Can soy suppress thyroid function?

I’ve heard that soy can suppress the thyroid. Is there an upper limit?

Eric Needs / Originally posted on Soy Hormones & Male Infertility


Excellent question! Soy does indeed have so-called “goitrogenic” compounds (as do broccoli-family vegetables and flax seeds), which can interfere with thyroid function in people with marginal iodine intake. The answer is not to avoid these super healthy foods but to just make sure you get enough iodine. See my videos Avoiding Iodine Deficiency and Pregnant Vegans at Risk for Iodine Deficiency.

For another reason, though, restricting one’s soy intake to 3-5 servings a day is probably a good idea. See How Much Soy Is Too Much? and Too Much Soy May Neutralize Benefits.

Image Credit: sleepyneko / Flickr

Dr. Michael Greger

About Michael Greger M.D.

Michael Greger, M.D., is a physician, author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial. Currently Dr. Greger proudly serves as the Director of Public Health and Animal Agriculture at the Humane Society of the United States.

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  • carolyngail

    Speaking of thyroid I don’t see information on your site about hypothyroidism . I am in my late 60′s and have always led a very active, healthy lifestyle and eat mainly a plant based low glycemic diet with very little if any sweets and moderate unrefined carbs. Have never had an overweight problem and was always skinny as a kid and could eat anything I wanted without gaining an ounce.
    I put on 20 lbs. during the past 5 years and no matter how much I diet or exercise the scale doesn’t move. Tests show that my thyroid is low and I was put on synthroid which after taking for several months hasn’t shown to be effective . I’ve kept a diet diary and even on a 800-1000 calories a day I still can’t lose weight. I get at least 30 minutes of exercise a day by walking and lifting weights. I have plenty of energy and am in otherwise good health -having never been hospitalized for anything serious other than having 3 children . Any suggestions ?

    • dr jaya

      in ur case,the dosage of synthyroid is to be increased depending on ur TSH levels…

  • Veviell

    … and OMG Genetically Modified Organism?

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