A goitrogen is a substance that suppresses the function of the thyroid gland by inhibiting iodine uptake, and these things are called goitrogens because they tend to cause goiter, which is a swelling of the thyroid gland. Some foods have been shown to be goitrogenic when they’re eaten in excess or if the person’s background intake of iodine is low. These are things like cassava, which is otherwise known as yuca, that’s how I usually talk about it; soy products; millet; sweet potatoes; cruciferous vegetables like cabbage, broccoli, Brussels sprouts, cauliflower, bok choy; and then most of the dark leafy greens like kale and collard greens.
In this episode, we cover:
5:52 How goitrogens can suppress thyroid function
9:44 How to cook vegetables
14:43 How oxalates can cause inflammation
Full Text Transcript:
Steve Wright: Hey, everyone. Welcome to another episode of the Revolution Health Radio Show. This show is brought to you by ChrisKresser.com. I’m your host, Steve Wright from SCDlifestyle.com, and with me is integrative medical practitioner and New York Times bestseller, healthy skeptic, Chris Kresser. Chris, how are you doing?
Chris Kresser: I’m great. How are you, Steve?
Steve Wright: I’m doing good. We’re doing this one earlier and earlier in the day. We’re trying to figure out how our brains work.
Chris Kresser: It’s a little early, and I have my coffee, my cream carrier here, otherwise known as coffee! And that’s breakfast for the time being, in case you were wondering.
Steve Wright: I’ll cheers you with my black coffee.
Chris Kresser: Right. So how are things with you, Steve?
Steve Wright: Things are good. Just getting back from a good trip back to Michigan to see the family, and that was a lot of fun. How’s everything going with your new program that you’re working on?
Chris Kresser: Yeah, the 14Four. It was great. Last week we recorded in studio. I was in a video studio we were using to record all the videos for the program. We have weekly videos for each week of the program but also some exercise demos and some stress management audio and video demos, a five elements qigong set that I demonstrated, and I’m super excited about the program. I think it’s going to help a lot of people. This program is really all about implementation. In my book, Your Personal Paleo Code (published in paperback as The Paleo Cure in December 2014), I talk about personalization and why that’s so helpful over the long term, developing your own program of diet and lifestyle that meets your particular needs, and I really believe that’s true. On the other hand, some people just need a lot of support to get started because it’s hard to make diet and lifestyle changes in the context of a really busy life and kids and family and work and everything that goes into modern life, so this program is all about giving people all the tools they need to make the transition to a healthy diet and lifestyle, really holding their hand every step of the way, and it’s also going to be a great reset for people. In the same way that people do Whole30s to kind of hit the reset button, I think this is going to be a great alternative to that because it’s a 14-day reset. It’s a little bit shorter, really accessible, but it also includes the important lifestyle elements like movement, stress management, and sleep, so it’s kind of like a whole body, whole lifestyle reset. It may even be ready by the time people are listening to this. I’m never sure when these podcasts air versus when we record them, but probably sometime in mid-August is when it will be available at least to people who are already subscribers, so I’m looking forward to it.
Steve Wright: Yeah, that sounds amazing. I think that’s going to be a great program. Coming off this trip back to Michigan, all my routines were all messed up, and so workout and stress reduction, all that stuff was kind of off the rails because just living in someone else’s house again and following different sets of rules, I’m happy to be back in Boulder here and back to my routines.
Chris Kresser: Yeah. That’s just life. It ebbs and flows. We’re on track, we’re off track, and so having something like this to come back to a few times a year is, I think, going to be great. I know I’m on the right track when my wife Elanne is bugging me to finish it so she can do one! I know I’m doing something right if that’s the case. She’s one of my toughest critics.
Steve Wright: Nice.
Chris Kresser: Well, we have a great question today. I think it’s relevant for a lot of people. Thyroid issues are definitely endemic… epidemic, rather, and seem to be increasing in frequency or commonality. Boy, I need to wake my brain up this morning. Another sip of coffee here! I can’t even talk! So, yeah, let’s listen to this question from Chris, and we’ll take it from there.
