10 Foods that Thyroid Experts Avoid—and 3 that They Love

Updated: Mar. 30, 2021

Some foods touted as nutritional superstars—like kale and millet—might not be the best choices for the health of your thyroid gland.

First, what’s a thyroid?

Your thyroid is a butterfly-shaped gland at the front of your neck. It is tasked with using iodine from your diet to produce thyroid hormones, which support almost every bodily function you can think of—heart rate, circulation, metabolism, your internal clock, liver function—the list goes on and on. An estimated 20 million Americans (and far more women than men) have an over- or under-active thyroid gland, according to the American Thyroid Association. More than half don’t know it, which is a good reason to know the foods that thyroid experts love and those that they avoid. Check out these hidden dangers of a “normal” thyroid.

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Avoid: Kelp and seaweed

Kelp and other seaweeds are considered green superfoods, but these ocean plants are not necessarily a friend to the thyroid gland. “Seaweed is the richest source of dietary iodine,” explains Richard Mack Harrell, MD, an endocrinologist with Memorial Healthcare System in Hollywood, Florida, and a spokesman for the American Association of Clinical Endocrinologists. While that sounds like a good thing, too much iodine could be harmful. Diets that over dose in iodine can cause hyper or hypothyroidism but only if ingested in overwhelmingly large quantities. For example, in one 2014 case study, a woman on a kelp diet ended up with hyperthyroidism (an overactive thyroid) followed by hypothyroidism (an underactive thyroid). “In general endocrinologists are telling people with established thyroid disease to be careful about eating kelp and other seaweed,” says Dr. Harrell. Parsippany, New Jersey-based endocrinologist Cheryl Rosenfeld, DO, also an adjunct clinical associate professor of medicine at the Touro College of Osteopathic Medicine in New York, points out that there is a low-to-no risk of iodine deficiency in the United States since our food supply is enriched. Diets that under-dose iodine can cause goiters and hypothyroidism. In this country that’s unusual unless you are on a very restrictive diet because traditional wheat products are supplemented and other grains are not.

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Avoid: Kale

Kale is another popular health food that may not be the best choice for people with thyroid issues. Kale is a cruciferous vegetable, and all of the vegetables in this category (like cabbage, broccoli, cauliflower, Brussels sprouts, rutabaga) are considered goitrogens—substances that disrupt thyroid function by interfering with how the gland uses iodine, explains Dr. Rosenfeld. “Too many cruciferous vegetables may cause thyroids to become over- or underactive,” she says. Most often these individuals already have undiagnosed thyroid disorders and the surplus of cruciferous veggies tips the scale, she says. Cooking cruciferous vegetables makes them thyroid-safe, but since kale is usually eaten raw—in salads and smoothies, for instance—it may be a problem. “When people are eating big kale salads every day, especially if they’re low in thyroid hormone, it can affect thyroid function,” says Cheryl Harris, RD, a dietitian and nutrition coach in Fairfax, Virginia. Here are some health conditions you can blame on your thyroid

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Avoid: Green juice

Juicing is more than a health craze, it’s a movement, but if you have thyroid issues, this may be one healthy habit to skip, says Dr. Rosenfeld. “When you juice your greens, the goitrogens are even more concentrated,” she says. “Eat at your veggies and fruits rather than drinking them.”

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Avoid: Soy

Estrogen (and soy is a phytoestrogen) increases thyroid hormone-binding globulin which increases bound thyroid hormone and needs for more thyroid hormone. You would have to eat a lot of soy before this became an issue. Soy is another goitrogen, which can be an issue for people whose iodine levels are already compromised. “The main problem is that soy hinders the absorption of the thyroid hormones patients are taking, “says John Woody Sistrunk, MD, an endocrinologist in Jackson, Mississippi, and the Chair of the American Association of Clinical Endocrinologist’s Thyroid Disease State Network. Thyroid hormone should be taken on an empty stomach away from vitamins, iron, calcium, fiber and some of these foods can reduce thyroid hormone absorption.

