How To Eat For a Healthy Thyroid
In 2009, I learned quickly the power of the thyroid. After a gut infection triggered aggressive autoimmunity to my thyroid, my health flipped on a dime. My fatigue and brain fog made it hard for me to keep up with my college studies (which was especially distressing with my 3.9 GPA!). The volume of my hair decreased noticeably, and I gained 15lbs in 3-4 months (I’m only 5’2″, so this was a 2 pant size difference!). Eventually, I discovered I had Hashimoto’s and got on thyroid medication, and I learned how to eat for a healthy thyroid. A lot of my symptoms normalized (though not all, which is why I went back to school to study functional medicine).
How could one body part make such an impact? The thyroid gland is a butterfly-shaped organ that sits at the front of the neck. Its main job is to produce thyroid hormones like T4 and T3 that help regulate almost every cell in your body. T3 basically goes around and turns on the light switch in every cell so that work can get done. This is why it’s important to test not just TSH but also free T4 (fT4), free T3 (fT3), and occasionally thyroid antibodies to detect any issues. A healthy thyroid supports a healthy body in every way, so you should know if you have a healthy thyroid!
Unfortunately, there are numerous factors that can negatively impact the thyroid, nutrition being the most notable. (1) It’s important to choose foods to support the thyroid, especially if you’re susceptible to common thyroid diseases like Hashimoto’s, the main cause of low thyroid (my podcast will help you discover if you have a thyroid issue).
Goitrogens are foods that can lead to “goiter”, or swelling of the thyroid gland. This happens by interfering with the thyroid’s uptake of iodine. Since iodine is necessary to produce thyroid hormones, a dangerous domino effect is kickstarted. In light of iodine deficiency, the thyroid keeps growing to keep up with hormonal demands. The most notable goitrogenic rich foods include cruciferous vegetables like broccoli, brussels sprouts, cabbage, kale, arugula, cauliflower, and radish. (2)
Moderate intake of cruciferous veggies doesn’t appear in research to be a problem even for those experiencing thyroid issues. However, over-consumption can potentially lead to harmful effects. So don’t go drinking cabbage juice, eating cauliflower crackers and pizza crust daily, or adding 2 salads’ worth of kale to your green smoothie.
For safe daily consumption, boiling and steaming is great. Moist cooking denatures many of the harmful goitrogenic compounds. (3) Just keep it to 1-2 servings per day and be careful with processed versions, which make it harder to detect how much you’re truly eating.
Soy has gotten a bad reputation, especially when it comes to thyroid health. There is concern that high levels of soy intake can increase risk of thyroid issues and alter thyroid hormone levels. However, recent science reveals that soy’s effects on thyroid function depends on several factors. Rat studies have shown that development of hypothyroidism when consuming soy is largely dependent on iodine status, suggesting that iodine deficiency combined with soy is associated with hypothyroidism. (4)
Furthermore, a clinical trial with Chinese post-menopausal women fed whole soy flour or a soy-derived compound found no significant differences in thyroid markers after 6 months compared to a placebo group. (5) Similarly, another study found no correlations between increased urinary isoflavones (soy derivatives) and fT4 or TSH levels in pregnant women, suggesting that soy consumption is safe in pregnancy as well. (6) This conclusion is especially important because they used a urinary marker of soy consumption, so the results aren’t influenced by people’s memory of what they ate.
The final nail in the coffin of the soy-thyroid scandal: a recent review of 18 studies showed that soy supplementation had no effect on fT3 or fT4 levels and only modestly raised TSH levels. (7)
Considering that soy can potentially offer benefits ranging from prostate and breast cancer protection to cognitive support and heart health, excluding all soy foods for all people with thyroid issues is unnecessary. (8) That being said, it can put a strain on the thyroid gland when there’s iodine deficiency or when consuming very high levels of its isoflavones (9). It is also high in heat-resistant lectins, contributing to it being a common allergen, food sensitivity, and gut irritant. So just like with other potentially inflammatory foods, eliminate it then reintroduce it to see how it individually affects you.
To summarize: eat organic, minimally processed soy every now and then. Just make sure you’re getting enough iodine (frequent fish consumption and a good multivitamin) and you’ve tested your own tolerance to it (with elimination diet and/or labs).
