Just an FYI from Chris Masterjohn, a PHD in Nutrition (long):
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Thyroid hormone is the central governor of the LDL receptor, and the LDL receptor is, in turn, the central governor of clearance of LDL cholesterol from the blood. And basically thyroid is a messenger who is communicating that we are in a state of abundance, we have all of the food and nutrients that we need, and it is time to utilize those nutrients for the purposes of reproduction, high physical performance, and other things of that nature. And cholesterol is the precursor to a lot of these key hormones, like the sex steroids, for example, and the bile acids that improve digestion. So, thyroid hormone basically communicates to our cells that all of these nutrients that we need are available, so our cells respond by taking in LDL cholesterol from the blood and making lots of good things out of it, like testosterone, for example. Now, one of the key things that can happen when people start increasing their intake of fruits and vegetables and decreasing their intake of grains, which is a common dietary shift in the Paleo community, for example, is that you can increase your intake of plant goitrogens. Goitrogens are named because they have the ability to cause goiter, which is a problem that occurs as a response to insufficient thyroid hormone, and basically these plant chemicals have the ability to decrease the production or activation of thyroid hormone. Now, in most of the cases, I don’t want to suggest that eating these plants is a bad thing. In most of the cases, all you need to do to compensate is increase your intake of iodine. But in certain cases, if someone is not eating iodized salt, for example, and they’re living in an area where the iodine quality of the soil is poor, and they’re not eating seafood, which is the most reliable source of iodine, they may not be getting the iodine that they need to deal with that level of plant chemicals in the diet. So, it’s not that the plants are intrinsically bad. It’s just that we need to achieve that dietary balance. So, the number of plant chemicals in the plant kingdom that inhibit thyroid function, at least in a sort of test tube assay, is almost innumerable. I mean, there are thousands of plant chemicals. Basically all of the polyphenolics — the flavonoids, for example — they basically all inhibit the enzymes of thyroid hormone. But a lot of these plant chemicals don’t really make it into the system because we detoxify them properly, and sometimes they also even have beneficial effects. So, what we need to do is look at some of the areas where there is really convincing research done either in humans or in laboratory animals showing that certain foods, in the absence of adequate iodine, can contribute to decreased thyroid function.
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There are a few different classes of goitrogenic foods, and the way preparation affects them is different depending on the class. The most common that people on an ancestral diet are probably going to be eating is crucifers. So, crucifers, for example, include broccoli, brussels sprouts, cauliflower, cabbage, collard greens, kale, kohlrabi, mustard, rutabaga, turnip, bok choy, arugula, horseradish, wasabi, watercress, maca, and even canola oil is a crucifer.
crucifers have natural pesticides called glucosinolates, and these can be metabolized when we chew the crucifer or when we chop them up and so on. So, whether we’re eating them raw or cooked, we’re gonna get some of these goitrogens. And basically what happens is there’s an enzyme that frees a chemical called isothiocyanate, and then in our bodies we metabolize this to thiocyanate, and thiocyanate decreases the uptake of iodine into the thyroid gland because it basically competes with it. So, if you have a high ratio of isothiocyanate to iodine, then isothiocyanate actually gets into the thyroid gland. It also gets into breast milk, and it crosses the placenta in place of iodine. And then once it’s in the thyroid gland, it will compete for the utilization of the enzyme that makes thyroid hormone.
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Thiocyanate, you can completely protect against it simply by getting enough iodine in your diet. Now, a lot of people think that cooking or fermenting cruciferous vegetables is going to get rid of the goitrogens, but that is not true. Fermenting actually activates them. It actually does the conversion to the thiocyanate right in the jar of sauerkraut. So, if you’re eating sauerkraut and kimchi, you are not getting rid of the goitrogens. That doesn’t mean the foods are bad, but it means that you need more iodine when you’re eating those foods. If you steam the vegetables, it decreases the goitrogen yield about 30%, but it leaves about 70% of them there. Not only that, but when you steam the vegetables, the rate of liberation of the true goitrogens in the intestines varies fourfold between different people depending on their intestinal flora, so steaming is not a reliable way of getting rid of them. If you boil them for a half an hour and you keep the water, for example, in a soup, then that gets rid of 65% of the goitrogens, so about two-thirds. And if you get rid of the water, then that gets rid of about 90%, so if you boil them and then you pour the water out. Now, I don’t think that you need to go through all this extensive boiling. I think you just need to increase your iodine. But you have to realize if you have marginal iodine status and then all of a sudden you start eating sauerkraut and kimchi at every meal and then steaming broccoli for dinner, then that may push you over the edge into a frank iodine deficiency if you were on the border.
