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People managing a chronic condition like hypothyroidism want to avoid simple activities that might interfere with the best outcome. They may have heard that you have to take your thyroid medication early in the morning, an hour before coffee or breakfast. But what about other dietary considerations? Does soy interfere with thyroid hormones?
Does Soy Interfere with Thyroid Treatment?
Q. I have hypothyroidism and have read from some sources that soy products can make symptoms worse, while others report that soy is beneficial for thyroid disorders. Should I avoid soy or consume it?
A. Although the idea of soy disrupting thyroid function has been kicking around for decades, the science is surprisingly thin and quite confusing. An analysis of data from the National Health and Nutrition Examination Survey (NHANES) found that people consuming more flavonoids, including those from soy, had lower levels of thyroid hormone (PLoS One, May 21, 2024). That finding is slightly worrisome but inconclusive.
A six-month randomized trial in China found that soy and the soy isoflavone daidzein are safe, without any impact on thyroid function (Phytotherapy Research, Oct. 2021). Some studies in rats demonstrate that soy isoflavones can inhibit thyroid peroxidase in certain situations such as iodine depletion (Molecules, March 10, 2023). Most people using iodized salt in the US would not have inadequate iodine intake. Consequently, you might not want to make soy a mainstay of your daily diet, but including it occasionally is probably just fine.
Can You Take Thyroid Medicine in the Evening?
Q. I have hypothyroidism. I read that soy products can make symptoms worse. I’ve seen other reports that soy is beneficial for women with thyroid disorders.
I take my thyroid medicine first thing 30 minutes before I eat or drink anything. Then I have soy milk and fiber with my cereal.
Can I take thyroid medicine several hours after dinner (with no soy or fiber) just before bedtime? Should I avoid soy? I hope you can clear up my confusion.
A. You are not the only one who is confused. Researchers found that compounds in soy can inactivate an enzyme important for thyroid function (Environmental Health Perspectives, June 2002, Suppl. 3). Ever since then, scientists have been arguing about the practical importance of this discovery. People low in iodine seem especially susceptible, but we don’t know how common that is in the US. People consuming cow’s milk rather than soy milk may have an easier time getting adequate iodine (Public Health Nutrition, Sep. 2023).
Learn More:
Our eGuide to Thyroid Hormones covers several controversial issues, including the use of Armour desiccated thyroid, the balance between T3 and T4 hormones and a list of foods that can affect thyroid function. You might also want to listen to one of our podcasts on treating hypothyroidism, such as Show 1330: Rethinking Hypothyroidism.
It’s smart to avoid fiber when you take your pill, as that might reduce its absorption. In fact, taking it in the evening at least a few hours after you finish eating gives the best results (Clinical Endocrinology, Jan. 2007).
Linda
My thyroid gland was burned up when I was young by a doctor overdosing me. I landed in the hospital with my heart fibrillating, and the cardiologist was furious that I was on so much thyroid med. Anyway, it left me with a burned up thyroid gland and a left bundled branch block. I used soy products, especially soy cheese, for many years until I discovered it could interfere with the Synthroid that I had been taking. I switched to Armour and am taking 90mg. Since it is natural dessicated thyroid, does soy interfere with it?
I noticed that you mentioned sending a guide including Armour information to someone who asked about using soy with her meds. Since I am taking Armour would it be possible to send the guide to me also? I would appreciate it very much.
Thyroid can play havoc with our systems. I am also diabetic, but follow a very strict diet and take supplements to keep it under control. But I would very much like some information about Armour thyroid and soy, as well as any other information about Armour.
Thank you for providing this website for people with thyroid disease. There is so much to learn about it, and this website is a big help for people. So thank you again for providing this valuable information.
Alice
Sylmar, Ca
I have read that many goitrogenic foods are O.K. if cooked, except Soy. I have diagnosed Hashimoto’s and cannot have gluten anymore as it increases the antigenic attack on my thyroid. With my hypoglycemia I have also dropped off eating sweet potatoes which are goitrogenic. I recently started taking Cytomel (5 mcg) along with my Levothyroxine (75 mcg) and am finally having much more energy and have already lost 16 lbs in the last month even with minimal exercise. Lots of walking just wasn’t having any effect on my weight before this. Hope this is helpful.