Question from Chris: Hi, Chris. This is Chris from the UK. I just had a question about cooking vegetables. I read a post that says when you cook cruciferous vegetables such as broccoli, cauliflower, cabbage, etc., that you should throw the water away if you steam them because of the goitrogens which block the thyroid and also when you’re cooking spinach and chard and things like that then there’s oxalic acid as well. I just wondered because I used to use the water to put into a stock I was making out of bones and for other things as well. And also if you put those vegetables into a casserole or something, then you’re obviously not going to be able to throw anything away because it’s going to be in that casserole, so I’d be surprised if it was actually a problem, and I’m thinking that’s just a bit of faux science. I would love to hear about maybe the best way to cook vegetables and what you can keep and what you can’t. Thank you.
Chris Kresser: OK. Great question, and I understand and applaud your skepticism, Chris, because there is a lot of faux science out there and what we might call voodoo science, but this actually is legitimate at least for some people, and I’m going to explain a little bit more about that now.
How goitrogens can suppress thyroid function
The two concerns Chris is referring to are goitrogens and oxalates. A goitrogen is a substance that suppresses the function of the thyroid gland by inhibiting iodine uptake, and these things are called goitrogens because they tend to cause goiter, which is a swelling of the thyroid gland. Some foods have been shown to be goitrogenic when they’re eaten in excess or if the person’s background intake of iodine is low. These are things like cassava, which is otherwise known as yuca, that’s how I usually talk about it; soy products; millet; sweet potatoes; cruciferous vegetables like cabbage, broccoli, Brussels sprouts, cauliflower, bok choy; and then most of the dark leafy greens like kale and collard greens.
At relatively low concentrations, if you eat these foods a few times a week, I don’t think it’s a problem, but if you start eating them more regularly and you eat them raw, which we’re going to come back to in a second, goitrogens can actually decrease the uptake of iodine in the thyroid gland from other foods that we eat that contain iodine. Now, this can typically be offset by supplementing with iodine or just eating more iodine-rich foods like sea vegetables or certain species of fish or fish head soup, things like that that are naturally high in iodine, but at higher concentrations, goitrogens interfere with the incorporation of iodine into thyroid hormone itself, and that means that even if there’s enough iodine going into the thyroid gland, it can’t be properly utilized and no amount of supplemental iodine either through food or supplements will be able to overcome that large intake of goitrogens.
Let’s imagine a scenario here where you have someone with hypothyroidism and they’re doing a green smoothie every day, and in that green smoothie they’re putting raw kale or collard greens and a fairly significant amount of those, and they’re doing that because maybe initially they feel good after they drink that, and they’re trying to get the nutrients from kale, and they’ve heard all about the power of green smoothies. What can happen to that person over time is that the goitrogens in the raw kale and collard greens will, as I said, inhibit uptake of iodine and start to make their hypothyroid condition worse, so raw kale green smoothies every day is a really bad idea for somebody with hypothyroidism. I feel like that message has gotten out a little bit recently but not to the extent that it needs to because I have a lot of patients who come and see me who are doing just that and they’re not aware of the potential effects on their thyroid gland.
Steve Wright: Now, would it be better, Chris, to be rotating through those greens, kind of like the one idea where if you’re consuming the same thing every day you’re going to be getting a high load of whatever’s in that, whether it’s one nutrient or one pesticide or whatever it is? Or is it the whole green leafy family that’s going to be dense enough in goitrogens that these people need to worry about that?
Chris Kresser: Well, definitely kale and collards are the biggest offenders. There are other green leafy vegetables that aren’t necessarily high in goitrogens or things that necessarily affect thyroid function, but I think the more important thing is if someone wants to have green smoothies, one thing you can do to at least reduce somewhat the potential goitrogenic effect of them is to steam the greens first.
How to cook vegetables
Cooking method affects the goitrogen content quite a bit of various foods. I mentioned yuca or cassava earlier, and cassava is one of the most goitrogenic foods there is raw. In fact, it has other toxins that are problematic when it’s eaten raw, and so it’s super important when you prepare yuca fries or eat yuca any other way that you boil it for at least 25 minutes before you do anything else with it because that boiling, when you discard the water, it reduces goitrogen content by, like, 90%, which is really significant obviously and makes it kind of a nonissue.
