A low iodine diet is prescribed before diagnostic radioactive iodine uptake (RAIU) tests and before radioactive iodine treatments. The RAIU test is an imaging scan used to check thyroid health. Radioactive iodine (RAI) treatment is used to treat thyroid diseases such as hyperthyroidism, Graves disease, and thyroid cancer.

The low iodine diet is a special diet that limits the amount of iodine you can consume through foods and beverages. This article gives an overview of the thyroid gland, RAIU scans, RAI treatment, which foods to avoid and include on a low-iodine diet, and overcoming challenges of the diet.  

Overview

Iodine is a trace mineral or element found in some foods, some types of salt, and dietary supplements. It does not naturally occur in the body so it needs to come from these foods or supplements.

The thyroid gland uses dietary iodine to produce thyroid hormones that regulate metabolism. Thyroid cells are unique because they are the only cells in the body that absorb iodine. Too little or too much iodine can cause or worsen thyroid disease.

A low-iodine diet is necessary when preparing for a radioactive iodine uptake (RAIU) test or treatment. This diet is required “starve” the thyroid of iodine and reduce the amount of resident iodine. Lowering amounts of resident iodine makes the thyroid “iodine hungry.”

When it’s time for the RAIU scan or treatment, you will take radioactive iodine (RAI) in capsule form. RAI uptake into the thyroid cells allows them to be visualized on a diagnostic imaging scan. It can also destroy tumor cells when this therapy is used for thyroid cancer treatment.

Decreased amounts of resident iodine makes it easier for the RAI to get into the thyroid or thyroid cancer tissue.

The low iodine diet may sound simple because you only need to eliminate one mineral from your diet—iodine. But it requires some planning. If you eat a lot of pre-packaged or frozen foods or eat out, you will need to make some significant adjustments while on a diet. 

The Thyroid Cancer Survivors Association provides recommendations regarding which foods are permitted and prohibited when following a low iodine diet. This organization is considered a trustworthy and knowledgeable source of information.

Iodized, Non-iodized, and Kosher Salt

The biggest rule of the diet is to eat foods that are low in iodine. Since most salt is iodized (meaning it has iodine added), you need to avoid iodized salt and foods containing iodized salt. Instead, you can use non-iodized and kosher salt because they do not contain iodine.

Foods to Avoid

Most low-iodine diets take less than 50 micrograms (mcg) of iodine per day. However, it’s best to ask your healthcare provider to ensure you don’t have a different requirement. The following have higher levels of iodine and should be avoided while on a low-iodine diet:

  • Dairy (milk, yogurt, cheese, butter, ice cream, sour cream)Egg yolksSeafood (anything from the ocean, including fish, shellfish, and kelp)Processed foods (pre-packaged foods, frozen dinners, deli meats, hot dogs, bacon, sausage, foods at restaurants and fast-food eateries)Commercial baked goods (commercially baked bread and confections)Soy (includes soybeans, soy sauce, tofu, and any other food with soy)Maraschino cherriesChocolate (milk chocolate contains dairy; some dark chocolates may be allowed—check the label)Red dye #3 (check the label or call the manufacturer)Beans (avoid red kidney beans, navy beans, lima beans, pinto beans, and cowpeas)

Foods to Include 

Don’t be disheartened by the list of foods you cannot eat! There are plenty of foods you can eat. Here are foods that are allowed on the low-iodine diet:

  • Fresh meats (no more than 5-6 ounces a day)Fresh fruits and vegetables (no potato skins)Frozen vegetables without added salt (no rhubarb)Vegetable oilsSodas (as long as they don’t contain red dye #3; check the label or call the manufacturer)Unsalted peanut butter and nutsCoffee and tea (non-dairy creamer is allowed)Matzo (check the label to make sure there is no iodate dough conditioner)Homemade bread (without egg yolks, dairy, or iodized salt in the ingredients)Fresh and dried herbs and spices, including pepperBeer, wine, and distilled alcohols (wine coolers and flavored liquors may contain red dye #3, check the label)Canned peaches, pineapple, and pearsHoneyMaple syrupJams and jelly (without red dye #3)

Challenges

Among the challenges of following a low iodine diet is that you may find conflicting information about which foods are allowed and prohibited on the diet. One source may say that you should only avoid potato skins, while another may suggest that you cannot eat potatoes at all.

