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Q: Can I eat cruciferous vegetables (e.g. cabbage, kale, cauliflower, broccoli) if I've had my thyroid removed OR are taking thyroxin tablets?
A: It is not necessary to eliminate cruciferous vegetables from the diet in this case but rather, to limit intake so that it falls into a reasonable range. In fact, they are incredibly nutritious for all sorts of reasons and offer a powerful insurance against a wide range of cancers, incidentally also protecting against thyroid cancer.
A number of studies have been done researching the link between cruciferous vegetables (in particular their goitre-causing phytochemicals) and hypothyroidism (insufficient thyroid hormone) raising many questions as to the health safety of eating cruciferous vegetables such as kale, broccoli, cabbage, cauliflower, turnip and Brussels sprouts.
A study in 1983 showed that very high intakes of cruciferous vegetables caused hypothyroidism in animals. However, the effects of cruciferous vegetable consumption did not appear to increase the risk of hypothyroidism UNLESS accompanied by iodine deficiency.
In other words, at moderate consumption levels of cruciferous vegetables, the effect of their goitrogenic properties can be overcome by increasing your intake of iodine.
Nutrition from cruciferous
Cruciferous or Brassica vegetables are, in fact, incredibly nutritious (some of them are 'super foods' packed with Vitamin C and fibre!) and offer a powerful insurance against a wide range of cancers, incidentally also protecting against thyroid cancer.
- If you've had your thyroid removed you don't need to be particularly concerned about cruciferous vegetables and their ability to interfere with your thyroid function. They can't. Once the thyroid tissue is destroyed, it will not regrow.
- If you have a low functioning thyroid and are on thyroxin tablets, the goal is not to eliminate goitrogenic foods from the diet but to limit intake so that it falls into a reasonable range. There have been no clear-cut studies on what a reasonable serve looks like - you'll get different versions of what and how much to eat when you ask different sources.
My examples of 'average' and safe serves of cruciferous vegetables are:
- Cabbage: 1 cup shredded raw or ½ cup cooked
- Broccoli: ½ cup florets (about 4-5)
- Cauliflower: ½ cup florets (about 4-5)
- Brussels sprouts: 4-5
Vary the cruciferous vegetables you eat as they may have one or more, and varying quantities, of the known goitrogenic phytochemicals. And remember, the most effective way to ensure safe consumption of cruciferous vegetables is to check your thyroid and iodine levels and if necessary boost your iodine intake.
In the absence of thyroid problems, there is no research evidence to suggest that cruciferous vegetables will negatively impact your health.
IODINE - the basics
Iodine is a mineral required by the body in small amounts. It is not stored in the body to any great extent so regular consumption of foods containing iodine is essential for good health.
Iodine is found in:
- dairy products - as a contaminant from iodophores used as sanitising compounds in dairies but these have been largely replaced by chlorine-based sanitisers
- seafood (crab, prawns, lobster, mussels, oysters)
- seaweeds such as nori and kelp
- some vegetables - but depends on the soil they're grown in
- iodised salt
Note: almost all bread in Australia is now required to be made using iodised salt to prevent mild iodine deficiency.