There is a common misconception that consuming goitrogens automatically leads to thyroid dysfunction or a goitre. However, no substantial evidence exists that validates this. Nonetheless, there are some populations who do need to be more aware of the goitrogens they consume and, with small tweaks, they can eat these foods with no ill effects on thyroid health.
So let’s clarify, what is a goitrogen?
A goitrogen is any substance that may interfere with iodine utilisation or thyroid hormone production. You may have heard of a goitre, an enlargement of the thyroid gland; it is one of the earliest signs of iodine deficiency.
The most well-known goitrogenic foods are those from the brassica family (broccoli, cabbage, cauliflower, mustard greens, Brussel sprouts, kale, kohlrabi, Chinese cabbage and rapeseed oil (better known as canola oil). Other lesser known goitrogens include: radishes and horseradishes, cassava root, soybeans, peanuts, pine nuts and millet.
In what conditions may goitrogens be a concern?
The population groups that should be most concerned with goitrogens are those who are iodine deficient, have subclinical hypothyroid, or have antibodies against thyroid proteins. The reason iodine is so important when you are discussing goitrogens is, iodine is a key regulator of thyroid gland function, directly modulating thyroid sensitivity to thyroid stimulating hormone (TSH).
Santos et al. undertook a review of all of the literature in 2011 and found that consumption of foods high in goitrogens was a contributing factor to the development of hypothyroidism and goitre if iodine deficiency was present.
It is also dependent on the amount of goitrogens consumed. It is estimated in commercial broccoli there is 10umol of goitrogen per 100g serving and this can be considered of minimal risk for thyroid health.
To counteract the possible interaction between low iodine/hypothyroidism and goitrogens, foods high in the trace minerals selenium and iodine need to be consumed in the diet.
Is soy milk detrimental to the thyroid?
A number of studies have raised concerns that soy milk can contribute to goitre. In one such study, infants were fed soy milk formula and goitre was observed; though notably this was usually reversed by changing to cows milk formula or supplementing with iodine.
Another study provided 30g of soybeans over a three month period and some participants experienced “hypo-metabolic symptoms and goitre”, with symptoms disappearing one month after the cessation of soybean ingestion.
Interestingly there was a retrospective epidemiological study undertaken on teenage children diagnosed with autoimmune thyroid disease (Hashimoto’s thyroiditis or Grave’s disease) and those children that had consumed soy formula as an infant had twice the prevalence of autoimmune disease when compared to their healthy siblings. Based on this, the message regarding soy safety is to monitor consumption if you have a family history of autoimmune conditions and if there is a possibility of iodine deficiency.
Which conditions could benefit from goitrogen-containing foods?
Foods containing goitrogens also contain other beneficial nutrients. For example, the compound sulforaphane is a powerful substance found in brassica vegetables that has been shown to exhibit anti-carcinogenic activity. So too does phenethyl and indolylic isothiocyanates, also found in brassica vegetables.
Menopausal women may also benefit from the flavonoids and soy phytoestrogens found in goitrogenic foods, as they have been shown to aid greatly in managing menopausal hot flashes and vaginal dryness.
How to limit exposure to foods containing goitrogens
- Goitrogens are inactivated through the cooking process, so limit the amount of goitrogen-containing foods eaten raw or lightly steam them.
- Iodine deficiency is exacerbated by selenium deficiency. So in addition to consuming iodine-rich foods, consuming foods high in selenium is good practice, such as brazil nuts, sardines and tuna.
- Include iodine-containing foods to protect against iodine deficiency. Eat seafood, shellfish, sea vegetables like kelp, dulse nori, wake and kombu, and iodised or sea salt.
- Switch or alternate soy with other forms of vegetable protein such as pea or brown rice protein.
- Substitute soy milk with other milks like almond, coconut or oat.
- Rotate goitrogenic vegetables with other green leafy vegetables including baby spinach, beetroot leaves, celery leaves as well as different types of lettuce and rocket.
- Eat vegetables exhibiting all of the colours of the rainbow such as carrots, apples, blueberries and beetroots.
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