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So, what’s the dose of iodine that’s required to prevent, you know, a moderate intake of goitrogenic foods like we’re talking about now in the context of a Paleo or Primal type of diet from inhibiting thyroid function?
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Unfortunately, that has not been well characterized, but I think if we’re looking at the RDA, we’re looking at about — I think the RDA is still 150 mcg, and there are people out there who are using 50 mg, so I suspect that if you were taking 1 mg, for example, then that should be well more than sufficient to take care of the goitrogens themselves. But again, like you said, with environmental bromine exposure and so many other things, it’s possible that people may need more than that. But I think if we’re just talking about goitrogens, then that should be enough.
A minimal dose? Some other foods: another common food is cassava, which also goes by tapioca, manioc, yuca; flax; lima beans; and the fruits of all of the Rosaceae family, which includes cherries, almonds, plums, peaches, apricots, pears, raspberries, strawberries — these all contain cyanogenic glycosides, and sweet potatoes also contain a pretty small amount. Now, most of these foods come in different levels of bitterness, and in the more bitter varieties, that’s where you get more of the cyanogenic glycosides, and in the less bitter and more sweet varieties it’s less common. But these are also a source of thiocyanate because they actually release cyanide, and we detoxify the cyanide to thiocyanate, and it has all of the same effects as crucifers. And the most reliable way to detoxify these is to crush the foods and leach them in running water for a few days.
This becomes a key issue when you are consuming massive amounts of these. There are some people, for example, you know, certain populations where they rely on cassava for the main starch.
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So, again, I don’t think that these are going to be a major problem unless you’re adding it on top of the crucifers and on top of the low iodine intake. And the two others are soy and millet. I don’t think that people who are, you know, eating the Weston Price or Paleo ways are really going overboard with soy, but there is a myth out there that fermentation decreases the goitrogens, and it doesn’t. It does the opposite; it increases their bioavailability. So, if you add some fermented soy on top of everything else with low iodine, that can be a problem. And probably the most goitrogenic food in the world is millet, and this could be a problem if people are getting rid of gluten and they start eating a lot of gluten-free bread that’s made from millet, for example. And millet basically inhibits every step of thyroid metabolism, and high iodine intakes cannot overcome the effect of millet. But again, if it’s a minor component of the diet, it’s probably not a problem, but when you’re compounding it with all of these other foods and a low iodine intake, that’s when it can really be an issue. So, I think the solution to all of this is to eat these foods in moderation. Don’t go crazy with them. You know, don’t get the Vitamix out and load it with as many cruciferous vegetables as you can and drink cruciferous vegetable juice all day long. There are people who do that and suffer the consequences. You know, eat these foods in moderation, and make sure that you compensate for their inclusion in the diet with eating more seafood, perhaps some occasional seaweed, and if you need it — you know, you get the iodine test that you do, for example — if you need more iodine, supplement to bring that level up to where it needs
And I don’t think it’s going to be a problem as long as you have adequate iodine in your diet. I mean, a cup of cruciferous vegetables is not a lot. In all honesty, I sometimes, you know, I’ll eat a whole plateful of kale or something like that, so I don’t think it makes any difference if you just throw it in the juicer. But what I mean is if people are juicing so that they can consume exorbitant quantities of these vegetables compared to what they would be able to eat if they were eating them whole, that’s where you get the problem.
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This is the key issue: It’s an individual thing. Like I said, steaming, the goitrogen yield varies, you know, fourfold between different people, and different people have different iodine status. So, I am not saying these foods are bad. I’m saying that if you have symptoms of hypothyroidism when you made a dietary shift towards including more of these foods, then you might suspect those foods and their balance with iodine to be a culprit.
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A lot of studies show that selenium can protect against the potentially negative impacts of iodine supplementation for people who have autoimmune thyroid disease. So, if you do have Hashimoto’s or Graves’ or something like that and you’re considering taking iodine, you want to make sure that you’re getting at least 200 mcg of selenium combined from food and supplements each day.
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Though, in general, it’s always the better idea if possible to get as much of your nutrients from food, and that helps avoid this kind of thing, because there’s a lot we still don’t know about nutrient supplementation or augmentation.
And in a normal diet, you would get that mix because plants have selenomethionine and animal foods have selenocysteine.
And Brazil nuts, for those of you that don’t know, are a very rich source of selenium. They’re also very high in omega-6, but I don’t think that’s necessarily a problem because you only really need to eat two or three Brazil nuts, depending on the source, to get 200 mcg of selenium.
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