Steve Wright: With cooking or light steaming of the vegetables, I have to ask this because it’s something that I’ve wrestled with forever, which is that we know that that’s going to save you some antinutrients and help with the absorption of some of the nutrients, but we’re also sacrificing all of the phytonutrients, everything that can’t be heated. So is there something there that we should kind of flip flop back and forth?
Chris Kresser: Yeah, I don’t know that all of the phytonutrients are destroyed with steaming. Some of them will be, and there are plenty of nutrients that are still available and some that are going to be more available after they’re steamed compared to when they’re raw. With kale and other goitrogenic substances, if you steam, that reduces the goitrogen content by about one-third. Broccoli, other cruciferous vegetables, kale, collard greens, if you steam them lightly, that will reduce goitrogen content by 33%, which is significant, especially if you’re eating them fairly regularly.
Cooking also reduces the formation of other compounds in these vegetables that are goitrogenic called nitriles. Nitriles are actually even more goitrogenic than the goitrogens that we’re talking about themselves, and cooking has a greater impact on nitriles. Interestingly enough, fermentation, like fermenting cabbage into sauerkraut, actually increases the goitrogen content of sauerkraut, but it reduces by over half the amount of nitriles, and the effect of nitriles on thyroid function can’t be offset by iodine supplementation, so the net effect of fermenting cabbage is probably beneficial. In other words, sauerkraut is probably less problematic for thyroid than raw cabbage would be.
Steve Wright: Interesting. Huh.
Chris Kresser: So let’s take a step back and look at all this together. If you have thyroid issues, raw green smoothies every day are probably not a good idea. A green smoothie every day with some steamed greens? It depends. People are more or less susceptible to this effect. One thing to do would be to try that and see if you notice any difference in your thyroid symptoms: cold hands and feet, hair loss, dry skin, constipation, etc. People who have hypothyroidism know what those symptoms are. And if you experience an increase in those symptoms when you do that after a couple of weeks, it’s probably a sign that this happening. You can also use lab testing. You can test your TSH, your T4, and your T3 after maybe a month of doing that and see if you notice any changes in those markers. Some people will and some people won’t, which is why it’s hard to give a blanket recommendation. I would definitely, though, recommend against raw greens in the smoothies every day, and if you’re going to do them every day, go for the steamed greens and maybe include some other green leafy vegetables like spinach that aren’t necessarily high in goitrogens. However, spinach is high in something called oxalic acid or oxalates, and so we’re going to talk about that next because that was also part of Chris’ question.
Before I leave this topic, I want to say that pregnant women should be especially careful with the goitrogens because a developing baby has a really important need for adequate levels of thyroid hormone. Goitrogens can interfere with thyroid hormone uptake in the developing baby, and so I think pregnant women should definitely not do green smoothies with raw greens in them every day as a precaution and even may want to limit the steamed greens in smoothies to three times a week or something just to be careful.
How oxalates can cause inflammation
Oxalates, these are naturally occurring chemicals that are found in most plants, nuts, seeds, and they, like many toxins in plants, protect the plants from being eaten by bugs or just protect them in general. The highest food sources are okra, sweet potatoes, elderberry, fig, leeks, buckwheat, celery, spinach, and other leafy greens. For most people, oxalates are not really a problem, but there are some genetic defects in the enzymes that degrade oxalate that can cause a disease called primary hyperoxaluria that’s extremely rare. It’s like 1 to 3 people in a million, so it’s really unlikely that you have that condition. But there are other conditions that can elevate calcium or oxalate in the urine and increase the risk of calcium oxalate kidney stones, and this can happen if you’re deficient in magnesium because oxalic acid is readily oxidized and combines with calcium, iron, sodium, magnesium, and potassium, I think, to form these less soluble salts called oxalates, and then intestinal bacteria bring down oxalates so that they’re carried out in the feces. What that means is if your gut microbiota has been compromised or you suffer from leaky gut, these oxalates can enter your blood, turn into crystals, and then get stored in tissues, which causes pain and inflammation.
So once again, we see there’s no one-size-fits-all approach. Most people, especially if you have a healthy gut and no genetic mutations that predispose you to this, will be fine with oxalates in food, but if you have gut issues and particularly a permeable gut barrier, then oxalates can cause particularly muscle and joint pain and kind of overall inflammation. In that case, you would want to take it easy on all the foods that I just mentioned. There isn’t as much of an effect on cooking those foods with oxalate content that I’m aware of, so you just need to kind of mitigate your overall intake of those foods.
