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In recent decades, soy has become a popular food across the globe. Although soy has health benefits, it also has side effects. In some cases, soy can adversely affect your thyroid function and hormonal health. Ahead, a look at soy and whether it can be part of a healthy diet when you’re hypothyroid.

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Soy is a versatile legume widely used as a source of nutrition and in various food products and is featured in many cuisines worldwide. Soybeans are high-protein edible beans that are commonly processed to produce a variety of soy-based products, including:

Traditional Soy Products

• Edamame: boiled or steamed and seasoned soybeans
• Tofu: a soft, cheese-like food made from soy milk
• Soy Nuts: roasted soybeans that can be eaten as a snack.
• Soy Flour: a fine powder made from roasted soybeans that can be used in baking and cooking

Fermented Soy Products

• Miso: a paste made from fermented soybeans that is used as a seasoning in Japanese cuisine.
• Tempeh: a cake-like product made from fermented soybeans that can be sliced and used in sandwiches or stir-fries.
• Natto: a traditional Japanese food made from fermented soybeans that has a sticky texture and strong flavor

Soy Milk and Dairy Alternatives

• Soy Milk: a plant-based milk made from whole soybeans or soy protein isolate that can be used as a dairy milk alternative.
• Soy Yogurt: a dairy-free yogurt made from soy milk.
• Soy Cheese: a dairy-free cheese made from soy milk

Soy-Based Meat Alternatives

• Soy Burgers: a vegetarian or vegan alternative to beef burgers made from soy protein.
• Soy Sausages: a vegetarian or vegan alternative to pork sausages made from soy protein
• Soy Nuggets: a vegetarian or vegan alternative to chicken nuggets

Other Soy-Based Foods

• Soy-based Sauces: shoyu, tamari, and teriyaki sauces made from fermented soybeans, wheat, and salt.
• Soybean Oil: an oil extracted from soybeans commonly used in cooking and baking.
• Soy Nut Butter: a spread made from ground soybeans that can be used as an alternative to peanut butter

Supplements

Soy is also an ingredient in a variety of health supplements, including:

• Soy-based protein powders
• Soy-based menopause supplements
• Soy lecithin, which is often used as an emulsifier in supplements

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Soy has more protein and fat – and fewer carbohydrates – than other legumes. The quality of soy protein is also considered much higher than other plant proteins.

The carbohydrates in soybeans can act as prebiotics. Prebiotics are non-digestible compounds that promote the growth and activity of beneficial bacteria in the gut. They essentially serve as food for the good bacteria, allowing them to thrive and improve the overall health of the gastrointestinal system.

Soybeans are also a good source of vitamins and minerals, including potassium, iron, calcium, and omega-3 essential fatty acids.

Soy’s high level of protein makes it a popular food choice for vegetarians and vegans. The low carbohydrate content means that soy is also a good food option for people with diabetes or dieters cutting back on carbohydrates as part of a weight loss program.

Soybeans and soy foods also include isoflavones, the active components responsible for soy’s hormonal and non-hormonal effects. The chemical structure of isoflavones is similar to the hormone estrogen, and they’re able to bind to estrogen receptors in various organs, including the skin, spleen, pancreas, kidney, thymus, adrenal gland, brain, pituitary, ovaries, and testes. Isoflavones are found almost exclusively in the members of the bean family, and soybeans and soy foods are particularly rich sources.

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Soy is reported to have many health benefits. (Keep in mind, however, that most of the studies on soy have been conducted on animals, not humans, and many of the human studies have mixed or inconclusive results as to benefits.)

Some of the health benefits attributed to soy include the following:

• Soy is a nutrient-dense plant-based source of protein that provides a low-fat, low-carbohydrate alternative to red and processed meat
• Soy is a natural source of polyphenols, antioxidant compounds that have anti-inflammatory properties. Polyphenols can help reduce the risk of chronic diseases like heart disease, cancer, and neurodegenerative disorders. Additionally, polyphenols may also promote gut health, improve digestion, regulate blood sugar levels, and support weight management.
• Soy is rich in isoflavones, compounds that have been shown to have potential health benefits such as reducing the risk of heart disease and osteoporosis.
• Soy may help lower blood sugar levels.
• Soy may help reduce the risk of cancer. (Note: Some analyses suggest that soy consumption can reduce the risk of prostate cancer in men and that soy’s isoflavones may help reduce the risk of cancer.)
• Soy may help menopausal symptoms. (It’s important to mention that while soy products are frequently recommended for menopausal symptoms, the research findings are mixed and have not established benefits conclusively.)

