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Soy and thyroid

Can soy cause hypothyroidism? Some foods contain compounds called goitrogens that interfere with thyroid function. In extreme cases these goitrogens can cause goiter (an enlarged thyroid gland). Increasing iodine intake prevents this goitrogenic effect of soy. Some research also indicates that heating soy eliminates part of this goitrogenic effects. Around 1950 there were several cases of goiter in infants fed with soy flour based formulas, which were not fortified with iodine. These formulas do no longer exist and infant formulas are now based on soy protein isolates (not soy flour) and are also fortified with iodine. No cases of goiter have been reported in babies fed with these formulas.

Recent studies indicate that there is little risk to thyroid function in healthy people who consume soy. However, people who have too low intake of iodine could be at risk. Increasing iodine intake is easy: this can be done by using of iodized salt or by taking iodine supplements. According to the American Thyroid Association "soy does not cause hypothyroidism, but it does interfere with the body's ability to absorb thyroid replacement therapy".
In practice, this means that thyroid medication and soy products must not be taken at the same time. The FDA rejected earlier claims that soy adversely affected the thyroid due to lack of evidence. In Asian countries where consumption of soy is 10 to 100 times higher than in the Western world there's no higher occurrence of hypothyroidism.

What if I have hypothyroisism?

Some doctors suggest that thyroid medications be taken at a different time of the day than soy protein to maximize absorption of the medication. Hypothyroidism is very common among women so you may want to have your thyroid levels checked every couple years or so, whether or not you eat soy. Hypothyroidism has not been a concern in human studies. Studies with athletes have not shown any negative effects of soy to thyroid health. The FDA has neither issued a consumer warning, nor stopped infant formula from being used, nor stopped soy foods from being sold. The FDA reviewed the medical literature for two years and found no proven evidence that soy would harm the thyroid. A lot of soy concerns come from one in vitro study, which uses pure isoflavones in high concentrations.



it affected my thyroid gland and now I have hypothyroidism, I now drink almond milk.
Daniel - 04/02/2011


There is a recent literature review published in Thyroid (2006 March) entitled "Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature."

"Soy foods are a traditional staple of Asian diets but because of their purported health benefits they have become popular in recent years among non-Asians, especially postmenopausal women. There are many bioactive soybean components that may contribute to the hypothesized health benefits of soy but most attention has focused on the isoflavones, which have both hormonal and nonhormonal properties. However, despite the possible benefits concerns have been expressed that soy may be contraindicated for some subsets of the population. One concern is that soy may adversely affect thyroid function and interfere with the absorption of synthetic thyroid hormone. Thus, the purpose of this review is to evaluate the relevant literature and provide the clinician guidance for advising their patients about the effects of soy on thyroid function. In total, 14 trials (thyroid function was not the primary health outcome in any trial) were identified in which the effects of soy foods or isoflavones on at least one measure of thyroid function was assessed in presumably healthy subjects; eight involved women only, four involved men, and two both men and women. With only one exception, either no effects or only very modest changes were noted in these trials. Thus, collectively the findings provide little evidence that in euthyroid, iodine-replete individuals, soy foods, or isoflavones adversely affect thyroid function. In contrast, some evidence suggests that soy foods, by inhibiting absorption, may increase the dose of thyroid hormone required by hypothyroid patients. However, hypothyroid adults need not avoid soy foods. In addition, there remains a theoretical concern based on in vitro and animal data that in individuals with compromised thyroid function and/or whose iodine intake is marginal soy foods may increase risk of developing clinical hypothyroidism. Therefore, it is important for soy food consumers to make sure their intake of iodine is adequate."
Rob - 04/03/2011

