Iodine is a trace mineral that the body does not produce, making its intake through diet necessary for health. This mineral is the fundamental building block for thyroid hormones, which regulate metabolism, growth, and tissue repair. While iodine is usually promoted for health benefits, a specialized, short-term Low-Iodine Diet (LID) is sometimes required for medical purposes. The primary reason for following an LID is to prepare the body for radioactive iodine (RAI) therapy, a common treatment for certain thyroid cancers. By restricting iodine intake to less than 50 micrograms per day for one to two weeks, the thyroid cells more effectively absorb the therapeutic radioactive dose.
Foods to Strictly Limit or Avoid
The most concentrated sources of iodine are found in foods from the ocean, making all types of seafood a primary restriction. This includes all fish, shellfish, and especially sea vegetables like kelp, nori, kombu, and wakame, which contain extremely high amounts of iodine. Avoidance extends to fish oils, fish sauces, and any products listing seaweed derivatives such as carrageenan, agar-agar, or alginates.
Dairy products represent another major source of iodine. This iodine is not natural to the milk itself but results from modern farming practices, such as adding iodine to cow feed and using iodophor sanitizers. This leads to high iodine content in milk, cheese, yogurt, and butter. Whole eggs and egg yolks are also high in iodine due to supplementation in chicken feed, though egg whites are considered safe.
The third major restriction involves iodized salt, which is fortified to prevent deficiency. All commercial products made with iodized salt, such as most processed foods, canned soups, and restaurant meals, must be avoided. Many commercially baked goods are also restricted because they may contain iodate dough conditioners, dairy, or whole eggs.
A Comprehensive Guide to Low-Iodine Foods
The foundation of a low-iodine diet relies on using non-iodized salt, such as kosher salt or plain table salt that does not explicitly state “iodized” on the label. This swap allows for seasoning meals without the risk of adding the mineral. Fresh fruits and vegetables are excellent choices and can be consumed freely in their raw or frozen form, provided they are not mixed with high-iodine additives. Exceptions include maraschino cherries, which often contain Red Dye #3, and rhubarb.
Meats are allowed in limited amounts, usually up to six ounces per day of fresh, unprocessed cuts of beef, poultry, or pork. Since all meats contain a small amount of naturally occurring iodine, limiting the portion size helps keep the daily total below the 50 mcg target. Egg whites are safe and can be used as a protein source in place of whole eggs or yolks.
Many staple grains and cereals are safe, including rice, plain pasta, and oatmeal. Breads must be homemade or carefully selected from commercial brands verified to be made without iodized salt, dairy, or iodate dough conditioners. Fats and oils such as vegetable oils, olive oil, and unsalted nut butters are safe choices for cooking and flavoring. Beverages like water, coffee, tea, and fruit juices are acceptable, but dairy-based creamers or fortified milks must be avoided.
Identifying Hidden Sources of Dietary Iodine
Beyond the major food groups, iodine can be found in unexpected places, making label reading a necessity during the diet. Many multivitamins and nutritional supplements contain iodine, often as potassium iodide, and must be temporarily discontinued or replaced with an iodine-free version after consulting a physician. Certain food colorings, specifically the red food dye erythrosine (FD&C Red No. 3), contain iodine and are sometimes used in brightly colored candies and beverages.
Soy products like soy milk, tofu, and soy sauce are often limited. This restriction is not necessarily due to high iodine content, but because soy can interfere with the effectiveness of the RAI treatment. While soy oil and soy lecithin are considered safe, other soy proteins and fortified products should be avoided. Processed or canned foods often contain stabilizers, colorings, and a general lack of ingredient transparency, making most restaurant and fast-food meals risky and best avoided.