“Is your thyroid making you fat?” You’ve probably seen this question popping up all over the media. Provocative headlines aside, more Americans are wondering whether underactivity in their thyroid—a butterfly-shaped gland in the throat that produces metabolism-regulating hormones—may be causing symptoms like fatigue, depression, and yes, weight gain.

The question is a good one. According to the American Association of Clinical Endocrinologists, as many as 25 million U.S. adults (eight out of ten of them female) have hypothyroidism, but only half are aware of it. Still, over the past 20 years, diagnosed hypothyroid cases have steadily increased, thanks partly to more and earlier testing, says Gregory A. Brent, MD, professor of medicine and physiology at the University of California, Los Angeles.

The most common cause of hypothyroidism is likely Hashimoto’s thyroiditis, an autoimmune disease triggered by inflammation of the thyroid gland, but pregnancy- or menopause-related hormone imbalances can also trigger it. Recent studies suggest environmental toxins may also play a role, accounting for as much as 30 percent of thyroid disease risk, says Brent.

Whether you’ve been diagnosed with low thyroid or want to protect against it, here are some natural diet and supplement strategies to help maintain optimal thyroid health.

Next page: Calories, iodine, and vitamin D

Don’t restrict calories

Following a restrictive diet to combat weight gain actually may worsen low thyroid. “Studies clearly demonstrate that [calorie-restrictive] dieting suppresses thyroid hormones and metabolism,” says Kent Holtorf, MD, an expert in endocrinology in Torrance, California, and founder of the National Academy of Hypothyroidism. “The low-thyroid patients I see typically have up to 40 percent lower metabolism than expected for their body mass index [BMI].” And once metabolism slows, it takes significantly more effort to burn calories. Until metabolic abnormalities are corrected, Holtorf says, diet and exercise alone won’t achieve overall health or a healthy weight.

Check iodine levels

Most people with hypothyroidism assume they’re deficient in this mineral, which the thyroid uses to produce hormones. But that’s not always the case. In fact, North Americans tend to overconsume iodine, says Mary Shomon, author of The Thyroid Diet (HarperCollins, 2004). One gram of salt contains 76 mcg (nearly the 100 mcg recommended daily amount) of iodine, and most people consume more than 3 grams of sodium daily. Before supplementing, get tested.

Boost your vitamin D

Produced in the skin by exposure to the sun—and found in fatty fish (such as mackerel, sardines, and salmon), egg yolks, and fortified foods—vitamin D is a cofactor for thyroid hormone production, says Richard Shames, MD, an integrative health specialist in Sebastopol, California, and coauthor of Feeling Fat, Fuzzy or Frazzled? (Hudson Street, 2005). Vitamin D deficiency is extremely common and even more so in people with thyroid disease. To maintain a healthy thyroid, take 1,000–2,000 IU daily—but check with your doctor first, says Shames, who believes the current RDA (200– 600 IU) is far too low.

Next page: iron, anti-inflammatory foods, broccoli, and selenium

Supplement with iron

Fatigue due to low iron levels or anemia may signal an underactive thyroid, says Holtorf, because iron helps activate thyroid hormones. For prevention, eat iron-rich foods such as lean red meats, fish, poultry, and legumes, and consider taking 15–30 mg of elemental iron daily. (Take 30–90 mg daily if you have mild to moderate anemia.) For best absorption, choose a chelated supplement that includes vitamin C.

Choose anti-inflammatory foods

“Anti-inflammatory foods such as fish, olive oil, avocados, and fruits and vegetables may help patients with autoimmune thyroid [marked by swelling of the thyroid],” says Shomon. Avoid inflammation-promoting foods such as white flour and sugars, as well as foods that may contain chemical pesticides or added hormones, she adds.

Cook your broccoli

Certain foods, known as goitrogens, can slow down the thyroid or promote formation of a goiter, or enlarged thyroid. These include brassica and cruciferous vegetables such as brussels sprouts, cabbage, and broccoli. But not to worry, says Shomon. “These can be a problem if eaten in large quantities, and if eaten raw, as in a juice,” she says. When cooked or lightly steamed, most of the veggies lose their goitrogenic potential.

Don’t forget selenium

Found naturally in meat, fish, Brazil nuts, grain products, and mushrooms, the mineral selenium helps with both production of T4 thyroid hormone (thyroxine) in the thyroid gland and its conversion to the active form of T3 (thyronine), explains Shames. The thyroid gland has one of body’s highest concentrations of selenium. Studies have shown that blood levels of selenium decrease with age; digestive conditions such as Crohn’s disease may also cause deficiency. Aim to get about 400 mcg a day (the upper daily recommended limit) from food and supplement sources combined, says Shomon.

Next page: Are common chemicals harming your thyroid?