Gluten and Dairy
Gluten is a component of wheat and other grains. It is one of the top most problematic foods for having a healthy thyroid. This is thought to be because the gluten protein looks a lot like thyroid protein, so the immune system can confuse the two in a process called molecular mimicry.
This connection goes both ways. Studies show an increased risk for serious gluten intolerance in those with Hashimoto’s. (10) In fact, one study showed that the higher the thyroid medication needed, the higher the antibodies to gluten were in patients’ blood. (11) Likewise, gluten can negatively impact thyroid health in various ways including contributing to a leaky gut leading to Hashimoto’s, increasing damage from pro-oxidants, and decreasing cellular health. (12)
As further evidence, several studies have shown the beneficial effects of gluten-free diets in supporting thyroid function in Hashimoto’s. Specifically, one showed decreased (more normal) TSH and antibodies and increased fT4 with a gluten free diet in Hashimoto’s patients. (13) Another found that a gluten-free diet for 6 months reduced antibody levels and even slightly increased vitamin D levels in women with Hashimoto’s. (14)
If you’ve tried going gluten-free and haven’t achieved the results you’re hoping for, dairy might be the hidden culprit. In one study, dairy created a strong inflammatory response in 50% of those who are reactive to gluten. (15)
This could be because the casein protein in cow’s milk looks similar to the gluten protein in wheat, which we discussed earlier looks like thyroid protein. The more inflamed the body is, the less likely it’ll take the time to figure out which is which and just attack the thyroid gland. In fact, a survey of more than 2,000 Hashimoto’s patients conducted by thyroid expert Dr Izabella Wentz found that 80% of them felt better when eating dairy-free. So, replacing the cream, yogurt, and cheese for non-dairy alternatives could be a worthwhile effort as well.
Yet another health food to make this list! Flaxseed and cassava fermentation in the gut releases thiocyanates, which interfere with iodine uptake by the thyroid. Fortunately, this can be reduced by eating them with a full meal, having a healthy gut, and heating the foods. Cooking flax should be done by steaming or microwaving rather than baking to avoid the high temperatures that ruin the fragile oils. (16)
In addition, you’d need to consume more than 31g (2 tbsp) of ground flaxseed or 50g of cassava flour (about 2 tortillas) or both at the same time to start getting close to a level that could have a measurable negative impact. (17) With much higher intakes of flax, a study of pregnant rats found significant hypothyroidism in their offspring. (18)
In conclusion, limit flax (and cassava) to a max of 1 serving per day, and eat them gently cooked. Just make sure to purchase cold-milled flaxmeal rather than whole seeds, as the low heat in the processing preserves the fragile oil while also reducing the cyanide by at least half. (19)
Mercury and Fluoride
The heavy metal mercury is an endocrine disruptor, meaning it alters hormones levels, including the thyroid. (20) It has also been linked to significantly increased risk of autoimmune disease, such as Hashimoto’s. Relative to women with the lowest mercury levels (≤0.40 μg/L), women with mercury >1.81 μg/L (upper quintile) were 2.2x more likely to be positive for thyroid antibodies. (21) We can be exposed to mercury by eating too much toxic fish, dental amalgam fillings (and inappropriate removal of them), vaccines, cosmetics, and plastic toys. A good summary of which fish to eat to keep mercury down is the “Best Choices” category from the FDA.
Fluoride in our water, tea, and dental products can also be a big issue for thyroid function. Fluoride can compete with iodine for absorption and usage. A study showed women with increased intake of fluoride from water and diet had more hypothyroidism. (22) In fact, a long time ago fluoride was used a medication to stop hyperthyroidism due to its ability to slow thyroid hormone production by inhibiting iodine. (23)
This means fluoride’s effects are stronger in people with low iodine status, such as those with diets low in seaweed, fish, and eggs. Even low to moderate exposure to fluoridated water leads to signs of hypothyroidism. The higher the fluoride in kids (verified with increased urinary fluoride), the lower the T4 and T3, leading to lower IQ. (24)
However, the answer isn’t just to increase the iodine to try to neutralize the fluorine. Studies in areas exposed to both high iodine and high fluorine show increased goiter (inflamed thyroid), decreased TSH and thyroid uptake of iodine, and decreased IQ, concluding:
“These results indicate that high iodine and high fluorine exert severe damage.” (25)
Consuming nutrient dense whole foods or supplements are vital for maintaining a healthy thyroid. Here’s some of the most important nutrients to focus on:
- Zinc helps T4 (storage hormone) to be converted to T3 (active hormone). (26). In addition, it regulates production of hormones from the brain (hypothalamus and pituitary) that triggers the thyroid to make thyroid hormones, such as thyrotropin-releasing hormone or TRH. Rats given a diet low in zinc were shown to not only have lower thyroid hormones, but also to have lower TRH. (27) Normally, TRH is supposed to increase when T3 decreases in order to help the thyroid make more hormone and get back on track. But zinc deficiency prevents the body from responding normally, therefore increasing the low thyroid state. Food rich in zinc are beef, cashews, hemp seeds, and legumes.