Pat
I am on 30mg of armour a day and medifast. I was told that the soy in it would hinder my armour; is this true because I have thought about stopping medifast if it does and I have had breast cancer and was told the soy could cause breast cancer. Please let me know what to do because I am driving myself crazy trying to figure this out. Thank you
Kathy M.
United States
Has anyone answered this question? I would be interested in knowing the answer also!
BJC
I am 61 years old, have been on thyroid medications (synthroid,then switched to levothyroxine) since 1988. I bought some fish oil pills and now see that the last ingredient it contains is SOY. Is it okay to take the fish oil pills containing SOY while taking the levothyroxine? I take levothyroxine in the morning and take my vitamins late afternoon. Thanks for any info you can provide.
Cheri P
My husband was on thyroid meds–his doctor took him off to see if his thyroid would function on its own and he crashed. They told him he would be on meds for the rest of his life.
I went on a weight loss–healthy eating plan– lost 78 bs and he decided he wanted to go on it too. He has now gone from a 34″ waist to a 30″ waist, is off his meds and his thyroid is back working again. I actually became a certified health coach and he is the third client to have their thyroid come back working. Of course I do not make any promises but it is amazing how our bodies can heal themselves when we know what to eat–and we lose weight when our bodies are working properly.
Cheri P
Certified Health Coach
https://www.facebook.com/ItsSoVeryCheri
Spring
Hang on. “Soy” is an umbrella term for a huge variety of products. Different kinds of soy have variable effects. I strongly doubt that the studies showing the negative effects of soy were testing the effects of non-GMO, organic soy. 90% of soybean crops in the U.S. require heavy pesticide use (thanks in large part to the insidious Monsanto – but that’s another topic). Couple that with marketing that aims to convince consumers that soy = a miracle-food, and it’s no wonder that soy is linked to cancer.
Most soy products on our grocery-store shelves contain not soy in its purest form but rather “soy protein isolate” or “textured soy vegetable protein”. These are produced by processing soy at very high temperatures, resulting in cancer-causing substances. They’re found in fake-meat products, like Yves, as well as in soy-protein bars and soy-protein powders. And yes, they are produced with horrible pesticide-laden soybeans. Avoid these products, pervasive though they are.
I think it’s worth spending a bit more of one’s food budget to buy non-GMO, organic tofu, tempeh, or miso that has been properly fermented. And, as with everything, don’t consume it excessively.
VIV
SUSAN,
I have been taking Armour for 15 years now. Three friends I have, after taking Synthroid and still having the same symptoms, (tired, weight gain , etc.) I told them to TELL their Dr. to prescribe Armour. For some reason Drs. do not want to prescribe it (they say it is not always accurate), however, my three friends now feel soooo much better and thank me for letting them know about Armour. Ask your Dr. to do prescribe it and try it for 6 months. Good luck.
Sonni
I take 150mcg synthroid each morning at least and hour before breakfast. I have been on Medifast diet regimen and not losing weight as expected. What effect is the soy in this product affecting my weight loss and possibly making my medication ineffective?
Molly
According to my endocrinologist, the soy has to be present in a larger amount for it to be of any importance. He said to concern myself more with calcium in other foods, such as vitamins or dairy products, as this can bind with thyroid meds and render them ineffective. Soy lecithin is an emulsifier used in thousands of foods, and should have no effect on your thyroid medication.
KH
Does eating foods that contain soy lectithin affect the thyroid medication absorption also, or is it just the soy protein?
CJG
I have been “educating” myself and found very conflicting information about taking iodine-iodide supplements or consuming iodine while having Hashimoto’s Thyroididtis. I am currently taking Synthroid in the morning and multi-vitamins and supplements at noon having switched from Levothyroxin which stopped working. Now, the Synthroid is no longer working.
