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?
The main job of the thyroid, a butterfly-shaped gland at the base of the neck, is to glean iodine from your diet to produce thyroid hormones, which support almost every important 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 some form of thyroid disease. The gland is over- or under-active, according to the American Thyroid Association. More than half don’t know it, which is why everyone should use caution when it comes to these foods. Check out these hidden dangers of a “normal” thyroid.
Kelp and seaweed
Kelp and other seaweeds are considered green superfoods, but these ocean plants are no friend to the thyroid gland. Although extremely rich in iodine, they can throw your iodine levels out of whack. “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. “And in general endocrinologists are telling people with established thyroid disease to be careful about eating kelp and other seaweed.”
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Oh, the irony: Here’s 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. “Even though they’re 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,” writes endocrinologist Christian Nasr, MD of the Cleveland Clinic. 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 MPH, RD, a dietitian and nutrition coach. Here are some health conditions you can blame on your thyroid.
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 hormones patients are taking,” writes Dr. Nasr. “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.” And avoiding soy is becoming more difficult, too.” The problem with soy is a relatively recent one. “Soy has been safely used for thousands of years as a condiment,” says Harris. “But now it’s in soy milk, vegan burgers, protein bars, and shakes. It’s not uncommon to see people eating soy at breakfast, lunch, and dinner.” And unlike the goitrogens in cruciferous vegetables, the compounds in soy can’t be destroyed by cooking.