Q: I was diagnosed with hypothyroidism and have been getting conflicting information on what I should eat and drink. One source said a calcium-rich diet was fine, whereas another said I should limit dairy. I’ve also read that I should avoid soy and iodine. But then a friend told me iodine is helpful. Can you give me some guidance on the best diet to manage my condition?

A: Hypothyroidism — or underactive thyroid — is a condition in which your thyroid gland doesn’t produce enough of certain crucial hormones. If you are diagnosed with hypothyroidism, you should take a thyroid hormone replacement as directed by your health care provider.

Generally, there’s no hypothyroidism diet. Although claims about hypothyroidism diets abound, there’s no evidence that eating or avoiding certain foods will improve thyroid function.

It is true that iodine deficiency can cause hypothyroidism. But in developed countries, including the U.S., thyroid disease from iodine deficiency has been nearly eliminated by iodine additives in salt and food. While some alternative medicine practitioners recommend iodine tablets or kelp supplements — which are high in iodine — for people with hypothyroidism, eating a balanced diet makes taking supplemental iodine unnecessary. In fact, too much iodine can cause hyperthyroidism.

Other supplements such as soy, taken in large amounts, may have an impact on thyroid hormone production but won’t cause hypothyroidism in people who are not also iodine deficient.

Whether people who have hypothyroidism should avoid soy is a topic of debate. Soy has long been thought to interfere with the body’s ability to absorb synthetic thyroid hormone, which most people with hypothyroidism are prescribed. However, there’s no evidence that people who have hypothyroidism should avoid soy completely.

Generally, it’s best to wait four hours after taking thyroid medication to consume any products that contain soy. The same guidelines apply to other products that may impair the body’s ability to absorb thyroid medication, including concentrated iron and calcium supplements, and antacids that contain calcium or aluminum hydroxide.

Calcium itself is not harmful for patients to consume. It is calcium supplements — or antacids containing calcium — that can interfere with the absorption of thyroid hormone replacement medications.

This interference happens chiefly if you take thyroid hormone replacement and calcium supplements at or near the same time. Other supplements — including those containing magnesium and iron — can have the same effect.

In addition, proton pump inhibitors and some cholesterol-lowering drugs may affect absorption.

To prevent potential interactions, use these products several hours before or after you take your thyroid medication.

Additionally, certain foods, such as walnuts, or an excess of dietary fiber, can also impair the absorption of thyroid hormone replacement medication.

The best recommendation for effectively managing hypothyroidism is to take your medication as directed and avoid dietary extremes.

If you have concerns, talk with your doctor about taking a multivitamin with minerals.

— Todd B. Nippoldt, M.D., endocrinology, Mayo Clinic, Rochester, Minnesota

Mayo Clinic Q&A is an educational resource and doesn’t replace regular medical care. Email a question to MayoClinic Q&A @mayo.edu.