Post by Emily White
Who here is scared of kale? For anyone who has Facebook you no doubt would have recently seen numerous articles announcing the ‘dark side’ of kale- I’m not even joking here- one was literally titled ‘the dark side of kale’ as if to say it sneaks out of your fridge at night while you sleep and murders your family….
If nutrition wasn’t confusing enough, kale has literally gone from a ‘super-food’ to a ‘health warning’ overnight. So is there any truth to these claims or is it just another media storm in a teacup?
So first lets look at ‘why’ kale has suddenly become the devil. Kale contains glucosinolates which when metabolized may produce a compound called goitrin which has been found to interfere with the synthesis of thyroid hormones by competing with iodine uptake into the thyroid gland (1). I’m not entirely sure why it is just kale that has been pushed under the bus as this applies to all cruciferous vegetables. That means this is the case for your beloved (or possibly not so beloved) cauliflower, broccoli, Brussels sprouts and cabbage (1).
So after finding all of this out I set out to find evidence of the detrimental effects of cruciferous vegetables. There has been one case report to date, of an 88-year-old woman developing severe hypothyroidism and coma following the consumption of cruciferous vegetables. The catch? She was consuming an estimated 1.0 to1.5kg/day of raw bok choy for several months (2). That is the equivalent of about 15 cups of kale per day! So as you can imagine the amount of kale you’d have to eat would be pretty extreme to bring on any serious health problems. Research is suggesting that unless there is a coexisting thyroid issue, cruciferous vegetables are generally harmless (3).
One study in particular suggested that increased consumption of these vegetables does not appear to increase your risk of hypothyroidism unless it is accompanied by iodine deficiency (4). Another study looked at the consumption of Brussels sprouts and thyroid function and found that consumption of 150g/day of cooked Brussels sprouts for four weeks had no adverse effects on thyroid function (3).
It is also important to note, that the goitrogenic properties of kale, or any other cruciferous vegetable are greatly reduced when cooked- so if you are really concerned, cooking these vegetables can alleviate any stress (4). Also ensuring you are getting enough iodine (which is extremely important for normal functioning anyway) can be of benefit.
Therefore I wouldn’t go placing a life ban on kale. If you do not have an iodine deficiency or thyroid issues, the intake of potential goitrogens should not cause a problem. It could also be worth noting that maybe, just maybe, we shouldn’t be taking all the things that pop up on our Facebook news feeds as gospel anyway. Kale comes with a vast range of health benefits and therefore in 99% of cases you are going to be better off consuming it, then not.
1. Trumbo, P., Yates, A. A., Schlicker, S., & Poos, M. Dietary Reference Intakes. Journal of the American Dietetic Association, 101(3), 294-301. doi: 10.1016/S0002-8223(01)00078-5
2. Chu, M., & Seltzer, T. F. (2010). Myxedema coma induced by ingestion of raw bok choy. N Engl J Med, 362(20), 1945-1946. doi: 10.1056/NEJMc0911005
3. McMillan, M., Spinks, E. A., & Fenwick, G. R. (1986). Preliminary observations on the effect of dietary brussels sprouts on thyroid function. Hum Toxicol, 5(1), 15-19.
4. Truong, T., Baron-Dubourdieu, D., Rougier, Y., & Guenel, P. (2010). Role of dietary iodine and cruciferous vegetables in thyroid cancer: a countrywide case-control study in New Caledonia. Cancer Causes Control, 21(8), 1183-1192. doi: 10.1007/s10552-010-9545-2