- Selenium is an essential mineral and intricately involved in thyroid hormone production. It not only helps iodine get used, but like zinc, it also helps convert T4 to T3. Indirectly, it supports a healthy thyroid by neutralizing cell damage and decreasing inflammation. This is because the body’s most vital enzymes that produce protective antioxidants are selenium-dependent. In a study on Hashimoto’s patients, supplementation with inositol combined with 83 mcg selenium for 6 months not only improved TSH and thyroid antibodies, but also enhanced thyroid hormones and wellbeing. (28) In another study, thyroid antibodies lowered by 46% after 3 months and 55% after 6 months of 200 mcg selenomethionine supplementation. (29) Selenium supplementation can even help to protect women from developing postpartum thyroiditis. (30) Brazil nuts and fish are good sources.
- Iron is necessary for the enzyme thyroid peroxidase to do its job of assembling iodine to produce thyroid hormones. (31) Iron deficiency can affect the thyroid’s ability to produce hormones as well the body’s ability to regulate them. (32) You can get iron from red meat, poultry, and legumes.
- Protein provides the building blocks for thyroid hormones, and for the antioxidant enzymes mentioned above. Higher levels of certain aminos acids from a variety of high protein foods are associated with higher T4 hormones (33). In addition, zinc, selenium, and iron are more concentrated in high protein foods.
Eating for a healthy thyroid means being careful with gluten, dairy, high mercury fish, and fluoridated water. It also means moderating cruciferous vegetables, soy, and flax while eating a diet rich in foods with zinc, selenium, iron, and protein. If you’d like to test your thyroid to review with your doctor or us, order your labs here. You can improve thyroid function and Hashimoto’s symptoms with the power of nutrition!
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- The role of micronutrients in thyroid dysfunction. 2020. https://pubmed.ncbi.nlm.nih.gov/32528196/
- Goitrogenic Foods and Thyroid Health. 2018. https://kresserinstitute.com/goitrogenic-foods-and-thyroid-health/
- Preliminary observations on the effect of dietary brussels sprouts on thyroid function. 1986. https://pubmed.ncbi.nlm.nih.gov/2419242/
- Goitrogenic and estrogenic activity of soy isoflavones. 2002. https://pubmed.ncbi.nlm.nih.gov/12060828/
- The 6-month effect of whole soy and purified isoflavones daidzein on thyroid function-A double-blind, randomized, placebo controlled trial among Chinese equol-producing postmenopausal women. 2021. https://pubmed.ncbi.nlm.nih.gov/34494323/
- Effects of dietary soy intake on maternal thyroid functions and serum anti-thyroperoxidase antibody level during early pregnancy. 2011. https://pubmed.ncbi.nlm.nih.gov/21314363/
- Systematic Review and Meta-analysis on the Effect of Soy on Thyroid Function. 2019. https://pubmed.ncbi.nlm.nih.gov/30850697/
- The health effects of soy: A reference guide for health professionals. 2022. https://pubmed.ncbi.nlm.nih.gov/36034914/
- Inactivation of thyroid peroxidase by soy isoflavones, in vitro and in vivo. 2002. https://pubmed.ncbi.nlm.nih.gov/12270219/
- Autoimmune thyroid diseases and coeliac disease. 1998. https://pubmed.ncbi.nlm.nih.gov/9872614/