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Avoid: Gluten

A significant number of people with thyroid disease also have celiac disease, an autoimmune disorder triggered by consuming gluten. This is why many people with thyroid issues think avoiding gluten is worth a try, says Harris. Dr. Rosenfeld and Dr. Sistrunk both caution that there is no evidence to suggest a gluten-free diet has any effect on thyroid function in the absence of celiac disease. Find out the 13 silent signs of a thyroid problem that you should know.

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Avoid: Sugar

The sweet stuff already has a bad enough rap where your health is concerned—now you can add thyroid trouble to the list of grievances. Harris explains that people with thyroid disease are at a higher risk of developing type 2 diabetes and cardiovascular disease, and limiting sugar can help minimize this risk.

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Avoid: Artificial sweeteners

Yes, sugar can be deleterious to your health, but artificial sweeteners may not be any better if you are at risk for thyroid disease. “There are a few recent small studies showing that artificial sweeteners can affect thyroid function,” Harris says. “There haven’t been large-scale studies yet, but there’s some belief that the artificial sweeteners may affect the gut microbiome,” as one published in Trends in Endocrinology and Metabolism suggests.

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Avoid: Specialty salts

The issue here isn’t anything in the salts—it’s what they don’t have: A lot of the table salt available in the United States has been iodized (iodine was added) to help people get enough of the nutrient. But the popularity of kosher and sea salts means some people could be falling short. “The only known use of iodine in the body is to make thyroid hormone,” says Elizabeth N. Pearce, MD, an endocrinologist with Boston Medical Center, and past president of the American Thyroid Association. Don’t miss these healthy habits that make your thyroid happy.

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Avoid: Millet and cassava

Not traditionally used in American cooking, both millet and cassava flours have recently become more popular. “Millet is a grain that used to be used in this country mainly in birdseed,” says Harris. “But it’s getting used a lot more now, particularly as more people go gluten-free. And cassava is a root vegetable used a lot in Central American cooking, but it’s also being used in this country now for flour, and for tortilla chips and other snacks.” Like millet, cassava is also gluten-free—and both are also goitrogens. But neither millet or cassava is likely to cause thyroid issues for people unless they already have low iodine levels or diagnosed thyroid conditions, she says.

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Avoid: Processed foods

“There’s a lot of speculation about why thyroid disease is so common now, and whether the additives and chemicals in processed foods play a role,” says Harris. “There’s some belief that the additives carrageenan and polysorbate 80 are linked to many autoimmune diseases, so it may be an issue with thyroid disease, too. But it hasn’t been extensively studied.” It’s a good idea to avoid processed foods, agrees Dr. Rosenfeld. “Diets that are heavy in processed foods are linked to (type 2) diabetes and heart disease.” Next, find out the thyroid cancer symptoms you shouldn’t ignore.

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Love: Brazil nuts

A one-ounce serving of Brazilian nuts contains a whopping 544 micrograms of selenium, according to the National Institute of Health’s Office of Dietary Supplements. “There is data that tells us if you have Hashimoto’s disease, but your thyroid is still working, it will take a longer time to peter out if you consume adequate amounts of selenium,” says Dr. Rosenfeld, as is suggested by findings published in Clinical Endocrinology. Hashimoto’s disease is an autoimmune disorder that can cause your thyroid to become sluggish.

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Love: Tuna

Tuna and other fish such as sardines are loaded with heart-healthy omega-3 fatty acids, which is why the American Heart Association recommends eating two servings of fish (particularly fatty fish) per week. Tuna and sardines, in particular, are also good sources of selenium. If you want more healthy fats but don’t like fish, check out some other ways to get omega-3s.


Love: Eggs

Another good source of selenium, eggs can help keep your thyroid functioning for a longer period of time. One hard-boiled egg contains 15 micrograms of selenium, according to the USDA. “Multivitamins also contain your daily recommend amount of selenium,” Dr. Sistrunk says. Check out 54 ways to prepare those eggs.