Can people with thyroid disease eat tofu?
If you have thyroid problems, you may have heard advice to avoid soy products. But is there any scientific basis for this advice? And how much soy can you eat without harming your health?
Soybeans or soybeans, soybeans are a legume that contains a lot of protein, grown as food for humans and livestock. Soybean products are used very diversely, using directly raw beans or processed products.
Soybean products are very diverse and familiar in Vietnamese people's lives such as soy milk, tofu, soy sauce, candy... meeting the protein needs in daily meals.
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, 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 that is similar to the hormone estrogen. Soybeans and soy isoflavones have been extensively studied and found to have many health benefits.
Soy may help reduce hot flashes and night sweats during menopause, reduce LDL cholesterol levels, lower 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 thought that eating soy could interfere with thyroid function, possibly causing hypothyroidism.
Laboratory and animal studies show that soy isoflavones affect thyroid hormones such as blocking thyroid hormone activity, causing hypothyroidism, reducing thyroid drug absorption from the intestine, stimulating thyroid growth causing goiter, and triggering autoimmune thyroid disease.
However, human studies 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 this did not appear to be clinically significant.
Additionally, a 2022 review of 417 studies found that soy isoflavones had no negative effects on thyroid function, thyroid hormone levels, or reproductive hormones. In other words, current research does not support labeling soy as an endocrine disruptor.
Soybeans may affect iodine
However, soy may alter thyroid function in people who are iodine deficient. Thyroid hormones are produced in the thyroid gland. Iodine, an essential dietary mineral, is a component of thyroid hormones.
Soy is thought to inhibit thyroid hormone production by blocking 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 stimulates the production of thyroid hormones. When thyroid hormones are low, TSH levels continue to rise to too high a level. This can overstimulate the thyroid gland and cause it to enlarge, forming a goiter.
Tofu is a familiar dish in the lives of Vietnamese people. Photo: NP
Too much soy can be a problem
Excessive soy consumption may alter thyroid hormone activity, but the mechanism by which these changes occur remains unclear.
For example, a 2016 study published in the Journal of Public 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.
A 2018 clinical trial suggests that this effect may be due to the isoflavones, not the soy itself. In the study, participants were given either soy protein plus isoflavones or just soy protein. After three months of daily supplementation, only the isoflavone group had increased levels of the thyroid hormones T3 and TSH.
Current research also suggests that women are more susceptible to thyroid problems associated with soy products than men. However, the reason for this different response between men and women remains unclear.
Soybeans and thyroid medication
Soy may interfere with the optimal absorption of thyroid replacement medications such as levothyroxine. This may cause your medication to produce inconsistent results.
In general, thyroid medications should be taken on an empty stomach to avoid uneven absorption. Foods and beverages containing soy should be avoided for 4 hours before and after taking the medication.
Additionally, people undergoing radioactive iodine (RAI) therapy should avoid soy products during treatment. According to the American Thyroid Association, high soy consumption can interfere with RAI therapy and should be avoided.
How much soy is healthy?
The US Food and Drug Administration (FDA) recommends that adults consume 25 grams of soy protein per day 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. Research suggests that taking 50–100 mg of soy isoflavones per day is safe, but higher amounts have not been evaluated.
So, according to current research, eating soy in moderation does not affect thyroid health. However, consuming too much soy can alter thyroid hormone levels and interfere with thyroid hormone production.
Soy isoflavones, bioactive compounds with phytoestrogenic 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 susceptible.
Physician Phung Tuan Giang, President of the Vietnam Institute for Research and Development of Traditional Medicine, added that people with a history of hormone-sensitive cancers, such as breast cancer, may choose to avoid soy products due to the soy isoflavone content, which can mimic the effects of estrogen in the body.
However, a growing number of new studies are finding that eating soy foods is not linked to a higher risk of breast cancer.
In fact, a study published in the journal Nutrition and Cancer even found that regular tofu consumption was associated with a reduced risk of developing breast cancer in premenopausal women.
Additionally, soybeans contain goitrogens, which are compounds that can interfere with thyroid hormone production.
Dr. Giang also noted that it is important to keep soy intake in moderation and enjoy it as part of a balanced diet, especially if we have a history of thyroid problems.
Sharing the same view, according to Dr. Nguyen Viet Cuong, Department of Examination, Hanoi Oncology Hospital, some studies have shown that in people with normal thyroid function and no iodine deficiency, isoflavones do not affect thyroid function. Documents also suggest that soy foods also increase the necessary hormone dose in patients with hypothyroidism.
Therefore, a diet containing a normal amount of beans is considered safe. People with hypothyroidism do not need to abstain from beans, the important thing is to ensure that the body is not deficient in iodine./.