The following sentence is usually paraded to anybody who questions whether brassica vegetables (BV's) can cause an underactive thyroid:
"The scientific consensus is that cruciferous vegetables could only be detrimental to thyroid function in cases of iodine deficiency or insufficient iodine intake.”
Ask yourself this: if BV's can only be detrimental to thyroid function in cases of iodine deficiency, why should BV's not be detrimental in cases of no iodine deficiency? If BV's have no detrimental effect on the thyroid, why should BV's somehow only be detrimental in the face of iodine deficiency?
Goitrogenic compounds have no effect on levels on iodine in the bloodstream (they don't neutralize or replace iodine). But goitrogens do affect the thyroid itself by making the thyroid less capable of accepting and using iodine. Goitrogens do this regardless of the level of iodine in the diet or in the blood.
Therefore to say that the goitrogens in brassica vegetables "could only be detrimental to thyroid function in cases of iodine deficiency" cannot be correct.
Some doctors say that goitrogens in brassica vegetables "compete with iodine for thyroidal update" thus implying that if you are not short of dietary iodine, such competition does not matter. In fact, goitrogens in brassica vegetables do not compete with iodine; this is farcical because the thyroid cannot use goitrogens in place of iodine, so there is no 'competition'.
To clarify this important point further, imagine that you put water into a car's fuel-tank instead of fuel: the car won't run! Water does not compete with fuel. It's the same with the thyroid. The thyroid works with iodine, not goitrogens. The goitrogens in BV's do not compete with iodine. Putting water into a fuel tank stops the car working. Similarly, goitrogens prevent the thyroid from working properly. If you add fuel to a car after putting water into the fuel tank, the car still won't work properly. If you add iodine to your diet while still consuming goitrogens in BV's, the thyroid still won't work properly.
Here is a real-life example to illustrate the point that iodine supplementation makes no difference in the face of a diet high in goitrogens.
Pearl millet is known to be high in goitrogenic glucosinolates, on a par with, say, broccoli. In the Sudan it was observed that "where pearl millet was the only staple, the incidence of goitre was higher than in urban regions where other food-grains such as sorghum were consumed. Consumption of pearl millet is considered one of the factors responsible for the high incidence of goitre in rural populations. A positive correlation observed between the incidence of goitre and per caput production of pearl millet in six African countries supports this viewpoint. Furthermore, [it was] observed that rats fed pearl millet diets developed abnormal thyroid hormone patterns with hyperplasia while animals fed sorghum were unaffected. Feeding trials in rats showed that the goitrogen in pearl millet inhibited [thyroid] hormone. Iodine supplementation did not alleviate the goitrogenic effect of pearl millet".
Source: FAO United Nations, Sorghum and millets in human nutrition, Chapter 6 - Nutritional inhibitors and toxic factors, FAO Food and Nutrition Series, No. 27, ISBN 92-5-103381-1.
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Let us not forget exactly how goitrogens affect the thyroid:
When you eat brassica vegetables, glucosinolates are broken down by the digestive system. The breakdown of some of those glucosinolates such as progoitrin produces a compound known as goitrin, which has been found to interfere with the thyroid's ability to use iodine. Also, the digestive breakdown of another class of glucosinolates, known as indole glucosinolates, results in the release of thiocyanate ions, which also impede the thyroid from using iodine.
Another argument put forward by those who favour brassica vegetables is the following:
“No human study has demonstrated a deficiency in thyroid function from consuming cruciferous vegetables.”
Certain human cultures that consume a high goitrogenic diet have indeed been studied to discover why they suffer a high incidence of thyroid problems. But a study that involves imposing on humans the regular consumption of goitrogenic foods as a staple would be considered unethical knowing that goitrogens harm the thyroid. Therefore there are no long-term peer-reviewed studies of this nature involving humans.
Any credible study of human consumption of BV's would need to take place over at least several months or a year and be compared against a similar group of people who eat non-brassica plant-based foods. To knowingly impose a risk of an underactive thyroid of hypothyroidism on fellow humans in this way would not be regarded as acceptable.
However, much laboratory research using animals and human lab samples has established beyond any doubt that goitrogens can and do affect the thyroid by slowing it down. This is not disputed by anybody. Furthermore, several animal studies and human field studies show unequivocally that the regular consumption of goitrogenic foods as a staple leads to an underactive thyroid and other health problems. Here is an abridged extract from some review studies carried out by FAO (United Nations):
"....the incidence of goitre in animals and humans with normal dietary intake of iodine suggests there are other factors in the aetiology of simple goitre. The observation that cabbage feeding produced thyroid hyperplasia in rabbits was the first milestone of progress in this field.....The isolation and identification [of goitrogens in] some foods in the Cruciferous family led to the search for similar agents in more commonly eaten foodstuffs. [For example goitrogens] in cassava tubers, a staple of tropical Africa, was implicated in the high incidence of goitre in human cassava-eating populations". Source: FAO United Nations, Sorghum and millets in human nutrition, Chapter 6 - Nutritional inhibitors and toxic factors, FAO Food and Nutrition Series, No. 27, ISBN 92-5-103381-1.