- IgA and IgG antigliadin, IgA anti-tissue transglutaminase and antiendomysial antibodies in patients with autoimmune thyroid diseases and their relationship to thyroidal replacement therapy. 2003. https://pubmed.ncbi.nlm.nih.gov/12625811/
- Adverse effects of gluten ingestion and advantages of gluten withdrawal in nonceliac autoimmune disease. 2017. https://pubmed.ncbi.nlm.nih.gov/29202198/
- Whether a Gluten-Free Diet Should Be Recommended in Chronic Autoimmune Thyroiditis or Not?-A 12-Month Follow-Up. 2021. https://pubmed.ncbi.nlm.nih.gov/34362024/
- The Effect of Gluten-Free Diet on Thyroid Autoimmunity in Drug-Naïve Women with Hashimoto’s Thyroiditis: A Pilot Study. 2019. https://pubmed.ncbi.nlm.nih.gov/30060266/
- Mucosal reactivity to cow’s milk protein in coeliac disease. 2007. https://pubmed.ncbi.nlm.nih.gov/17302893/
- Flaxseed-a potential functional food source. 2015. https://pubmed.ncbi.nlm.nih.gov/25829567/
- Bioavailability of cyanide after consumption of a single meal of foods containing high levels of cyanogenic glycosides: a crossover study in humans. 2016. https://pubmed.ncbi.nlm.nih.gov/25708890/
- Maternal flaxseed diet during lactation programs thyroid hormones metabolism and action in the male adult offspring in rats. 2011. https://pubmed.ncbi.nlm.nih.gov/21448850/
- Reduction of Cyanogenic Compounds in Flaxseed (Linum usitatissimum L.) Meal Using Thermal Treatment. 2013. https://www.tandfonline.com/doi/full/10.1080/10942912.2011.608914
- The endocrine disruptive effects of mercury. 2000. https://pubmed.ncbi.nlm.nih.gov/21432482/
- Mercury and thyroid autoantibodies in U.S. women, NHANES 2007-2008. 2012. https://pubmed.ncbi.nlm.nih.gov/22280926/
- Fluoride exposure and hypothyroidism in a Canadian pregnancy cohort. 2023. https://pubmed.ncbi.nlm.nih.gov/36764861/
- Effect of fluorine on thyroidal iodine metabolism in hyperthyroidism. 1958. https://pubmed.ncbi.nlm.nih.gov/13587625/
- Thyroid function, intelligence, and low-moderate fluoride exposure among Chinese school-age children. 2020. https://pubmed.ncbi.nlm.nih.gov/31698198/
- [Effects of high iodine and high fluorine on children’s intelligence and the metabolism of iodine and fluorine]. 1994. https://pubmed.ncbi.nlm.nih.gov/7859263/
- The Role of Zinc in Thyroid Hormones Metabolism. 2019. https://pubmed.ncbi.nlm.nih.gov/30982439/
- Zinc deficiency, chronic starvation, and hypothalamic-pituitary-thyroid function. 1980. https://pubmed.ncbi.nlm.nih.gov/7405879/
- Myo-inositol plus selenium supplementation restores euthyroid state in Hashimoto’s patients with subclinical hypothyroidism. 2017. https://pubmed.ncbi.nlm.nih.gov/28724185/
- Effects of a six month treatment with selenomethionine in patients with autoimmune thyroiditis. 2003. https://pubmed.ncbi.nlm.nih.gov/12656658/
- The influence of selenium supplementation on postpartum thyroid status in pregnant women with thyroid peroxidase autoantibodies. 2007. https://pubmed.ncbi.nlm.nih.gov/17284630/
- The impact of iron and selenium deficiencies on iodine and thyroid metabolism: biochemistry and relevance to public health. 2002. https://pubmed.ncbi.nlm.nih.gov/12487769/
- Selenium, Iodine and Iron-Essential Trace Elements for Thyroid Hormone Synthesis and Metabolism. 2023. https://pubmed.ncbi.nlm.nih.gov/36834802/
- Effect of Micronutrients on Thyroid Parameters. 2021. https://pubmed.ncbi.nlm.nih.gov/35140907/
- The importance of nutritional factors and dietary management of Hashimoto’s thyroiditis. 2020. https://pubmed.ncbi.nlm.nih.gov/32588591/