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The Best and Worst Foods for Your Thyroid

Is there a thyroid diet?

Your thyroid is your body's silent workhorse—most of the time, it functions so smoothly that we forget it's there. But this little, butterfly-shaped gland that sits at the base of your neck helps regulate your metabolism, temperature, heartbeat, and more, and if it starts to go haywire, you'll notice. An underactive thyroid—when the gland fails to produce enough thyroid hormone (TH)—can bring on weight gain, sluggishness, depression, and increased sensitivity to cold. An overactive thyroid, on the other hand, happens when your body produces too much TH, and can cause sudden weight loss, irregular heartbeat, sweating, nervousness, and irritability.

Genetics, an autoimmune condition, stress, and environmental toxins can all mess with your thyroid—and so can your diet, one factor you can completely control. Here are the foods that may help keep your thyroid humming along, as well as some that won't.

Best: Seaweed

Your thyroid needs iodine to work properly and produce enough TH for your body's needs. Don't get enough iodine, and you run the risk of hypothyroidism or a goiter (a thyroid gland that becomes enlarged to make up for the shortage of thyroid hormone). Most Americans have no problem getting enough iodine, since table salt is iodized—but if you're on a low-sodium diet (as an increasing number of Americans are for their heart health) or follow a vegan diet (more on that later), then you may need to up your intake from other sources.

Many types of seaweed are chockfull of iodine, but the amount can vary wildly, says Mira Ilic, RD, a registered dietician at the Cleveland Clinic. According to the National Institutes of Health, a 1-gram portion can contain anywhere from 11% to a whopping 1,989% of your percent daily value. But since seaweed is especially high in iodine, you shouldn't start eating sushi every day of the week. Too much iodine can be just as harmful to your thyroid as too little by triggering (or worsening) hypothyroidism. To get seaweed's big benefits without going overboard, Cynthia Sass, MPH, RD, and Health's contributing nutrition editor advises sticking to one fresh seaweed salad per week (in addition to sushi), and steering clear of seaweed teas and supplements.

Best: Yogurt

Short of eating a few kelp salads, you probably don't have to worry about getting too much iodine from any other foods. In particular, dairy products are full of this nutrient (and in more manageable amounts), according to a 2012 research in the journal Nutrition Reviews. Part of the reason is because livestock are given iodine supplements and the milking process involves iodine-based cleaners. Plain, low-fat yogurt, or Greek yogurt is a good source—it can make up about 50% of your daily intake of iodine.

Best: Brazil nuts

Brazil nuts are packed with another nutrient that helps regulate thyroid hormones: selenium. In one 2003 study by researchers in France, women who consumed higher amounts of selenium were less likely to develop goiters and thyroid tissue damage than those who didn't. Plus, it may also help stave off long-term thyroid damage in people with thyroid-related problems like Hashimoto's and Graves' disease, according to a 2013 review in the journal Clinical Endocrinology.

Just one kernel contains 96 micrograms, which is almost double the daily recommended intake of 55 micrograms. And remember, the max upper limit of selenium is 400 micrograms a day, so don't go overboard. Too much selenium can cause "garlic breath," hair loss, discolored nails, and even heart failure, says Ilic.

Best: Milk

Much of the iodine in the average American diet comes from dairy products, according to a 2008 study by researchers from the Food and Drug Administration. But our consumption of dairy has been on the decline for decades: During the years between 1970 and 2012, there's been a 60-gallon drop, largely because we're drinking milk less often, say the researchers. 

By drinking 1 cup of low-fat milk, you'll consume about one-third of your daily iodine needs. Another good idea: Opt for a glass that's been fortified with vitamin D. One 2013 study found that people with an underactive thyroid (hypothyroidism) were more likely to be deficient in D than their healthier counterparts. (Another honorable dairy mention is cheese, especially cheddar: just one slice is good for 12 micrograms of iodine and 7 IU of vitamin D.)

Best: Chicken and beef

Zinc is another key nutrient for your thyroid—your body needs it to churn out TH. Take in too little zinc, and it can lead to hypothyroidism. But get this: If you develop hypothyroidism, you can also become deficient in zinc, since your thyroid hormones help absorb the mineral, explains Ilic. And when that happens, you may also experience side effects like severe alopecia, an autoimmune condition that attacks hair follicles and makes it fall out in clumps, according to one 2013 report.

You probably get enough zinc already (most people in the U.S. do), but if you have a poor diet or a GI disorder that interferes with your ability to absorb zinc, you might be at risk for a deficiency, says Ilic. Meats are a good source: One 3-ounce serving of beef chuck roast contains 7 milligrams; a 3-ounce beef patty contains 3 milligrams; and a 3-ounce serving of dark chicken meat contains 2.4 milligrams.