Iodine Content of High Iodine Foods

The following values for the foods listed below come from the National Institute of Health (NIH). These values can help guide you when you are estimating the iodine levels of food.

Iodine Content of Low Iodine Foods

Foods lower in iodine:

Confusing information can add to the challenge of this already restrictive diet. Don’t hesitate to ask your healthcare provider for a referral to a nutritionist if you want personalized advice and guidance.

Dining Out

Eating out is almost nearly impossible while following a low-iodine diet. You can’t guarantee what type of salt a restaurant uses in their recipes. Foods served in fast food restaurants are mostly processed and contain salt, so they should be avoided as well.

Tips To Help You Plan Ahead

Here are a few tips to help plan ahead for a low-iodine diet:

Recipes and Cookbooks

When you season your food and cook at home, be sure to use non-iodized salt or kosher salt instead of iodized salt. Try using fresh herbs such as basil or cilantro to liven up your meals. You can prepare a variety of foods as long as the ingredients fit the criteria above.

Cooking can be challenging, even if you are already a good cook because it is hard to learn a new way of preparing food. The Thyroid Cancer Survivors Association offers a low-iodine cookbook that can be downloaded for free. It boasts over 300 low-iodine recipes and is a favorite among low-iodine dieters. 

Summary

The low iodine diet is a special diet that limits the amount of iodine you can consume through foods and beverages. It’s often used before diagnostic radioactive iodine uptake (RAIU) tests and before radioactive iodine treatments. 

Example Meal Plan

The following are a few examples of low iodine meals to help you get started:

Low-iodine diets are necessary before these tests or treatments to “starve” the thyroid of iodine so the radioactive iodine (in capsule form) can get into the thyroid or thyroid cancer tissue more easily.

In addition to switching to non-iodized salt, those on a low-iodine diet should avoid foods such as bread with iodate dough conditioner, seafood, seaweed, processed foods, dairy, and more. When preparing to go on a low-iodine diet, it helps to prepare by stocking up on foods you can eat such as fresh vegetables and fruit.

A Word From Verywell

Following a new diet can feel overwhelming and frustrating. We’ve included some tips and example meal plans to help get you started. Contact your healthcare provider if you need extra guidance. They may be able refer you to a nutritionist or provide you with more direction.

Frequently Asked Questions

  • What foods are highest in iodine?
  • While not all breads have high amounts of iodine, those made with dough conditioner that includes potassium or calcium iodate have the highest amount of iodine. Other foods with high amounts include seaweed, seafood, oysters, iodized salt, dairy, eggs, and liver.
  • What happens if you don’t follow the low-iodine diet?
  • Not following a low-iodine diet before a radioactive uptake test may change the results of the thyroid scan. This will affect how your healthcare providers set up your treatment plan.If the radioactive iodine is a treatment, it may not be as effective.
  • How long do you have to be on a low iodine diet before an RAI scan?
  • Your healthcare providers will ask you to follow a low iodine diet seven to 14 days before a RAI scan or radioactive iodine treatment. Some people choose to start the diet a couple of days sooner to get used to it. You may also be asked to stay on the diet for one to two days after the scan or treatment.

While not all breads have high amounts of iodine, those made with dough conditioner that includes potassium or calcium iodate have the highest amount of iodine. Other foods with high amounts include seaweed, seafood, oysters, iodized salt, dairy, eggs, and liver.

Not following a low-iodine diet before a radioactive uptake test may change the results of the thyroid scan. This will affect how your healthcare providers set up your treatment plan.If the radioactive iodine is a treatment, it may not be as effective.

Your healthcare providers will ask you to follow a low iodine diet seven to 14 days before a RAI scan or radioactive iodine treatment. Some people choose to start the diet a couple of days sooner to get used to it. You may also be asked to stay on the diet for one to two days after the scan or treatment.