How many unreferenced blogs have you come across warning you that kale, and other vegetables from the Brassica family, are, in fact, dangerous and interfere with thyroid functions and its hormones.
On the other hand, pro-organic and nutritional experts claims that eating brassicas (once called green leafy vegetables, or cruciferous), for they are topping the list of nutrient-dense foods, ranked according to how many nutrients a specific food supplies compared to its calorie content, must be eaten at every meal.
Brassicas, including kale, are packed with key minerals, especially magnesium, vitamins, essential fatty acids, enzymes, compounds that have antioxidant properties and other that are useful in detoxification, and much much more.
How could kale be labelled as dangerous?
It will always surprise me how some studies are conducted to create new headlines, and how many people will jump on the wagon, spreading what they have “uncovered” without thorough research of their own.
The farce on cholesterol and fat is the perfect example how a lie can enter the government association circles and make it to the top of their agendas.
It is obvious that giving fat to a rabbit, because everyone knows a rabbit is a carnivore, right? And that, as a result cholesterol in the blood of the rabbit rises and this leads to cardiovascular risk.
But what has this to do with Kale?
Goitrogens were identified nearly a century ago (1928).
It was uncovered that goitrogens “goitrogens had an anti-carcinogenic effect. Despite the high spontaneous tumor incidence in A strain mice, during goitrogenic treatment such mice had no spontaneous tumors, even in old age.” (Gorbman, A. 1947. pp. 756)
This is in a way quite old news, and yet, brassicas only received widespread attention once the ANDI score was invented in the late 90s and taken on board by the likes of Wholefoods years later in the hope to help people make better choice when shopping for food.
Kale has then become the queen of plants, scoring 1,000 on the ANDI scale, the maximum score possible.
When attention is given to something in particular there will always be the doubters and others who just want the attention to go away.
That we want it or not, any plant or herb exerts a therapeutic (medicinal) effect on the body. Like a medicine, some people can react to food or be susceptible to some of their compounds.
It has been long known that thyroid function is disturbed during pregnancy and that brassicas may exert further goitrogenic effect on the thyroid, especially, if consumed in larger quantity.
What are goitrogens?
According to Thyroid UK: “Goitrogenic foods can act like an antithyroid drug in disabling the thyroid function. They prevent the thyroid from using available iodine. It is made worse if you use a lot of salt because that causes the thyroid to swell.
“Cruciferous vegetables contain thioglucosides that are metabolized to thiocyanates. These compounds inhibit iodine transport and the incorporation of iodide into thyroglobulin, thus increasing TSH secretion and thyroid cells proliferation. In animal experiments, it has been found that these substances induce thyroid carcinomas. Another group of potent goitrogens are contained in food such as cassava or sweet potatoes, with high content of cyanogenic glycosides. In epidemiological studies, no clear association between thyroid cancer and cruciferous vegetables or other food items containing goitrogens has been demonstrated.” (Truong, T. et al. 2010. p. 1184)
Goitrogens are compounds that interfere with the normal function of the thyroid gland, disturbing hormone production, and it closely linked to iodine (excess or deficiency).
There are four types of goitrogens:
Goitrins, nitriles and thiocyanates are the result of chemical reactions when plants are damaged, such as when they are sliced or chewed, creating glucosinates, a plant self-defence mechanism (pesticide). Gucosinates are broken down in our body during digestion into goitrogenic and non-goitrogenic compounds.
Flavonoids are naturally present in a wide variety of foods and have antioxidant properties, but some of them can be converted into goitrogenic compounds by our gut bacteria
The danger of goitrogens?
There is only one reported case of thyroid dysfunction because of brassica intake. The person was, in fact, consuming exceptionally excessive doses every single day.
You may need to worry about goitrogens if you suspect, or were diagnosed with thyroid dysfunction, if you are pregnant or nursing.
And this is from this incident that today kale is Mankiller!
The other great danger is that many people are not aware that they have thyroid problems, because symptoms are so broad (stress, fatigue, poor memory and concentration, weight gain, etc.)
Which food have the highest content of goitrogens?
A surprising variety of foods contain goitrogens, including vegetables, fruits, starchy plants and soy-based foods.
How problems start?
For people with thyroid problems, coupled with iodine deficiency, high intake of goitrogens can disturb thyroid function even further by:
Thyroid dysfunction can lead to symptoms linked to energy and metabolism: body temperature, heart rate, protein production, use of fat and carbohydrates for energy, with an increased risk for weight gain, obesity, heart disease, metabolic syndrome, liver and gallbladder dysfunction, and cognitive decline.
The body’s response is to release more TSH. The thyroid gland responds to TSH by making more hormones and, if it cannot keep up, compensates by growing more cells, leading to an enlargement known as a goitre.
Certain varieties of kale are the biggest goitrogenic offenders, together with collards and Brussels sprouts, so there is reason to minimise their intake if you suffer from thyroid problems, at risk of iodine deficiency, pregnant or nursing.
