Is it okay to eat tofu if you have a thyroid condition?
If you have thyroid problems, you may have heard advice to avoid certain products. But is this advice actually scientifically sound? And how much soy can you eat without harming your health?
Soybeans are a type of legume rich in protein, grown as food for humans and livestock. Products derived from soybeans are used in a wide variety of ways, either as raw beans or in processed forms.
Soy-based products are diverse and familiar in Vietnamese life, such as soy milk, tofu, soy sauce, and confectionery, meeting the protein needs in their daily diet.
Soy protein and isoflavones
According toVerywell HealthSoybeans have been a staple food in Asia for centuries and have been part of the Western diet since the 1950s. Soybeans are a healthy and complete source of protein, and are rich in vitamins, minerals, fiber, and heart-healthy polyunsaturated fats.
Soybeans are a healthy and complete source of protein, packed with vitamins, minerals, fiber, and heart-healthy fats. Photo: Shuterstock
Soybeans also contain bioactive compounds called isoflavones, a type of phytoestrogen similar to the hormone estrogen. Soybeans and soy isoflavones have been extensively studied and found to possess numerous beneficial health properties.
Soybeans may help reduce hot flashes and night sweats during menopause, lower LDL cholesterol levels, reduce blood pressure in people with hypertension, preserve bone health after menopause, and reduce the risk of breast cancer.
Soybeans and thyroid function
For many years, it was believed that eating soy could interfere with thyroid function, potentially causing hypothyroidism.
Laboratory and animal studies have shown that soy isoflavones affect thyroid hormones by inhibiting thyroid hormone activity, causing hypothyroidism, reducing the absorption of thyroid medication from the intestines, stimulating thyroid growth leading to goiter, and activating autoimmune thyroid disease.
However, studies in humans have not shown similar results. A 2019 meta- analysis of 18 clinical trials found that soy had no effect on overall thyroid function. Soy supplementation was associated with a slight increase in thyroid-stimulating hormone (TSH) levels, but it did not appear to be clinically significant.
Furthermore, a 2022 review of 417 studies found that soy isoflavones had no negative impact on thyroid function, thyroid hormone levels, or reproductive hormones. In other words, current research does not support considering soy as an endocrine disruptor.
Soybeans can affect iodine levels.
However, soy may alter thyroid function in people with iodine deficiency. Thyroid hormones are produced in the thyroid gland. Iodine, an essential mineral in the diet, is a component of thyroid hormones.
Soybeans are thought to inhibit thyroid hormone production by interfering with the entry of iodine into the thyroid gland. This may trigger a feedback mechanism that stimulates the pituitary gland to secrete more TSH.
TSH normally functions to promote the production of thyroid hormones. When thyroid hormone levels are low, TSH levels continue to rise to excessively high levels. This can overstimulate the thyroid gland and cause it to enlarge, forming a goiter.
Tofu is a familiar dish in the daily lives of Vietnamese people. Photo: NP
Too much soy can be a problem.
Consuming too much soy may alter thyroid hormone activity, but the mechanisms by which these changes occur are not yet fully understood.
For example, a 2016 study published in the Journal of Community Health Nutrition concluded that the likelihood of having high TSH was four times higher in people who ate two servings of soy foods daily compared to those who ate none at all.
A 2018 clinical trial suggested this effect might be due to isoflavones rather than soy. In this study, participants were given either soy protein plus isoflavones or soy protein alone. After three months of daily supplementation, only the isoflavone group showed elevated levels of thyroid hormones T3 and TSH.
Current research also suggests that women are more susceptible to thyroid problems related to soy products than men. However, the reason for this difference in response between men and women remains unclear.
Soybeans and medications for thyroid disease
Soybeans may interfere with the optimal absorption of thyroid replacement medications such as levothyroxine. This could cause your medication to produce inconsistent results.
Generally, thyroid medication should be taken on an empty stomach to avoid uneven absorption. Foods and drinks containing soy should be avoided for 4 hours before and after taking the medication.
Additionally, people undergoing radioactive iodine (RAI) treatment should avoid soy products during treatment. According to the American Thyroid Association, consuming large amounts of soy can interfere with radioactive iodine therapy and should be avoided.
How much soy is good for your health?
The U.S. Food and Drug Administration (FDA) recommends that adults consume 25 grams of soy protein daily as part of a heart-healthy diet.
Soy is also sold as a dietary supplement in capsule and powder form as soy protein or soy isoflavones. Studies suggest that taking 50-100mg of soy isoflavones daily is safe, but higher amounts have not been evaluated.
Thus, according to current research, moderate consumption of soy does not affect thyroid health. However, excessive consumption of soy may alter thyroid hormone levels and interfere with thyroid hormone production.
Soy isoflavones, bioactive compounds with phytoestrogen properties, have beneficial effects on cardiovascular health and may reduce menopausal symptoms. However, high doses of soy isoflavones have been shown to increase TSH and T3 levels. Women are particularly more susceptible to these effects.
According to Traditional Medicine Practitioner Phung Tuan Giang, Chairman of the Vietnam Institute for Research and Development of Traditional Medicine, people with a history of hormone-sensitive cancers, such as breast cancer, may choose to avoid soy products due to their high content of soy isoflavones, which can mimic the effects of estrogen in the body.
However, a growing number of new studies are finding that eating soy-based foods is not associated with a higher risk of breast cancer.
In fact, a study published in the journal Nutrition and Cancer even found that regularly eating tofu was associated with a reduced risk of developing breast cancer in premenopausal women.
Additionally, soybeans contain goitrogens, which are compounds that can interfere with the production of thyroid hormones.
Dr. Giang also noted that it is important to maintain moderate soy intake and enjoy it as part of a balanced diet, especially if one has a history of thyroid problems.
Sharing the same view, according to Dr. Nguyen Viet Cuong, Department of Examination, Hanoi Oncology Hospital, some studies indicate that in people with normal thyroid function and no iodine deficiency, isoflavones do not affect thyroid function. The literature also suggests that soy-based foods may increase the necessary hormone levels in patients with hypothyroidism.
Therefore, a diet containing a normal amount of beans is considered safe. Patients with hypothyroidism do not need to avoid beans; the important thing is to ensure their bodies do not suffer from iodine deficiency.