There’s also a great deal of hype about soy’s benefits for heart health. Specifically, some studies claim that soy helps lower cholesterol levels and help reduce the risk of heart disease. Beginning in 1999, the U.S. Food and Drug Administration even permitted soy products to carry a label stating that soy protein reduces the risk of heart disease. However, in 2017, the FDA proposed revoking this approval based on more recent results that showed mixed findings regarding soy’s benefits for heart health.

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While soy clearly has some health benefits, there are potential risks associated with consuming soy products.

Allergies and sensitivities: While most people can safely consume soy products, a small percentage of people – estimated at less than 1% of the population – have an allergy to or intolerance of soy products. The symptoms of a soy allergy can vary from mild to severe and can include hives, itching, swelling, abdominal pain, vomiting, diarrhea, difficulty breathing, and in severe cases, anaphylaxis.

Digestive upsets: Digestive problems caused by soy can range from mild discomfort to more severe symptoms such as bloating, gas, flatulence, and diarrhea. Soy contains a compound called oligosaccharides, complex sugars the human body has difficulty digesting. These oligosaccharides can ferment in the intestines, leading to the production of gas and resulting in digestive issues.

Estrogenic effect: One of the main concerns is that soy contains phytoestrogens, plant chemicals that mimic the hormone estrogen in the body. At higher levels of consumption – or concentrated in supplements – phytoestrogens can disrupt hormonal balance and potentially lead to adverse health effects, particularly for pregnant women and individuals with certain hormone-related conditions. Elevated levels of estrogen are also associated with an increased risk of breast cancer.

Medication Interactions: Soy may interact with certain medications, including blood-thinning medications like warfarin (Coumadin), as well as medications like Tamoxifen that treat hormone-sensitive conditions such as breast cancer.

Soy can also interfere with antidepressants, an issue that has been a topic of concern and extensive study. Some research suggests that consuming soy products may interfere with the effectiveness of certain antidepressant medications, particularly those that are selective serotonin reuptake inhibitors (SSRIs). Commonly-prescribed SSRIs include fluoxetine (Prozac), sertraline (Zoloft), escitalopram (Lexapro), paroxetine (Paxil), and citalopram (Celexa). These medications work by increasing the levels of serotonin in the brain. Soy products, specifically genistein, a compound found in soy, may potentially bind to serotonin receptors and reduce the effectiveness of SSRIs.

If you are taking any medications, be sure to discuss soy consumption and potential interactions with your healthcare professional or pharmacist.

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Soy products can potentially pose additional risks for people with autoimmune Hashimoto’s thyroiditis and hypothyroidism.

Goitrogenic effect: Some people who suffer from Hashimoto’s and hypothyroidism may react adversely to compounds found in soy called “goitrogens.” Found in cruciferous vegetables and soy, goitrogens are compounds that inhibit the thyroid’s ability to utilize iodine. Specifically, goitrogens can slow thyroid function and promote thyroid enlargement (goiter.) These same compounds can even disrupt your ability to absorb other essential vitamins and minerals if consumed too frequently or in excess amounts – something to keep an eye on if you decide to give some type of dietary soy supplement a try.

Medication absorption: Soy has the ability to interfere with the absorption of your thyroid hormone replacement medication used to treat hypothyroidism. If you are taking levothyroxine or a natural desiccated thyroid drug, make sure your doctor is aware of your soy consumption, and consider separating your soy intake from taking thyroid medication by three to four hours.

Slowed thyroid function: A higher soy intake can slow your thyroid function, and the effect is most pronounced in people who are also deficient in iodine. One 2016 study found that your chance of developing an elevated thyroid stimulating hormone (TSH) level is four times higher if you eat two servings of soy foods daily compared to people who don’t eat soy.

Blocking iodine and zinc: Soy contains compounds called phytates, which can bind to minerals like iodine and zinc and prevent their absorption in the body. Iodine is an essential nutrient needed for the production of thyroid hormones. Zinc is also crucial for thyroid function and other physiological processes, including immune system support and DNA synthesis. When soy is consumed in excessive amounts or in a way that hinders digestion and absorption, it can interfere with the body’s ability to utilize these essential minerals. Therefore, it is crucial to be mindful of soy intake and ensure adequate consumption of iodine and zinc from other food sources or supplements.

Blocking TPO: The isoflavones in soy can be problematic for some people with an underactive thyroid and Hashimoto’s. They have the ability to block the function of the thyroid peroxidase (TPO), an enzyme that is necessary for the thyroid to be able to produce T3 and T4 hormones (38-40).

Endocrine disruption: Given their hormonal effect, isoflavones are considered endocrine disruptors, which can negatively affect hormonal balance at higher concentrations.

