soy products

When people turn away from meat and cow’s milk, often they replace these foods with soy products. Indeed, soy is central to the diets of many North American vegetarians. But do soy foods carry unanticipated side effects?

What Is the Impact of Soy Products on Thyroid?

Q. I started eating lots of soy products when I was a young woman. I developed low-level hypothyroidism around age 40.

My nurse practitioner put me on levothyroxine and I have been taking that. I still consume soy products just about every day even though I’ve read that it is bad for my thyroid.

Dairy products give me sinus problems, so I only use butter and a small amount of cheese. I drink soy milk every day. I’ve tried to cut back on soy but I have eaten it for so long that it is hard to change!

My TSH levels are tested every year and are normal. Do I really need to worry about soy and thyroid?

How Do Soy Foods Affect Thyroid?

A. You might need to find some ways to consume fewer soy products, but since your TSH is normal and you feel good, it is not an immediate problem. Soy foods might reduce the absorption of your thyroid pill, but presumably the dose can be adjusted (Messina & Redmond, Thyroid, March 2006).

You will want to make sure you are getting adequate iodine; you can do this simply by using iodized salt in your cooking and at the table.

The idea that soy products might interfere with levothyroxine absorption is not the only concern. Some research suggests that eating a diet containing nitrate, thiocyanate or soy isoflavones might trigger an autoimmune reaction to the thyroid hormone T3 (Colucci et al, Archives of Environmental Contamination and Toxicology, Aug. 2015).

Cruciferous vegetables such as broccoli, Brussels sprouts, cauliflower, cabbage and turnips are sources of thiocyanate. Processed meats such as bacon or salami are rich in nitrate. Vegetables such as beets, spinach and collard greens also contain nitrates. Obviously, all these vegetables belong in a healthful diet, just as soy products do. The key is to consume traditionally prepared soy foods in moderation (Zaheer & Humayoun Akhtar, Critical Reviews in Food Science and Nutrition, Apr. 13, 2017).

Learn More:

You may want to listen to our interview with thyroid patient advocate par excellence Mary Shomon and thyroid expert Antonio Bianco, MD. It was Show 1015: Thyroid Mysteries, Controversies and the Latest Research. There is also more information in our Guide to Thyroid Hormones.

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  1. lou

    There is no doubt in my mind that soy affects thyroid med absorption. I was forced to go on IV nutrition due to drastic weight loss, and one of the ingredients is derived from soy. My hair started falling out, my hands and feet got cold, and I could fall asleep standing up. These are all signs that the thyroid med dose that has worked for a long time for hypothyroidism is not working now. The dose has been increased but still having hair loss. Hard to tell what the right dose is now. And this on top of hashimotos. I am getting enough iodine, or at least what was enough in the past.

  2. Pamela

    I thought soy milk was supposed to be healthy for you as well. I also have a low thyroid condition. I had checked to make sure there wasn’t any food interactions with the Synthroid I was prescribed. The search was negative at the time. I drank 1 cup of soy milk per day over a month. I gained 25 lb and my TSH reading rocketed up to 4 times the max normal. I’ve never been able to take that weight gain off even with increasing dosages of Synthroid. I have had several surgeries over the last 3 years and have either gained more weight or been unable to lose any. I discovered that I was given Propofol which is loaded with soybean oil.
    It was discovered recently, that I have now converted to autoimmune thyroiditis and soy only makes this worse. My body temp drops as does my heart rate, along with fatigue. Docs don’t seem to care, as long as it doesn’t cause an allergic reaction.

  3. Happy Oatmeal

    I have added gin soaked raisins to my morning oatmeal for over two years. It stopped my knee joint pain when I went on walks. Great old time remedy. I have told friends and they also have reduced their joint pain. I use oatmeal to dilute the alcohol to avoid heartburn. I use to take the raisins at night before bed but I would get a burning sensation in my stomach.

  4. Ann

    I have a family member with a soy and dairy sensitivity and we have learned to avoid them altogether. We drink almond milk, for example. Unless the soy product is organic it is probably tainted with cancer causing pesticides.

  5. Sandra

    Almond milk could be used instead of soy

  6. Luke

    Soy is so concentrated in protein if you find soy flour bread, one single slice is the equivalent of a few ounces of meat. Cut soy products in small pieces due to high protein content. The good news it is full amino acid (same as meat protein) but no fat and no cholesterol.

  7. Luke

    I doubt soy will adversely affect your thyroid since animal feed is primarily soy and a major dietary staple in many parts of the world. However, soy is HIGHLY concentrated protein and too much of it is no good.

  8. Lynne

    I was always told that grapefruit was a no no when taking meds for heart, thyroid, blood pressure, & diabetes. I don’t take the meds that you mentioned in your article on the subject. I used to love grapefruit & would gladly begin to eat it again if it’s safe.
    Thank you

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