Goitrogenic Foods and Thyroid Health

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Goitrogenic Foods and Thyroid Health

on April 19, 2018

by Chris Kresser

Warnings about goitrogenic foods are popping up on alternative and conventional healthcare sites alike. The truth is, goitrogens can be a problem, especially for patients with thyroid problems. Read on to learn what foods are goitrogenic, how food can be prepared to limit them, and which patients should be extra concerned about goitrogens.


The thyroid controls metabolism

The small, butterfly-shaped thyroid gland has big responsibilities. The thyroid and its hormones control metabolism throughout the body, affecting the brain, GI tract, cardiovascular system, lipid and cholesterol metabolism, hormone synthesis, gallbladder and liver function, and more.

Unfortunately, 20 million Americans suffer from some form of thyroid disease, and 60 percent of those who have it may not even be aware. One in eight women will develop a thyroid disorder in her lifetime. If something disrupts thyroid function, the health consequences can be widespread.

Goitrogenic substances interfere with iodine uptake in the thyroid

The term “goitrogenic” means something that causes “goiter,” or swelling of the thyroid gland. Goitrogens accomplish this by interfering with iodine uptake in the thyroid gland. When not enough iodine is available, the thyroid cannot produce sufficient levels of thyroid hormones T4 and T3. The hypothalamus senses low T4 and releases TSH-releasing hormone, which triggers the pituitary gland to produce TSH. The thyroid gland responds to TSH by making more hormones. If it can’t keep up with demand, it grows bigger trying.

Goitrogens, found in many vegetables, can be problematic for patients with thyroid disorders.

Goitrins, thiocyanates, and nitriles are all goitrogenic chemicals derived from natural plant pesticides called glucosinolates. During digestion, an enzyme breaks down glucosinolates into both goitrogenic and non-goitrogenic byproducts (1).

Foods that have been identified as goitrogenic include cruciferous vegetables such as bok choy, broccoli, brussels sprouts, cabbage, canola, cauliflower, Chinese cabbage, coy sum, collard greens, horseradish, kai-lan, kale, kohlrabi, mizuna, mustard greens, radishes, rapeseed, rapini, rutabagas, and turnips. The Rosaceae family of fruits, which includes almonds, apricots, cherries, peaches, pears, plums, raspberries, and strawberries, is also goitrogenic. Other examples are bamboo shoots, millet, soy, spinach, sweet potato, tapioca, and yuca (cassava or manioc).

Many chemicals from the environment and medications are also classified as goitrogenic:

  • Amiodarone (medication for irregular heart beat)
  • Antibiotics
  • Bromides (from pesticides, plastic, brominated vegetable oils, medications)
  • Dioxins (toxic industrial byproducts)
  • Heavy metals
  • NSAIDs
  • Lithium and benzodiazepines (depression and anxiety drugs)
  • Oxazolidines (from paint)
  • Perchlorates (from jet fuel, water)
  • Pesticides
  • Thiocyanate (in cigarettes)

At relatively low concentrations, goitrogens decrease the uptake of iodine by the thyroid gland. This effect can often be offset by supplementing with iodine. However, exposure to large amounts of goitrogens impairs the incorporation of iodine into thyroid hormone itself, which means that the thyroid gland can’t properly utilize the iodine. In this case, no amount of supplemental iodine would be able to overcome a large intake of goitrogenic substances.

Kale and broccoli: health foods or thyroid toxins?

Goitrogens are not an outright death sentence for kale and broccoli. Fruit and vegetable consumption in general lowers the risk of chronic diseases (2). Before you stop recommending antioxidant-rich fruits and vegetables to your patients, keep reading. The goitrogen content of foods varies widely and can be modified.

Crucifers are the biggest goitrogenic offenders, with certain varieties of kale, collard greens, and brussels sprouts at the top of the list. Others have significantly lower goitrogen levels. For example, the progoitrin (one of the harmful downstream products of glucosinolates) content per dry weight of Russian kale is approximately 150 times higher than that of Chinese cabbage (1).

Fortunately, cooking lowers the goitrogenic content of foods. Steaming crucifers until fully cooked reduces goitrogens by two-thirds. Boiling crucifers for 30 minutes destroys 90 percent of the goitrogens by stimulating the production of myrosinase, an enzyme that helps deactivate goitrogenic glucosinolates (3).

On the flip side, when green vegetables are boiled and the water is discarded, some beneficial nutrients are lost as well. About 45 percent of the vitamin C, 20 percent of the thiamin, and 40 percent of the folate are lost (4). Minerals (calcium, iron, etc.), vitamin B12, vitamin A, and others are very well retained. Steaming versus boiling will retain more nutrients. Although some nutrients leach out, cooking goitrogenic foods is generally beneficial.