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"Brassica species containing goitrogens include cabbage, broccoli, cauliflower, rutabaga, kohlrabi, and the oilseeds, rapeseed and canola. Feeding rapeseed meal with high glucosinolate levels to animals and poultry induces enlarged thyroids, reduced circulating thyroid hormones, liver, kidney, and adrenal abnormalities, and poor growth and reproductive performance.
One study showed no ill effects when volunteers ingested 40 mg goitrin/day in Brussels sprouts over a 4-week period. Another study showed inhibition of iodine uptake after administration of 50-200 mg of goitrin. Studies in Great Britain estimated an average intake of 76 mg glucosinolate per person per day, with a range of up to 200 mg per day. Whether or how much the consumption of Brassica vegetables contributes to ill health in humans is unknown. The cause of endemic goiter in certain geographic regions may be the result of the interaction between iodine deficiency and certain food components, such as glucosinolates.
In summary, glucosinolates are known to be goitrogenic in animals, but their role in inducing goiter in humans is less clear".
Source: Bernadene Magnuson, Ph.D., University of Idaho, Dept. of Food Science and Toxicology, 1997, http://extoxnet.orst.edu.
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In the above Magnuson review of several studies it was clearly established that feeding goitrogenic food to animals caused underactive thyroid and other serious illnesses. Since then, other animal studies have shown similar results. If goitrogens in foods are bad for animals, they will be equally bad for humans. Our human biology is not fundamentally different to other types of animal mammalian biology.
Note: it takes several weeks (more than a month) for an underactive thyroid or for hypothyroidism to set in because it takes this long to test any rise in TSH (thyroid-stimulating hormone). TSH is higher in a thyroid that is under-performing. The reference to a 4-week study in the above Magnuson review is therefore unreliable and suspect.
Mary Shomon was diagnosed with thyroid disease in 1995 and is now an internationally known patient-advocate for combating thyroid disease. She is the founder and editor-in-chief of several thyroid, autoimmune, and nutrition newsletters as well as a popular thyroid disease website, www.thyroid-info.com. Here is an abridged extract of what she has to say about eating brassica vegetables.
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Goitrogens are naturally-occurring substances found in various foods, and they have the ability to cause a goiter; an enlargement of the thyroid gland.
In addition to promoting goiter formation, goitrogenic foods can act like anti-thyroid drugs, slowing down the thyroid, and ultimately causing hypothyroidism, an underactive thyroid.
Goitrogens are able to disrupt normal thyroid function by inhibiting the body’s ability to use iodine, block the process by which iodine becomes the thyroid hormones thyroxine (T4) and triiodothyronine (T3), inhibit the actual secretion of thyroid hormone, and disrupt the peripheral conversion of T4 to T3.
The key goitrogen-rich foods are the vegetables in the cruciferous category. In addition, there are a number of other foods that contain significant amounts of goitrogens.
For the general public, overconsumption of raw goitrogens may be able to slow down the thyroid, and/or promote development of a goiter. (Important note: raw juicing often includes goitrogenic vegetables like cabbage and spinach, and these juices end up providing highly concentrated amounts of goiter-promoting ingredients.)
You should be careful not to over-consume large quantities of goitrogenic foods. This does not mean you need to avoid your favorite foods however. The enzymes involved in the formation of goitrogenic materials in plants can be at least be partially destroyed by heat, allowing you to enjoy these foods steamed or cooked*.
* Note from author: if you cook the food long enough to destroy its goitrogenic glucosinolates, you will also destroy its nutritional content. If you cook the food lightly so as to preserve nutrition, you will also preserve the goitrogenic glucosinolates. So to argue that you can destroy goitrogens in brassica vegetables and hence enjoy their consumption is not so because any nutritional content will also be destroyed. You would be eating nutritionally dead food. Also, note that over-cooked food often contains harmful compounds created by the cooking process itself. Furthermore, regular cooking does not remove any significant amount of harmful phytates and oxalates because they are not heat sensitive.
