It’s true that what you eat can affect your thyroid gland, for better or worse. But some people have long lists of foods they won’t eat, and some people avoid perfectly healthy foods altogether, when they could be eating moderate amounts without an adverse effect on thyroid function. Here’s what you need to know to make better food choices for your thyroid.

Cruciferous vegetables (cabbage, Brussels sprouts, broccoli, kale, cauliflower, turnips, bok choy and others) are generally considered super-healthy foods. They help prevent cancer. In fact, they help to prevent thyroid cancer. Concerns about potential effects of cruciferous vegetables on thyroid function come from findings that they can potentially interfere with thyroid hormone synthesis or compete with iodine for uptake by the thyroid. However, this only seems to happen if consumed in very large quantities and if you are iodine-deficient. The benefits of cruciferous vegetables are clear, and there appear to be no risks at an intake of about 5 ounces (one or two servings) a day. Cooking the vegetables significantly reduces their thyroid-inhibiting effect. I also suggest that you make sure you get enough iodine by eating iodized salt or seaweed, or taking supplemental iodine.

Gluten, a protein found in wheat, barley and rye, has been associated with autoimmune thyroid disorder (AITD) such as Hashimoto’s or Grave’s disease. The link is strong enough that researchers suggest that all people with AITD be screened for gluten intolerance, and that people with gluten antibodies be screened for AITD. It’s basically a case of mistaken identity–the gluten protein is similar to thyroid gland protein, and, if it gets into your bloodstream, can trigger an immune response that attacks your thyroid.

This is why I recommend that you avoid gluten if you have AITD, regardless of whether tests show an active antibody response. There are no nutrients in gluten-containing foods that you can’t get from foods that don’t contain gluten. In addition to corn and rice, gluten-free options include amaranth, millet, quinoa, sorghum, teff, buckwheat, potatoes, and sweet potatoes.The good news is that if you have AITD and are gluten-intolerant, removing gluten completely from your diet can dramatically improve your health.

Soy is tricky. Research findings are mixed. Soy definitely can negatively affect thyroid hormone function in a number of ways, especially in people who are iodine-deficient or already have low thyroid function. But research also suggests that most people can consume up to 30 grams a day of soy protein from traditional soy foods without adverse effects on thyroid function. (That’s about 1 1/2 cups of firm tofu or 1 cup of tempeh.) Other soy products, like meat substitutes and soy protein powders, can be high in soy protein, so check labels and avoid soy protein concentrate or soy protein isolate.

Fiber. Low thyroid function isn’t a good reason to avoid high-fiber foods like beans or root vegetables, or even to avoid taking a fiber supplement if you need it; Just don’t take thyroid meds at the same time. Fiber only interferes with the absorption of thyroid medications. It doesn’t affect your thyroid in other ways.

Bosetti C, Negri E, Kolonel L, et al: A pooled analysis of case-control studies of thyroid cancer. VII. Cruciferous and other vegetables (International). Cancer Causes Control 2002;13:765-775.

8. Dal Maso L, Bosetti C, La Vecchia C, et al: Risk factors for thyroid cancer: an epidemiological review focused on nutritional factors. Cancer Causes Control 2009;20:75-86.

McMillan M, Spinks EA, Fenwick GR: Preliminary observations on the effect of dietary brussels sprouts on thyroid function. Hum Toxicol 1986;5:15-19.