In contrast to cooking, fermenting increases the goitrogen content of cabbage, but it simultaneously decreases the level of nitriles (5). Because nitriles are more harmful than goitrogens, the overall effect of fermentation is probably positive.

In a given week, if a patient is enjoying a couple of sides of steamed broccoli, a few servings of sauerkraut, and several small salads containing spinach and kale, that shouldn’t be a problem. On the other hand, if a patient is downing green smoothies every day, each with two or more cups of raw kale or spinach, then I would be worried about how that’s affecting thyroid function.

Bottom line: encourage your patients to steam or boil goitrogenic foods and not to consume them in excess.

Patients who are susceptible to goitrogenic foods

Certain groups of patients need to take special considerations when it comes to goitrogenic foods:

Patients at risk for iodine deficiency. As stated earlier, goitrogens reduce the uptake of iodine in the thyroid. If someone is already iodine-deficient, then goitrogens are more likely to cause issues. Despite iodized salt supplementation programs, iodine deficiency is on the rise. In Europe, it’s estimated that up to 44 percent of the population maybe be iodine-deficient (6).

The best food sources of iodine come from the sea: seaweeds, cod, shrimp, and tuna. Eggs and iodized salt are also options. Have your patients start with lower-iodine-containing foods and work their way up to higher levels. Simultaneously, ensure proper selenium intake. Selenium is best obtained from foods such as Brazil nuts, cremini mushrooms, cod, shrimp, tuna, halibut, salmon, scallops, chicken, eggs, shiitake mushrooms, lamb, and turkey.

Patients with thyroid problems. For patients already experiencing thyroid problems, especially hypothyroidism, goitrogens will exacerbate the condition (1). These patients should be limiting their cruciferous vegetables to one cooked serving per day. And take it easy on the green smoothies!

If you suspect a patient has thyroid issues, make sure you run a full thyroid blood work panel, which should include the standard TSH and T4, but also T3, free T3, free T4, and thyroid antibodies.

Pregnant and nursing women. Pregnant and nursing women require 50 percent more iodine than the average adult, making them extra susceptible to iodine deficiency (789). Goitrogens can inhibit the transfer of iodine into a mother’s breast milk. In a study of Boston mothers, 47 percent of breast milk samples did not have sufficient levels of iodine (10). I recommend only three to five servings per week of cooked cruciferous vegetables and other highly goitrogenic foods for these patients.

Further dietary considerations for thyroid health

Patients with thyroid disorders may also want to consider other dietary choices.

Oxalates. Oxalates protect plants from being eaten by critters and are found in most plants, nuts, and seeds. Spinach, okra, sweet potato, elderberry, figs, leeks, buckwheat, celery, other leafy greens, and dandelions are some sources. For frame of reference, ingesting 250 mg of oxalates is considered high, and one cup of raw spinach contains a whopping 656 mg (11).

Oxalic acid binds minerals like calcium and potassium, making them insoluble and less bioavailable (12). Oxalate salts increase the risk of kidney stones, especially in patients with gut dysbiosis. Gut bacteria are responsible for breaking down oxalates, but when the microbiota are compromised, oxalates can enter the blood, turn into crystals, and get stored in tissues like the kidney. In one study, 65 percent of kidney stones contained calcium oxalate (13). Unfortunately, cooking doesn’t decrease the oxalate content much.

Foods that may trigger an immune response. For patients with an autoimmune thyroid disorder, eggs, nightshades, and dairy products are common offenders.

Industrial seed oils. Chronic inflammation can worsen thyroid disorders. The high content of omega-6 fatty acids in industrial seed oils drives inflammation.

Very-low-carb or low-protein diets. Carbs and proteins both promote the release of insulin, which is required to convert T4 to T3. Have your patients aim their macros to at least 20 percent carbs and 10 percent protein. The increasingly popular keto diet may not be appropriate.

Other strategies to improve thyroid function

I deal with thyroid disorders often in my practice, and they can be very complex conditions. For more information, check out my articles about the thyroid’s connection with cardiovascular disease, the gut microbiome, blood sugar, and more. Beyond limiting goitrogenic foods, other strategies I recommend to improve thyroid function include the following:

Now I’d like to hear from you. Do you educate patients with thyroid disorders about goitrogenic foods? What other strategies do you recommend for improving thyroid health? Let us know in the comments below!

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