Does broccoli suppress your thyroid?

Thyroids are big news right now, and low thyroid activity seems to be an increasingly common affliction, leading to a wide range of signs from difficulty in losing weight through to hair loss. I have written this article to clear up some misinformation that you might have heard, which relates to some authors telling you that broccoli is bad for you and that it’s likely to be making you fat. Yes, seriously! This seems to have sent a certain amount of panic through those health-conscious people who enjoy their broccoli, and better still, broccoli sprouts, for their health-giving properties.
This article has been written to address the concern that broccoli and other cruciferous vegetables are inhibiting your thyroid function, and therefore potentially making you fat. I know, it sounds mad doesn’t it?
So, where has this information come from, and is it true? You can probably guess that I am going to tell you that this suggestion is a load of nonsense, but before dismissing it out of hand, let’s see where it all started…
The concerns surround a group of compounds called the glucosinolates, which are present in all cruciferous vegetables. When glucosinolates are broken down in the intestines, some interesting compounds are formed which have significant health benefits (see below), ranging from reduction in oxidative stress to inhibition of cancer, and  the ability to
repair DNA. However, they also have effects on the thyroid glands.
According to an article published in European Food Research and Technology (1), sprouted broccoli contains lower levels of glucosinolates than the seed, so this could be good news and adds weight to the recommendations to enjoy sprouted seeds for their health benefits.
The hydrolysis (digestion) of some glucosinolates found in cruciferous vegetables (e.g., progoitrin) can lead to a compound known as goitrin, which has been found to interfere with the production of thyroid hormone. The hydrolysis of another class of glucosinolates, known as indole glucosinolates, results in the release of thiocyanate ions, which can
compete with iodine for uptake by the thyroid gland. Increased exposure to thiocyanate ions from cruciferous vegetable consumption does not appear to increase the risk of an underactive thyroid, unless you also have iodine deficiency.
However, this seems to be how some of the concerns have come about, with some authors making a massive, and somewhat unjustified extrapolation that because the digestion of broccoli produces these compounds, it must therefore suppress thyroid function. The good news is that, despite several decades of speculation, no evidence exists that links the consumption of foods high in glucosinolates to the suppression of the thyroid glands to create a genuine thyroid underactivity (2).
Iodine deficiency has been flagged up by some experts to be an increasing problem, so this of course needs to be addressed. Many foods have a good iodine content, but perhaps the best-known one is seaweed. That is one of the reasons why I recommend adding sea vegetables to your salads. They are a fantastic source of all minerals, not just iodine.
Glucosinolates also have many beneficial effects. They have been shown to induce the activity of the phase II detoxification enzymes and inhibit phase I (activating) enzymes, exerting an anticancer effect (2, 3, 4). They have also been shown to provide protection from oxidative stress through elimination of free radicals (3, 5).   It is thought that this activity may be behind the observed link between brassica vegetable intake and cancer-protective effects (6, 7).
So, armed with this information, what do I suggest that you need to do? Firstly, keep on eating your broccoli and other cruciferous vegetables (kale, sprouts, cabbages, bok choi etc) unless you have been diagnosed with an underactive thyroid (hypothyroidism). Secondly, eat some seaweed. Thirdly, remember that it is also the quantity of brassicas that you consume which has an effect. To get glucosinolate toxicity, you would have to be eating several kilograms of produce per day – pretty unlikely for the average person – even a raw fooder like me.
Don’t be put off by the fact that you may be advised not to eat raw broccoli. Whilst boiling your broccoli prior to eating it will destroy the glucosinolates, remember that they are good for you in moderate quantities. Steaming your broccoli has no effect on glucosinolate content – it’s the boiling water that destroys the compounds.
Remember that there are some foods that genuinely do suppress your thyroid, and one of those is processed soya, which I do not recommend that you eat. Ultimately, the epidemic of obesity which developed countries face is not because of a sudden increase in the global consumption of broccoli. It is largely as a result of the increased consumption of sugar, processed junk, and reduction in activity levels. So you can keep eating your greens!
You’ll find more on thyroid health and the other nutrients you need for happy thyroid glands in my book The Whole Body Solution.
You can get lots of information on the importance of minerals in my new, studio-recorded CD of the same name.
You’ll find out more about reversing damaging free radicals in my new, studio-recorded CD Oxidative Stress and the Link Between Diet and Health.
Want to know more about the damaging effects of sugar? Try my new, studio-recorded CD The Dangers of Excess Sugar Consumption.
And finally, if you want to know what you should be doing and eating to achieve optimal health, why not join me on a fantastic weekend retreat? Go here for all the details.
1. Michael Rychlik, Sieghard T. Adam. Glucosinolate and folate content in sprouted broccoli seeds. European Food Research and Technology, March 2008.
2. Cartea ME, Velasco P. (2008) Glucosinolates in Brassica foods: Bioavailability in food and significance for human health. Phytochemistry Reviews; 7(2): 213-229.
3. Jeffery EH, Araya M. (2009) Physiological effects of broccoli consumption. Phytochemistry Reviews; 8(1): 283-298.
4. Johnson IT. (2002) Glucosinolates in the human diet. Bioavailability and implications for health. Phytochemistry Reviews; 1(2): 183-188.
5. Traka M, Mithen R. (2009) Glucosinolates, isothiocyanates and human health. Phytochemistry Reviews; 8(1): 269-282.
6. London SJ, Yuan J-M, Chung F-L, Gao Y-T, Coetzee GA, Ross RK, Yu MC. (2000) Isothiocyanates, glutathione S-transferase M1 and T1 polymorphisms, and lung cancer risk: a prospective study of men in Shanghai, China. Lancet; 356(9231): 724729.
7. Verhoeven DTH, Goldbohm RA, Van Poppel G, Verhagen H, Van Den Brandt PA. (1996) Epidemiological studies on Brassica vegetables and cancer risk. Cancer Epidemiology Biomarkers and Prevention; 5(9): 733-748.

About Max Tuck

Hippocrates Health Educator. Long term living foods vegan. Athlete, lecturer, author of four books (with the 5th coming soon) and firm advocate of healthy living.
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