I am considering switching to the Levothyroid which, after 15 years, my 30 yr old daughter has found to be the only medication that works for her.
Who has the ultimate, unbiased word on iodine-iodide and Hashimoto’s?
Molly H.
Regarding soy and the thyroid, the word is “goitrogens” and foods containing them thought to sometimes be a problem for people who have untreated hypothyroidism and have low iodine. If you are taking thyroid medication and getting adequate iodine supplementation, you should be fine to consume soy foods. The old research is outdated and is being revised. Here is a study that was just released:
http://www.ncbi.nlm.nih.gov/pubmed/20357174
In it, researchers gave the group 54 mg genistein (the isoflavone in soy) daily for three years to postmenopausal women, which is what one would find in 2-4 cups (depending on brand) of soy milk (so, quite a lot!), and it did not affect thyroid health in any way compared to placebo.
I spoke at length with my endocrinologist, who was voted by Texas Monthly magazine as one of the “Top Docs” in Texas, and he said that goitrogens are not something that I should worry about, since I take thyroid medication and have adequate iodine supplementation.
He said they are really only of concern for people (1.) living in 3rd world countries who are not getting iodine in their diets, or (2.) people who are eating very large quantities of them and NOT taking thyroid medication correctly.
I hope this helps – it assuaged my fears a lot.
Cindy P.
I would try to avoid Soy & Soy oil as much as possible. Soy is part of a list of foods hypothroid patients should avoid called goiterns. If you start to eliminate these foods from your diets, you should start to see a change. I know I did. I would agree with Molly H. & educate yourself as much as you can.
Molly H.
If you have clinical hypothyroidism, you will have to supplement with something forever, but not necessarily with Synthroid. You have options. One option is Armour, which is available at larger pharmacies, another option is combining Synthroid with Cytomel, which is the synthetic version of T3, and may make you feel MUCH better. If you are not already seeing an endocrinologist, I urge you to find a good one.
The book “The Thyroid Solution” by Dr. Ridha Arem is an excellent resource, as is “Living Well with Hypothyroidism” by Mary Shomon. Educate yourself about your condition, and you will have much better results… I did!
Susan12
I, too, am hypothyroid. I have been taking 75 mcg daily of synthroid for 5 years. I am still tired all the time, my hair is still falling out, I have gained at least 15 lbs and have continually asked my doctor: do I have to take the synthroid forever? Her response is “yes”. My question is where can I find Armour desiccated thyroid and is it appropriate to continue taking synthroid along with taking the Armour?
Thanks
PEOPLE’S PHARMACY RESPONSE: ARMOUR THYROID IS A PRESCRIPTION DRUG. IT IS NOT USUALLY MIXED WITH SYNTHROID. MANY DOCTORS PREFER NOT TO PRESCRIBE IT BECAUSE THEY ARE NOT FAMILIAR WITH IT.
MBD
I’ve always been told to take the thyroid pill on waking, at least 1/2 hour before eating. In your response, you said “taking it in the evening”. Did you mean the pill? or the soy? If you meant the pill, will that be affected by a 5 mg. Ambien I may take later? If so, how much time should elapse between the Levoxyl and Ambien? Oy!
PEOPLE’S PHARMACY RESPONSE: AMBIEN DOES NOT SEEM TO INTERFERE WITH LEVOXYL ABSORPTION. WHETHER YOU TAKE THE LEVOXYL UPON ARISING (AT LEAST 30 MINUTES BEFORE COFFEE, TEA OR BREAKFAST) OR JUST BEFORE BED (AT LEAST 2 HOURS AFTER SUPPER AND OTHER FOOD) DEPENDS UPON YOUR SCHEDULE AND YOUR OTHER DRUGS. WE RECENTLY HEARD FROM A PERSON WHO MUST TAKE AN ANTACID AT NIGHT. FOR HIM, IT IS BETTER TO TAKE THE LEVOTHYROXINE IN THE MORNING, SINCE ANTACIDS INTERFERE WITH LEVO-T ABSORPTION.