Best: Fish

Since iodine is found in soils and seawater, fish are another good source of this nutrient. In fact, researchers have long known that people who live in remote, mountainous regions with no access to the sea are at risk for goiters. "The most convincing evidence we have [for thyroid problems] is the absence of adequate nutrition," says Salvatore Caruana, MD, the director of the division of head and neck surgery in the department of otolaryngology-head and neck surgery at ColumbiaDoctors. 

One 3-ounce serving of baked cod contains about 99 micrograms of iodine — or 66% of your daily recommended intake. Canned tuna is another good option: a 3-ounce serving runs about 17 micrograms, or 11% of your daily iodine quota. (Bonus: One 3-ounce serving of canned yellowfin tuna also contains 92 micrograms of selenium.)

Best: Shellfish

Unless a food is fortified with iodine, the Food and Drug Administration doesn't require manufacturers to list it on their products. That's just one of the reasons why it's hard to know how much of this nutrient is in certain foods, says Ilic. But as a general rule, shellfish like lobster and shrimp are good sources of iodine, she says. In fact, just 3 ounces of shrimp (about 4 or 5 pieces) contains more than 20% of your recommended intake. Bonus: shellfish can also be a good source of zinc, too. Three ounces of Alaskan crab and lobster contain 6.5 and 3.4 milligrams of zinc, respectively.

Best: Eggs

One large egg contains about 16% of the iodine and 20% of the selenium you need for the day, making them a thyroid superfood. If you haven't been instructed otherwise by your doctor, eat the whole egg (try our foolproof trick for cooking eggs over easy)—much of that iodine and selenium is located in the yolk, says Ilic.

Best: Berries

The best diet for your thyroid requires more than just iodine, selenium, and vitamin D, says Ilic. And—perhaps unsurprisingly—foods that are high in antioxidants are also good for your thyroid. One 2008 study by researchers from Turkey suggests that people with hypothyroidism have higher levels of harmful free radicals than those without the condition. 

Berries are chockfull of antioxidants, according to a 2010 study in Nutrition Journal. The researchers examined more than 3,000 foods and found that wild strawberries, blackberries, goji berries, and cranberries ranked especially high.

Best: Love Youself

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Good: Cauliflower, kale, broccoli, bok choy

Do a little Googling, and you might turn up a page or two claiming that cruciferous vegetables can cause thyroid troubles. The truth is a little murkier. While it's true that these veggies contain compounds called glucosinolates, which might interfere with your body's production of thyroid hormones in high amounts, it's pretty unlikely that they'll harm your thyroid if you're eating normal-size servings. One case report in the New England Journal of Medicine highlighted the story of an 88-year-old woman who showed up to the ER with hypothyroidism after eating about 2 or 3 pounds of bok choy a day—but, as Ilic points out, "that's not a normal amount."

Bottom line: "Cruciferous vegetables like cauliflower and kale are important for a healthy diet and a healthy thyroid," says Ilic. (And besides, if you cook down the foods, you'll release enzymes that are related to glucosinolates. See? Problem solved.)

Fine: Soy

Soy for thyroid health is controversial: There's some research that suggests soy might negatively affect your thyroid gland under certain circumstances, like if you have an iodine deficiency. (Something to keep in mind: A 2011 study of vegetarians and vegans in the Boston area found that some vegans did have a mild iodine deficiency, most likely because they don't eat animal and dairy products). But other research presented at the 2014 Endocrine Society's annual meeting found that unless you have thyroid problems already, soy probably won't have any effect on it. Again, says Ilic, as long as you're eating normal amounts of soy, there's no reason to worry it'll hurt your thyroid.

Worst: Gluten (if you have celiac disease)

People with celiac disease—the autoimmune disease that's characterized by an intolerance to the gluten in wheat, barley, and rye—are also more likely to have higher rates of thyroid problems, according to a 2007 report by researchers in the United Kingdom. "Eating a gluten-free diet helps control the symptoms, which may also help protect the thyroid gland," says Ilic. But unless you have celiac disease—and we're not talking an L.A.-aversion to gluten, here — you might not want to avoid breads after all. In fact, thanks to some of the baking processes, bread can actually contain some iodine.

Worst: Processed foods

If you're thinking about upping your intake of salty, processed foods just to fit more iodine into your diet, think again. More than 75% of our dietary sodium intake comes from restaurant, pre-packaged, and processed fare. (In fact, you'd probably be surprised to learn just how many foods are actually just hidden salt traps.) But "manufacturers don't have to use iodized salt in their products," says Ilic. And according to the National Institutes of Health's Office of Dietary Supplements, they "almost never" do. The upshot: You may be taking in too much sodium (which can set you up for high blood pressure, then heart disease), minus the iodine.

Worst: Fast food

Similar to processed foods, fast food chains also aren't required to use iodized salt in their foods. And even when they do, it might not boost the iodine content all that much, according to one 2010 commentary in the journal Endocrine Practice, which tested products from two fast food restaurants in the Boston area. The study authors concluded that drive-thru fare might be pretty low in iodine.