Autoimmune flares: Soy can trigger or exacerbate autoimmune flare-ups and symptoms in susceptible people. According to Paloma’s Director of Research, Dr. Vedrana Högqvist Tabor, as many as 1 in 4 people with Hashimoto’s thyroiditis report that soy is a trigger of their autoimmune flares.

Increased dose of thyroid medication: There is a growing body of research exploring the potential effects of soy consumption on thyroid function and the dosages of thyroid hormone replacement medication. Some studies suggest that individuals on thyroid hormone replacement therapy might need to adjust their dosage if they consume high amounts of soy.

Increased TSH levels: A systematic review and meta-analysis studying the effect of soy on thyroid function concluded that soy can modestly raise TSH levels.

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As you can see, there are concerns that soy may have a negative effect on thyroid function, particularly in individuals with hypothyroidism. Here’s what the research suggests about how to eat soy if you have a thyroid condition:

Go non-GMO: If you choose to incorporate soy foods in your diet, make sure that you choose soy that has not been genetically modified, also known as “non-GMO soy.” GMO stands for “genetically modified organisms.”

The main difference between GMO soy and non-GMO soy is the way they are produced. GMO soy is genetically modified to have certain traits, such as resistance to pests or herbicides. With GMO soy, the DNA of the soybean plant is altered in a laboratory. GMO soy is also frequently grown using large-scale industrial farming practices and may involve the use of toxic chemicals to control pests, which can be harmful. It’s also important to note that GMO soybeans are most commonly used as livestock feed.

Non-GMO soy is produced through traditional breeding methods without any genetic modification. It’s typically grown using organic or sustainable farming methods. The farming practices for non-GMO soybeans help maintain healthy soil and reduce the use of toxic chemicals.

Many healthcare practitioners recommend that you choose only non-GMO soy. Because it is grown naturally without any genetic changes, non-GMO soybeans retain their natural nutritional profile and are not subject to any potential health risks associated with genetic modification. Additionally, non-GMO soy is often grown using sustainable farming practices, which reduces the use of harmful pesticides and promotes soil health. Choosing non-GMO soy products supports sustainable agriculture and helps to preserve biodiversity.

Eat soy in moderation: Moderate consumption of soy foods is generally considered safe for individuals with hypothyroidism. Most of the risks of soy are associated with excessive consumption of soy or soy supplements.

Avoid processed soy foods: It’s recommended to consume minimally processed whole food forms of soy, such as organic, non-GMO tofu, tempeh, and edamame, rather than highly processed soy products like soy protein isolates, protein powders, and soy supplements. Minimally processed soy foods also contain lower levels of isoflavones, which are the compounds in soy that may affect thyroid function.

Get adequate iodine intake: Getting enough dietary or supplemental iodine is crucial when consuming soy because the goitrogens in soy can interfere with your ability to absorb and utilize iodine. When iodine levels are insufficient, the thyroid gland may enlarge in an attempt to compensate, leading to goiter and potentially triggering or worsening hypothyroidism. Good sources of iodine include seafood, dairy products, and iodized salt. (You can learn more about iodine in Paloma’s free Iodine Thyroid Guide.)

Separate soy from your thyroid medication: If you are taking thyroid medication, it is important to avoid taking it at the same time as you eat soy foods. Soy can interfere with the absorption of thyroid medication, making it less effective. It would be best to wait at least three to four hours after taking your thyroid medication before consuming any soy products. By waiting, you allow enough time for your body to absorb the medication thoroughly before the potential interaction with soy. By spacing out the timing between your medication and soy consumption, you can ensure that you are getting the maximum benefit from your thyroid medication.

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For more guidance on how to follow a thyroid-friendly diet when you’re hypothyroid, consider having a virtual consult with one of Paloma’s knowledgeable nutritionists, who can help ensure that your diet complements the optimal treatment of your underactive thyroid.

Remember: if you regularly eat soy products and are hypothyroid, you’ll want to have your thyroid levels checked regularly. Typically, a thyroid panel is done before you make dietary changes that can affect your thyroid treatment and periodically after that to assess your thyroid health and function over time. You may find this testing process more accessible by using a convenient home test kit from Paloma Health, which evaluates thyroid stimulating hormone (TSH), Free Thyroxine (Free T4), Free Triiodothyronine (Free T3), and Thyroid Peroxidase Antibodies (TPOAb).

You may also want to consult with a knowledgeable healthcare provider before consuming soy or making significant changes to your diet. Paloma’s team of expert practitioners can provide personalized advice and guidance to help ensure that you have optimal thyroid treatment. They’ll work with you to map out a personalized plan for optimal wellness and thyroid health. Get started by scheduling an appointment with a Paloma provider today.

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