Steve Wright: If somebody thinks that they’re suffering with a load of oxalic acid in the body, would they try to supplement with more magnesium or calcium to try to help with that as well? Could that help?
Chris Kresser: Yeah, you definitely want to make sure your mineral balance is dialed in. You don’t want too many of those minerals, and you don’t want too few, but maybe doing some testing to see where you’re at on the mineral balance spectrum would be a good idea, and then supplementing with magnesium, in particular, can be helpful.
Steve Wright: Is there is a specific test that you like for calcium and magnesium?
Chris Kresser: That’s a good question. I tend to use the Genova or Doctor’s Data nutrient and elements test. I still look at them with a little bit of a grain of salt, I guess. I’m not 100% sold. It’s fairly complicated to test for minerals and vitamins because different minerals and vitamins are represented differently in the blood and the body tissues. Take magnesium, for example. When you do a serum magnesium test, which is typically what’s done on these tests, you get a certain reading back, but less than one-half of 1% of the magnesium that’s in the body at any given time is found in the serum. So the serum magnesium test only tells you what the status of a half a percent of your total body stores of magnesium is. And it would be wonderful if that was perfectly correlated to the other 99.5% of magnesium in your body, but it’s not. I mean, you can get some idea. If that’s low, it’s more likely that your body stores of magnesium are low, but it’s not a perfect correlation.
Steve Wright: And that’s also different than magnesium RBC readings, right?
Chris Kresser: Yeah, magnesium RBC is red blood cell, and that is another half percent of magnesium.
Steve Wright: We’re getting up there!
Chris Kresser: Yeah, but the other 99% of magnesium is stored inside cells in the tissue and the bone, and the only way to test for that, there is one test by a lab in Oregon, I think, where they do a cheek swab, and so they do a true intracellular magnesium test, but it costs $270 just for that test and often is not, in my opinion, worth it clinically. It’s better just to have the person take some magnesium because it’s safe to take and supplement with and see if their symptoms improve. That’s the issue with some of these mineral tests, and that’s not the only example. There are other examples of minerals and vitamins that are difficult to test for. Vitamin K2, for example, is very difficult to test accurately for. I know Chris Masterjohn has actually been working on an assay that would help get an accurate read on functional levels of vitamin K2. Some of the B vitamins, it’s actually more accurate to look at markers that are indirect that really tell us how much of the active form of that B vitamin is available, like methylmalonic acid for B12, which I’ve written about before, either in the blood or in the urine. Formiminoglutamic acid is a good sensitive marker for active folate deficiency. So it’s a great question, Steve, but actually the answer is not quite as cut and dried as we’d like.
Steve Wright: It never is with testing.
Chris Kresser: Yeah, exactly. So hopefully that was helpful. The takeaway, again, is that oxalates and goitrogens are not a problem for everyone. Goitrogens particularly are an issue for people with thyroid problems. Pregnant women should be aware of what we’ve discussed and follow those recommendations. And then oxalates can also be problematic for people with thyroid issues but more particularly people with genetic mutations that predispose them to not being able to break them down properly and also people with gut issues and who are experiencing muscle and joint pain and inflammatory conditions.
Steve Wright: Yeah, I’ve definitely seen some of those people. When you get a really inflamed gut, it definitely can complicate this a lot.
Chris Kresser: Yeah.
Steve Wright: Well, thank you, Chris. This has been an informative podcast. I love how we jumped down the testing rabbit hole for a little while there, and I think it sounds like the message once again is you just have to test and listen to your body.
Chris Kresser: Yep, that’s almost always the outcome.
Steve Wright: Awesome. Well, thanks, everyone, for listening. In between episodes, you can go to Facebook.com/ChrisKresserLAc and find some of the studies that Chris is reading and using to formulate these types of podcasts and blog posts and over at Twitter.com/ChrisKresser to catch up on what he’s tweeting over there. Thanks for listening, everyone. Thanks, Chris.
Chris Kresser: Thanks, everyone. Thanks, Steve. See you next time.
Steve Wright: See ya.