It is also important to note that thyroid dysfunction occurs because of gut and widespread inflammation, often due to food sensitivities, sugar-rich diet, regular alcohol intake, foods that may induce an immune response, and an omega-6-rich diet (vegetable oils and mass-produced red meats). A very-low carbohydrate and a low-protein diet can interfere with thyroid hormone because it requires insulin to covert T4 to T3 (active thyroid hormone).
Many environmental chemicals and medications are also classified as goitrogenic:
Oxalates can also present another problem for people with thyroid disorders. Oxalates are compounds natural found in plants and are able to bind to minerals preventing them to be assimilated by the body.
Because Thyroid dysfunction starts in the gut (dysbiosis, gut inflammation, food sensitivities, etc.), it often reveals an unbalanced gut microflora (dysbiosis). Oxalates are broken down by gut bacteria, but when gut microflora is compromised, oxalates can also enter the bloodstream and turn into crystals ending in kidney tissue (kidney stones).
So, is kale a silent killer?
The answer is not really.
Goitrogens are not an outright death sentence. When cooked and consumed in moderation, Kale, and other members of the brassica family, should be safe for everyone — even those with thyroid problems
If you follow a healthy diet, eat little processed food and a wide range of colourful fruits and vegetables, exercise as often as you can, there will be little chance to have issues with your thyroid, especially if you avoid foods susceptible to generate inflammation, such as alcohol, sugar, and food known to disturb your gut integrity and bacterial microflora (gluten, dairy, oxalates and phytates).
Cooking lowers the goitrogenic content of food. Often, I recommended to lightly steam green leafy vegetables to preserve all the nutrients, but you may boil them further if you have thyroid impairment, and limit your intake to one serving per day if you have hypothyroidism. And of course, it is all about moderation. Anything in excess is bound to create issues.
AVOID drinking many green juices made with raw cruciferous and, especially, spinach (very high in oxalates), and AVOID eating brassicas raw.
"Fermenting increases the goitrogen content of cabbage, but it simultaneously decreases the level of nitriles. Because nitriles are more harmful than goitrogens, the overall effect of fermentation is probably positive". Explains Kris Kresser*
Make sure you ingest enough iodine every day to prevent deficiency and multiply the goitrogenic effect of kale and other vegetables from the brassica family.
Other effective Strategies to improve Thyroid function
The most important factor when it comes to thyroid dysfunction is systemic inflammation. Usually, this is the result of gut inflammation, bad oral care, food intolerances, high intake of sugar and alcohol, chronic stress and a disproportionate stress response, anxiety and depression.
Mastering blood sugar in these case is primordial.
Heal the gut. Remember that gut bacteria assist to convert T4 to T3.
Check you Vitamin D level and maximise safe sun exposure. Vitamin D is involved in immune function and autoimmunity. Hypothyroidism is often the result of autoimmunity, a cross reaction with the molecule of gluten in particular.
Exclusively opt for Organic or Biodynamic food and avoid highly-processed and refined foods as much as possible. This will help you reduce your intake of toxins.
Make sure you consume enough Selenium-rich foods.
Eat a varied, balance diet.
The last word
(Knusden, N. et al. 2002. p. 879)
"The occurrence of thyroid diseases is determined by interplay between genetic and environmental factors. The major environmental factor that determines goiter prevalence is iodine status, but other environmental factors influencing entire populations have been identified such as goitrogens in food and drinking water. Less focus has been on individual environmental factors and the interplay between factors. The goiter prevalence is higher in certain groups in the population. The variation in goiter prevalence between the genders is well known with a higher occurrence among women. The association with age is probably dependent on iodine status, because it seems that the zenith of goiter prevalence appears earlier in life the more severe iodine deficiency the population is exposed to. The association with individual risk factors has been investigated in some studies, especially the association with tobacco smoking. In iodine-deficient areas, a strong association between tobacco smoking and goiter prevalence is found, whereas the association is less pronounced in iodine-replete areas. This was predictable from experimental studies showing thiocyanate to be the mediator of the goitrogenic effect of tobacco smoke acting as a competitive inhibitor of iodine uptake. The association with alcohol intake has only been investigated in few studies, but a low occurrence of goiter among alcohol consumers has been found. The mechanism of this association is not known. Increased goiter prevalence during pregnancy has been reported, and recently a long-term goitrogenic effect of pregnancies has also been shown. As demonstrated for tobacco smoking, this association is dependent on iodine status, because the association has only been found in areas with a suboptimal iodine intake. This indicates pregnancy-induced goiter to be the result of exacerbation of existing iodine deficiency. Recently, the use of oral contraceptives has been shown to be associated with a markedly reduced prevalence of goiter, although experimental studies have previously shown proliferative effects of estrogens on thyrocytes. Some implications for prevention of thyroid disease could be suggested. Discussion of smoking habits should be included in a consultation for goiter with a motivation to quit smoking. Iodine deficiency has particularly strong goitrogenic effects during pregnancy and for the sake of the mother as well as the fetus, sufficient iodine supply should be ensured to all pregnant women. The difference in age maximum in goiter prevalence suggests that monitoring of iodine deficiency disorders should ideally include a spectrum of age groups."
(click on this link for help)
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Registered Naturopath, Nutritional Therapist, Iridologist, Lecturer, NLP practitioner and Personal Performance Coach.