If you are a heavy consumer of cooked goitrogens, however, and have a difficult time balancing your thyroid treatment, you may consider cutting back on the amount of goitrogenic foods in your diet. Note that soy falls into the general category of goitrogens, but beyond the goitrogenic properties, it has other abilities as a phytoestrogen to affect thyroid function, whether you have a thyroid gland or not.
(Source: Mary Shomon, All About Goitrogens - Why Thyroid Patients Are Warned About Cruciferous Vegetables, article posted at www.thyroid.about.com and reviewed by a USA board-certified physician)
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Kale, a brassica vegetable, is mistakenly highly regarded by some. Teresa Fung, Sc.D., M.S., an adjunct professor of nutrition at the Harvard School of Public Health and a professor at Simmons College in Boston, confirms the kale-thyroid link. But, she says, “normal, reasonable amounts of eating should not be a problem. A regular person [with no thyroid issues] who eats several servings of cruciferous vegetables a week should not have problems. It’s the dose that makes a poison. If people have hypothyroidism or they’re taking thyroid medication, then they should check with their doctor. But even in this case, reasonable amounts shouldn’t be a problem. Now, if people have a tall glass of kale juice every single day, then it gets into the unknown [hypothyroidism] territory.”
In the above statement Dr. Fung is right to say that you should go easy on kale because of its goitrogenic effect. And clearly it's the dose that makes a poison. But why consume kale in any amounts given its goitrogenic potential?
As discussed in this book, BV's are generally nutritionally poor compared to most other plant-based foods. Furthermore, kale is high in harmful phytates and oxalates, so why put your health at risk?
But we cannot escape from phytates and oxalates. These antinutrients are nothing to fear if consumed in small amounts, if you are perfectly healthy and if you stick to a wholly nutritious diet. But most people are not perfectly healthy and do not stick to a wholly nutritious diet, thus becoming vulnerable to antinutrients.
An important reason for avoiding BV's relates to weight gain. As explained in this book, BV's are a major cause of weight gain if consumed as a regular staple. Remember that an underactive thyroid can cause many health problems even if you don't have full blown hypothyroidism.
An underactive thyroid is a very common condition throughout the world, and it must be the world's biggest hidden cause of obesity. It is 'hidden' because it is silent and insidious and most people do not realize they have an underactive thyroid. Furthermore, the consumption of BV's amounts to a silent health plague that affects millions of people. Such people are not aware that BV consumption is to blame for their poor health. Simply give up BV's and replace them with other plant-based foods of which you have a wide choice.
When the thyroid slows down, this directly affects the adrenal glands. "The two glands [thyroid and adrenals] work together to supply essential hormones and deliver them where they need to be throughout the body" (source: Beth Orenstein, Cynthia Haines, MD, The Link Between Hypothyroidism and Adrenal Fatigue, www.everydayhealth.com).
So as a result of an underactive thyroid, the adrenals glands are inhibited from issuing hormones that trigger weight loss. These six specific adrenal hormones (let's call them 'lipo hormones') switch on lipolysis. That is, they switch on a process that allows fat cells to release stored body fat into the bloodstream for burning as energy. When the adrenals are inhibited from producing lipo hormones, this switches off lipolysis and fat cells accumulate fat instead of losing fat.
There is plenty of solid evidence showing that low-carb and calorie-restriction diets cause an underactive thyroid, which in turn causes weight gain. You simply cannot lose weight if you have an underactive thyroid. Equally, when regular BV consumption causes an underactive thyroid this can have a dramatic effect on weight gain.
You are urged to see an excellent video at YouTube which explains this in detail. The video is titled "Is Your Thyroid Making You Fat?" Click on the following image to go there now:
For general good health and a slim body you need to be in a state of lipolysis as often as possible. Lipolysis is the easiest and quickest way to lose surplus body fat in a safe and healthy manner.
Clearly the avoidance of BV's is one thing you can do to help switch on lipolysis. But there are several other things you can easily do to fully exploit lipolysis, the body's own natural weight loss weapon. For more information on this subject please see our sister book: The Lipo Diet - the lipolysis breakthrough for permanent weight loss (DeliveredOnline.com).
If you currently eat BV's as a staple (i.e. every day), you will notice a dramatic improvement in your health after about six weeks of giving up these harmful vegetables. The improvement in health will be gradual as your thyroid returns to normal little by little.
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Thank you for your interest in this subject and for taking the time to read this book. If you know anybody who eats broccoli, cabbage or other brassica vegetables, please do refer them to this book (you will be doing them a great service). For the most up-to-date version of this book please go to www.deliveredonline.com. Any comments relating to this book are most welcome. Please email: mailto@deliveredonline.com (making sure you just put the title 'Don't Eat Your Broccoli' in the subject line).
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