Broccoli and other cruciferous vegetables like cauliflower, kale and cabbage are not inherently “bad” for the thyroid – but they may need to be limited – or at least thoroughly cooked – by people with goiter or hypothyroidism. Broccoli is actually full of beneficial substances which have been shown to reduce the risk of certain cancers like colorectal, lung, prostate and breast cancers. If you have normal thyroid function, the goitrogenic substances found in broccoli are probably outweighed by all the other health benefits found in cruciferous vegetables.
Thiocyanates and Thyroid Function
A class of compounds in broccoli that have been isolated as goitrogenic – that is a substance that contributes to the development of a goiter in at-risk individuals – are called thiocyanates. Isothiocyanates are made from phytonutrients known as glucosinolates, which are found in abundance in cruciferous vegetables like broccoli. These substances seem to interfere with iodine absorption, particularly where iodine is limited in the diet, and have been linked to the formation of goiters in low-iodine regions like parts of Africa that rely heavily on foods containing high levels of thiocyanates – in this case the cassava root.
Nutrient Deficiencies and Goitrogens
A deficiency in both iodine and selenium may be related to the anti-thyroid action of thiocyanates, according to the George Mateljan Foundation website. For hypothyroid sufferers whose thyroid disorder is not caused by a nutrient deficiency, limiting broccoli and other goitrogenic foods may not be necessary, according to thyroid specialist Dr. Alan Christianson – up to 95 percent of hypothyroidism in the U.S. is not caused by an iodine deficiency, but rather by an autoimmune reaction. In fact, acupuncturist and natural health expert Chris Kresser claims that excess iodine might be implicated in the higher levels of autoimmune thyroid disease in the industrialized world, and in that case the slowing of iodine absorption caused by thiocyanates might be beneficial for those suffering from autoimmune hypothyroidism.
The Effects of Cooking on Goitrogenic Compounds
Experts agree that cooking eliminates at least some of the goitrogenic substances in broccoli – but just how long to cook cruciferous veggies remains a bit unclear. Dr. Andrew Weil proposes that even a light steaming will deactivate most of the glucosinolates in broccoli, however nutrition expert Chris Masterjohn proposes that to remove 90 percent of the goitrogens, cruciferous vegetables need to be boiled for 30 minutes. According to Masterjohn, fermenting broccoli and other cruciferous vegetables actually enhances their goitrogenic actions.
If you don't have any underlying thyroid conditions, it is probably safe – and even recommended – to eat plenty of broccoli. You may want to avoid eating huge quantities of raw broccoli if you have a family history of thyroid trouble, or are concerned that you might develop hypothyroidism. For those already suffering from thyroid disease, limiting broccoli and avoiding it raw are probably wise choices since the evidence still isn't entirely in with regards to how goitrogens affect different types of thyroid disease. A diet that has a lot of diversity can provide you with many of the health benefits found in different foods without the risk associated with excessive consumption of just one type.
Articles For Your Diet
- The World's Healthiest Foods: An Up-to-Date Look at Goitrogenic Substances in Food
- Asian Pacific Journal of Cancer Prevention: Cruciferous Vegetables: Dietary Phytochemicals for Cancer Prevention
- Healthful Elements: Goitrogenic Foods: Thyroid Busters or Thyroid Boosters?
- Chris Kresser, L. Ac: Iodine for Hypothyroidism: Like Gasoline on a Fire?
- Andrew Weil, M.D.: Is Broccoli Bad for the Thyroid?
- The Weston A. Price Foundation: Bearers of the Cross: Crucifers in the Context of Traditional Diets and Modern Science
- BananaStock/BananaStock/Getty Images