolate being harmful to health in high amounts.
Soy and PCOS
While research is limited (there is only 5 published studies), investigating soy use in women with PCOS, the research is overwhelming favorable for its use in improving metabolic aspects. None of the studies showed any ill-effects of soy use among women with PCOS.
Benefits of Soy for Women with PCOS:
- Reduction in Total and LDL cholesterol
- Reduction in Insulin
- Reduction in inflammatory markers
- Reduced oxidative stress
- Reduction in testosterone
A randomized, double-blind, placebo-controlled study (the best study design around), published in Journal of Clinical Endocrinology and Metabolism, showed that soy intake significantly improved insulin resistance, triglycerides, LDL and cholesterol. The study even showed soy can increase the antioxidant glutothine, thereby reducing oxidative stress.
Several previous studies also have demonstrated the cholesterol lowering benefits of soy in women with PCOS.
Romualdi et al showed that women with PCOS who took soy (36 mg/day of isoflavones) for 6 months showed decreases in LDL and total cholesterol. Thyroid function was not affected by this dose.
Khani et al also found that women with PCOS who took 36 mg/day of soy isoflavones for 3 months saw reductions in LDL as well as triglycerides, LH, testosterone and DHEAS.
Soy and Fertility
So, what about soy’s impact on female fertility? After all, soy is a phytoestrogen, right? (Again, soy does not come close to the strength of estrogen). Those who believe soy negatively affects female fertility may be surprised to learn that the research shows the opposite: soy intake has been positively associated with improving live births, pregnancy rates, and fertilization rates.
There are 2 randomized trials of soy use among 147 women undergoing treatment for infertility.
Shahain and colleagues randomized 147 women with infertility to clomid and a phytoestrogen supplement (120mg/day) or clomid alone. The pregnancy rate was significantly higher (36%) in women who took phytoestrogens compared to those who didn’t (14.6%).
In their randomized trial, Unfer and colleagues gave 213 women undergoing IVF a isoflavone supplement (1,500mg/day) or placebo. Pregnancy and delivery rates among the women receiving soy isoflavones was nearly double that of placebo (30.3% vs. 15.2%).
A prospective cohort study 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 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. The average total isoflavone intake among soy users in this study was 3.4mg/day, much lower amounts than reported in other studies. Women with the highest amount of soy intake had significantly higher odds of live births than those with the lowest intake.
The mechanism to describe soy’s positive influence on fertility is not yet clear. Both randomized studies did show that phytoestrogen supplements increased endometrial thickness.
Soy may protect against the endocrine disruptor BPA.
BPA levels have been found to be higher in women with PCOS. High levels of BPA may affect fertility. A study published in the Journal of Clinical Endocrinology and Metabolism showed that women who did not eat soy, had higher levels of BPA and lower pregnancy and birth rates. In women who consumed soy as part of their regular diet, BPA concentrations had no impact on IVF outcomes.
Soy and Hypothyroid
Well, what about soy causing thyroid disorders? Women with PCOS have been found to have a higher incidence of thyroid disorders. This is where the research is mixed. Several randomized controlled trials show that soy can cause thyroid disorders while other randomized trials show the opposite. Very limited research indicates a link between soy affecting thyroid medications. Much more research needs to be done in these areas. So far, the majority of research available shows that small amounts of soy does not impact thyroid function in those with or without thyroid disorders.
A randomized, double-blind controlled trial examined the effects of soy in individuals with subclinical hypothyroidism.
In this study by Sathyapalan and colleagues, individuals (mostly women) were given two different levels of soy intake: 16 grams per day typically seen in vegetarians and 2 grams per day, an average soy intake in the Western diet for 16 weeks (8 weeks per diet).
Six patients (10%) developed overt hypothyroidism after eating the high soy protein diet. None of the patients developed hypoythroidism from the low soy intake diet. Of the 63% of the individuals with positive TPO antibodies, only one developed overt hypothyroidism eating the high soy diet.
Significant reductions in blood pressure, insulin resistance, and inflammatory markers (hs-CRP) were shown with the higher dose of soy supplementation.
The researchers suggest that a high soy diet (16 mg/day or more) may precipitate overt hypothyroidism for female patients with subclinical hypothyroidism and that soy intake should be monitored with caution in this population.
A review of 14 trials that involved soy intake and thyroid function in healthy adults and those with hypothyroid was published in Thyroid. With only one exception, either no effects or very modest changes in thyroid function with soy intake was found.
The researchers concluded that hypothyroid patients do not need to avoid soy.
Women with PCOS have enough things to worry about. Soy doesn’t need to be one of them.
Consuming moderate amounts (a few servings a week) of traditionally prepared, unprocessed soy in non-GMO form may offer health benefits to women with PCOS who do not have thyroid disorders. These benefits include reductions in LDL cholesterol and triglycerides and possible reductions in insulin resistance. Soy may also provide protection against oxidative damage in women with PCOS.
Women with PCOS who are trying to conceive may find that moderate intakes of soy could improve their fertility.
Those with thyroid disorders may want to be cautious with their intake of soy, avoiding high amounts, but do not need to fear it. Having a diet with sufficient amounts of iodine and regular monitoring of thyroid tests is recommended.
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