My soy experience

I received that email and ignored it as spam. Now I have been diagnosed as having hypothyroidism as a result of my soy milk intake. ( I changed from dairy 6 years ago, as I was lactose intolerant). Now I just don't take any form of milk, as the cow's milk did not have any far-reaching effects like the soy milk. I will now have to take hormones probably for the rest of my life to correct the damage done y soy milk.
Jacqroch - 12/04/2011

soy milk

I tried soy milk milk 3 weeks ago to see how it effected me. I have Hypothroidism and used to eat tofu a lot years ago but never used soy milk. After only two glasses of the stuff i got pain in my throat and extreme fatigue. of course i stopped using it after that. i'm not saying everyone should throw out their soy products but be careful and listen to signs your body gives you that there might be a problem. I think well-cooked tofu maybe reasonably safe but i'm not taking any chances because I've been dealing with health problems for years now because of my throid.. My advice would be to keep soy consumption low.
Rich - 10/08/2012


hi is it safe 2 eat soya with under active thyroid..thank yoy

geraldine hartford - 17/04/2014

Unfermented soy products such as milk, tofu etc seem to have potent anti nutrients and seem to add to the cause of many diseases and malnutrition, whereas fermenting releases the nutrients which are quite beneficial for health
Daniel Fink - 19/04/2014

phytate and soy

Hi, last week I went to buy soy complement for my father but the person in the store told me that I should buy fermented soy, and that taking soy daily as a complement may be bad for health, he told me that it may cause problem with the tiroid, and that you can get blind and some other problems. So he told me to look for information about phitate. So could you help me if he should keep takind his soy caps daily he has very good results taking it with his cholesterol levels, but i would like to know if there are problems if he takes it. Thanks, i will be waiting for your reply.
Suaddad - 04/09/2015

phytate and soy

Many rumors about soy are circulating on the internet. That eating soy cause blindness is a new one for me. A study published in the March 2006 issue of Thyroid shows that there is no evidence that soy foods or isoflavones affect the thyroid function in healthy adults. Another study even shows that the intake of isoflavones reduces the risk of thyroid cancer.

Phytic acid is well known for its anti-nutritional properties. But recent studies show that phytic acid has many health promoting properties: it is an antioxidant with anticancer and anti-inflammatory properties. Some scientists even want to give phytic acid the status of a vitamin.

Why not eat plain soy products such as soy milk, tofu, miso or tempeh, instead of soy supplements? Miso and tempeh are fermented soy products. They are easier to digest and have a unique taste.
Rob - 04/09/2015

Fermented soy products are a safe

Unfermented soy products are not a good idea for those who are hypothyroid or have it in their family history. Fermented soy products are a safe and valuable addition to any food program.
cccquilter - 17/12/2016

Soya and thyroid

You should not take anything with you thyroid medication, just water. Taken on an empty stomach with nothing to eat/drink for 30 to 60 minutes. Not just soy...although in my recent research(as I have been vegan for about 6 months due to severe Rheumatoid arthritis flare up) and soy just wrecks my stomach, I have discovered that soy is not as wonderful as I had been told. Fermented soy products seem to have the best health benefits. Some of what I have read is thatunfermented soy inhibits calcium absorption, can actually contribute to breast health issues, and can have an impact on many other health issues including alzheimer's, and menapause.
Jennak62 - 17/12/2016

Thyroid medication

I recently take synthroid and I am interested in taking herbalife protein shake wich has soy fiber will it interact with my medicine.
bandabelen - 25/08/2018

Thyroid medication

Studies on soy and thyroid health indicate that soy does not adversely affect thyroid hormone levels or the thyroid gland in healthy individuals consuming sufficient iodine. According to the Synthroid Prescribing Information, soybean flour and fibre in general reduces the absorption of the active components. Physicians often recommend taking thyroid medication a few hours after soy consumption, although the effect may be minimal.
Rob - 25/08/2018

Thyroid medication

Very wise...I was one of those OTC low birth moms Twice. I cannot answer about how bc would/could effect thyroid meds as I didnt start my thyroid meds until recently and Ive been post-medical-menopausal for 6 years now.
Coovetlegessy - 03/12/2019

Too much soy?

I read that consuming soy in excess is harmful to the body via the thyroid gland, and that soyprotein is not a complete protein therefore difficult to adsorb. Are these statements true or not? Thanks for your answer!
James - 07/08/2020

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