How Your Diet Could Affect Your Thyroid

If you have an underactive thyroid, diet and meal planning is crucial.

How Your Diet Could Affect Your Thyroid

Medically reviewed in January 2020

Updated on March 1, 2021

If you’ve been diagnosed with an underactive thyroid, or hypothyroidism, you may have heard that the foods you eat could affect your thyroid condition, or that certain foods or supplements may interact with your thyroid medicines. While there’s no specific “thyroid diet,” there are a few things that people with hypothyroidism should know. 

Yes, it’s true that there are certain foods that may affect the thyroid—particularly soy, coffee, walnuts, and fiber-rich foods—because they can reduce the body’s ability to absorb thyroid replacement medication. But here’s the good news: Timing your meals around your medication schedule can help you avoid potential issues, according to Ahmet Ergin, MD, an endocrinologist affiliated with St. Lucie Medical Center in Port St. Lucie, Florida. 

Spacing out thyroid medication and foods 
Unlike some medications that should be taken with meals, thyroid hormone pills should not be taken with food or supplements. 

“It’s a shy medication. It wants to be alone,” Dr. Ergin explains. So how long should you wait after taking thyroid pills before you can eat? Ergin recommends a two-part rule of thumb: 

  • First, take the medication on an empty stomach, and if possible, wait at least one hour before eating. Foods rich in iron, fiber or calcium, such as calcium-fortified juice, red meats, liver, lentils or broccoli, can reduce the body’s absorption of these drugs. If you choose to eat these foods, it’s a good idea to wait even longer—at least two hours after taking your thyroid medicine. 
  • Secondly, wait several hours after taking your medication before having any calcium or iron supplements. The American Thyroid Association (ATA) calls a four-hour separation between medication and supplements “traditional, but untested.” Keep in mind, however, that it’s important to talk to your healthcare provider (HCP) before taking any dietary supplements to find out if they are safe and appropriate for you. 

What about thyroid pills and other meds? 
Thyroid medication is best absorbed in an acidic environment, which means that it doesn’t pair well with antacids, Ergin notes. It’s important, therefore, to wait several hours after taking thyroid medication before taking an antacid that contains aluminum, magnesium or calcium. 

You should also let several hours pass between taking thyroid pills and some ulcer medications, such as sucralfate (Carafate, ProThelial and Orafate) or certain cholesterol-lowering drugs, including cholestyramine (Prevalite and Questran) and colestipol (Colestid).   

It’s important to discuss all possible medication interactions with your HCP. Certain antibiotics, for example, could increase or decrease absorption of your thyroid medicine. 

Eating right for your thyroid 
There’s no evidence that any particular diet will improve thyroid function in people with hypothyroidism. “We don’t put people with hypothyroidism on a diet,” Ergin says. “There is no diet proven to improve the progression of disease. You don’t have to change your whole life.” 

That said, it’s still important to be mindful of what you eat. Be sure to follow a healthy diet that emphasizes fiber and nutrient-rich fruits and vegetables, nuts and complex carbohydrates as well as lean protein. Choose foods with unsaturated fats, such as olive oil, fatty fish and seeds. Meanwhile, limit your intake of processed products and foods high in salt, sugar and unhealthy saturated fats. 

Cauliflower and soy aren’t the enemy 
Despite what you may have heard, you don’t need to strictly steer clear of soy—just avoid eating it too soon before or after taking your thyroid replacement medication, Ergin points out. Eating large amounts of soy could reduce thyroid hormone production because it has antithyroid effects. (An iodine deficiency worsens these effects while iodine supplementation helps offset them.) But it’s important to understand that people who don’t have an iodine deficiency won’t develop hypothyroidism from eating soy. Soy intake is mainly an issue among babies with congenital hypothyroidism who are fed soy-based formulas, Ergin explains. This issue, however, is uncommon since iodine has been added to soy-based formulas since the 1960s. 

