Generally, there's no diet to help with underactive thyroid — a condition that's also called hypothyroidism. You may see lots of claims about hypothyroidism diets. But there's no evidence that eating or avoiding certain foods will help the thyroid work better in people with underactive thyroid.

Getting enough iodine in the diet is essential for the thyroid to work as it should. In developed countries, thyroid disease that comes from not getting enough iodine has been nearly eliminated by adding iodine to salt and food. Eating a balanced diet makes taking extra iodine unnecessary. In fact, too much iodine can cause overactive thyroid in some people. That condition is called hyperthyroidism.

Other supplements such as soy, taken in large amounts, may have an impact on how much thyroid hormone the body makes. But if you get enough iodine in your diet, those supplements won’t cause hypothyroidism.

Eating a balanced diet will keep the thyroid healthy. If you have concerns, talk with your healthcare team about taking a multivitamin with minerals.

If you have underactive thyroid, take thyroid hormone replacement medicine as directed by your healthcare professional. This medicine usually should be taken on an empty stomach. Too much fiber in your diet can keep the body from absorbing the medicine. Some foods, supplements and medicines can have the same effect.

Don’t take your thyroid hormone at the same time as:

• Walnuts.
• Soybean flour.
• Cottonseed meal.
• Iron supplements or multivitamins containing iron.
• Calcium supplements.
• Antacids that contain aluminum, magnesium or calcium.
• Some ulcer medicines, such as sucralfate (Carafate).
• Some cholesterol-lowering drugs, such as those containing cholestyramine (Prevalite, Locholest) and colestipol (Colestid).

To avoid possible problems, eat these foods or use these products several hours before or after you take your thyroid medicine.

Supplements containing biotin, common in hair and nail products, can make it hard to measure how much thyroid hormone is in the body. Biotin does not affect thyroid hormone levels. But supplements that have biotin should be stopped for at least a week before measuring thyroid function so that the measurement is correct.

If you have questions about how to take your thyroid hormone replacement medicine or about your diet, talk with a member of your healthcare team.