Thyroid patients can’t manage their condition through diet. However, eating the wrong foods or taking the wrong supplements can cause trouble.
Among the foods that thyroid patients should go easy on — if not avoid altogether — are soy, kelp and dietary supplements like iodine and selenium, says endocrinologist Christian Nasr, MD. “There is a lot of literature on what people shouldn’t do,” Dr. Nasr says.
Should thyroid patients limit these foods?
Soy? If you have hypothyroidism, yes. Eating too much soy causes problems only for those with hypothyroidism, which occurs when your thyroid gland does not make enough thyroid hormones, Dr. Nasr says. The main problem is that soy hinders absorption of the hormones such patients are taking. “Some studies show that if you eat a lot of soy, or drink a big glass of soy milk, within one hour of taking a thyroid hormone, it might affect absorption,” he says. “A lot of people depend on those hormones to achieve a steady state.
“Generally, experts recommend that patients who have a borderline thyroid, one that’s a little underactive but you’re still trying to preserve thyroid function, not to consume soy every day,” he adds. “Don’t eat edamame every day. Don’t drink soy milk every day.”
Turnips, cauliflower and root vegetables? No. Turnips and cauliflower are sometimes thought to cause thyroid problems, but that’s not the case, Dr. Nasr says. They are good for your diet, regardless of any thyroid issues.
One root vegetable that is the exception, and which can negatively impact an underactive thyroid is cassava, a common staple in certain parts of Africa. This plant “is known to produce toxins that can slow an already underactive thyroid,” Dr. Nasr says. But, “that’s not relevant here in the United States, unless you cook cassava and you eat it every day.”
Kelp? No, but don’t take it in supplement form. Thyroid patients should not have more than an average daily recommended intake of 158 to 175 micrograms of kelp per day, Dr. Nasr says. The concentration of kelp in foods is generally not enough to cause a problem. But a kelp capsule can contain as much as 500 micrograms, he says. “Those recommendations to go easy on kelp are for people who don’t understand and take three capsules per day. If you eat kelp once a day, that’s not a problem.”
Cabbage and cruciform veggies? Yes. Even though they are good for us, cabbage and other cruciform vegetables eaten in large quantities, especially in the context of iodine deficiency or borderline iodine levels, can result in hypothyroidism. These vegetables generate an ion that competes with the uptake of iodine by the thyroid.
Should thyroid patients avoid taking these supplements?
Iodine? Yes. Avoid it as a supplement whether you have hyperthyroidism or hypothyroidism. The effect of iodine supplements can vary by the person, causing the thyroid to produce either too much or too little hormone.
Certain alternative medicine websites or doctors tell patients that iodine is “good for your thyroid,” Dr. Nasr says, but “if there is anybody who shouldn’t take iodine,” it is thyroid patients.
Such claims are made because iodine deficiency is the No. 1 cause of thyroid conditions in the world, he says, “but not in the U.S., where we have iodine in our diets.” Iodine is added to many foods, and not just salt, Dr. Nasr says.
He assures patients not to worry that you are getting too much from everyday foods either because the amount of iodine is still limited. “You would have to eat a ton of it to cause problems,” he says. “It’s not, ‘don’t eat anything with iodine.’ It’s, ‘don’t eat a bunch of iodine.’ Patients should be careful with iodine-concentrated supplements.”
Selenium? No, but don’t go over 200 milligrams/day. This supplement is not something you would typically find at the grocery store, but an alternative medicine doctor might prescribe it, Dr. Nasr says. Selenium is OK to use “as long as you’re not overdoing it,” he says. “You should keep it at 200 micrograms per day.”