You may also think you should steer clear of biotin, a substance found in some supplements as well as in some hair and nail products. Biotin actually does not alter thyroid hormone levels, but it can make measurements inaccurate. So, it’s a good policy to stop taking it at least one week before your thyroid blood test if you are taking more than 5,000 micrograms (mcg) of biotin daily. 

It’s commonly believed that cruciferous vegetables are bad for your thyroid as well. For most people being treated appropriately for hypothyroidism, however, there is no need to avoid eating these foods, which include cabbage, cauliflower, broccoli, Brussels sprouts, bok choy and kale. In animals fed very high amounts of cruciferous vegetables, hypothyroidism can develop. But in studies involving people, a similar effect was detected only in those with an iodine deficiency. 

So, what about iodine? 
It’s true: Having an iodine deficiency can devastate thyroid function. This may tempt you to be proactive about your health and try a supplement but, odds are, you’re getting all the iodine you need through your diet alone. In the United States, iodine deficiency hasn’t been a major cause of hypothyroidism for many years, thanks to initiatives from the 1920s that added iodine to salt. But keep in mind, sea salt contains only a small amount of iodine. If you prefer to use sea salt in your cooking, you don’t have to give it up entirely, but you may want to include some regular iodized table salt in your diet as well.   

Taking iodine supplements, meanwhile, could not only be unnecessary but also risky, doing more harm than good, Ergin says. “I think most people have the belief that if they take iodine it will help them,” he says. “But we see overdose because of iodine supplements.” Ergin adds that high iodine intake could lead to thyroiditis, or inflammation of the thyroid gland. 

Although excessive intake of iodine from supplements could alter your thyroid hormone level, iodine-rich foods, such as milk, most seafood, eggs and soy products are reasonable to consume.    

Possible exceptions to this rule are expectant and nursing mothers. These women may benefit from taking a daily iodine supplement or a prenatal vitamin that contains iodine since the recommended dietary allowance for the mineral increases during pregnancy. If you’re pregnant or breastfeeding, talk to your HCP to determine if a supplement is safe and appropriate for you. 

Be cautious about selenium 
Selenium is necessary for a healthy thyroid but skip the supplement unless it’s recommended by your HCP. Taking too much of this essential element could make you sick. The recommended daily value for those age 14 and older is 55mcg (pregnant and nursing women need slightly more). In the U.S. however, the average adult is getting about twice as much as they need, making selenium deficiency rare. 

And remember: Selenium-rich foods are all around us, including tuna, tofu, pork chops and nuts. In fact, just one chopped-up Brazil nut sprinkled onto your smoothie or oatmeal will give you roughly 90mcg, or more than a day’s worth.

Sources:  

National Library of Medicine. “LABEL: LEVOTHYROXINE SODIUM tablet.” 
Jacqueline Jonklaas, Antonio C. Bianco, Andrew J. Bauer, et al. “Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement.” Thyroid. Vol. 24, No. 12. 
The National Academy of Hypothyroidism. “How to Take Your Thyroid Medication Properly.” 
Deborah Chon, Tamar Reisman, Jane Weinreb, et al. “Concurrent Milk Ingestion Decreases Oral Levothyroxine Absorption.” ENDO 2017 Annual Meeting. 
Mayo Clinic. “Hypothyroidism diet: Can certain foods increase thyroid function?” 
Harvard Medical School. “Healthy eating for a healthy thyroid.” 
S C Conrad, H Chiu, B L Silverman. “Soy formula complicates management of congenital hypothyroidism.” Archives of Disease in Childhood. 2004;89:37-40. 
Office of Dietary Supplements. “Iodine.” 
Oregon State University. “Cruciferous Vegetables.” 
Mayo Clinic. “Mayo Clinic Q and A: Sea salt and sufficient iodine intake.” 
American Thyroid Association. “Iodine Deficiency.” 
American Thyroid Association. “Thyroiditis.” 
Office of Dietary Supplements. “Selenium.” 

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