GreenSmoothieGirl Logo
Lose 10 Pounds in 10 Minutes. Add 10 Years to your life.
Our beautiful template for infinite variety of greens and superfoods in your smoothies—print this and eliminate the need for recipes! Get it now for free!

Goitrogens and Thyroid

Panic! Are cruciferous vegetables’ goitrogens killing my thyroid?

My customer support wrote me that people constantly write us “freaking out” about a widely circulated article on the internet saying that cruciferous vegetables essentially damage your thyroid gland. Crucifers include broccoli, kale, cabbage, and cauliflower.

People are susceptible to fear and paranoia—which are antithetical to empowerment and faith. I’ve written about this in Ch. 1 of 12 Steps to Whole Foods, but I need to take a stronger stand, since it’s Top Five (questions I am asked, via email and everytime I speak in public).

As with food-combining theories (D’Adamo, etc.), or the idea that too many of one green food is “toxic” (Boutenko), or the idea that oxalates in greens harm us (another dubious internet-circulated claim)… reaction is like that line from Jerry Maguire, “Show me the money!”

My variation on that quote is, “Show me the data!”

Evidence that cruciferous vegetables are phenomenally powerful anti-cancer foods is voluminous. They also reduce bad estrogens; this is desperately needed by Americans, as we’re daily bombarded with endocrine disruptors (“bad estrogens”). David Wolfe, in fact, says his favorite supplement of 2011 is Indole-3-Carbinol (I3C), which is an extract of the crucifers. I’ve been taking it myself.

The evidence that one compound in crucifers may have deleterious effects? It’s limited and sketchy at best.

If we can isolate one compound (of dozens, maybe 100 or more) in green foods, and say that Compound X has Effect Y on Gland Z, how do we know that Compounds A, B, and C don’t have mitigating effects on Effect Y? How do we know that the profoundly healing properties of Compounds D, E, and F in that same food don’t work together synergistically with Compound X? The mountain of evidence that vegetables prevent disease suggests that foods are far more than the sum of their parts. Science still has little understanding of why plant foods are powerful, although in general, scientific communities like to break things down into parts and explain phenomena inductively. Let’s back up and use some deductive reasoning.

The “articles” on the internet (read: people saying stuff—let’s not give them undue credit by calling them articles) claim that LARGE AMOUNTS can damage the thyroid and increase the need for iodine. The entire American diet does both of those things—first, damage the thyroid, and second, increase the need for iodine (for instance, we eat salt stripped of iodine in virtually all our foods– or that refined salt has chemical isolates of a toxic form of iodine put back in). So I’m highly skeptical of how any researcher isolated the “goitrogen” factor. Somebody please show me where that’s been done.

Pick on the REAL bad guys here. Are we really going to flog cabbage and broccoli, when 95% of Americans are eating nuggets boiled in grease made of dozens of disease-infested chicken “parts” that if you looked at them each separately, you would wrinkle your nose and throw it in the garbage? And the same 95% are drinking tubs full of brown chemical liquids infused with carbon dioxide that contain absolutely no food?

A reader, Shawna, wrote us an email with tons of capitalized sentences and exclamation points, saying, “Hey! I’ve been doing green smoothies for a few years now! And I’m hypothyroid! Help—am I killing my thyroid?”

Me, too—except it’s been 17 years, not 3. My thyroid was all but destroyed because of nuclear fallout at the Nevada test site in the late 60’s when I was a baby, drinking highly radioactive milk from cows who ate the radioactive fallout on the grass even hundreds of miles away.

I eat massive quantities of greens and doing so has restored my thyroid into perfect balance. (I do take a very small amount of bioidentical thyroid—it’s natural, not a drug. I recommend looking into that if you’re on a synthetic hormone drug.)

Ask your health-care practitioner specializing in natural solutions if iodine supplementation is right for you. For many or even most Americans, it is quite necessary. This may give you peace of mind if you are worried that your crucifers consumption is “high,” since the theory is that goitrogens cause the thyroid to have insufficient iodine available.

If you’re worried about it, try to avoid eating “large quantities” of raw cruciferous vegetables (i.e. cabbage, kale, broccoli, cauliflower). I seriously doubt anyone is eating “large quantities” anyway. We really don’t have an overconsumption” problem with any vegetable, here in the Western world, unless fries and potato chips count.

Even Wikipedia’s definition of crucifers warns against “high intake,” but what is that, exactly? I wish not only that I could find the research backing the goitrogen claim, but also the definition of “high intake”!

I welcome any response to this, but I’ve been unable to find that. Which begs the question, who came up with all of this anyway? Mary Shomon quotes the claim (I have and read her books), and Sally Fallon repeats it too (I have and read hers too). Sally has a master’s degree in English, and Mary has a bachelor’s degree—neither are researchers or medical professionals.

Where is the science? Since I can’t find it, I have to draw the conclusion that the avalanche of data that crucifers are powerful foods that prevent disease must outweigh the “goitrogen” claim.

(These sources also tell us that we should BOIL our broccoli or kale for 30 minutes to get rid of goitrogens. Who would eat a vegetable boiled for 30 mins?! Sometimes I really wonder about people passing along ridiculous advice like this on the internet. Even if you can gag it down, don’t forget you’ve killed EVERYTHING beneficial in the cauliflower/broccoli if you nuke it to mush like that. Enzymes, minerals, vitamins—gone.)

Everywhere I look, the claims all seem to point back to the Weston A. Price Foundation. And the WAPF seems to have taken down its statements that started this whole thing. All the links are broken, including the one and only link from Wikipedia backing this bold claim about crucifers harming the thyroid. Is that because they figured out that 50 years of research documenting the positive effects of kale, broccoli, bok choy, and Brussels sprouts might dwarf that unsupported claim? Maybe too many people asked them to prove it, which got embarrassing.

I would be going far too sideways to take on the WAPF right now, but suffice it to say I’m disappointed with their knee-jerk reaction to anything that comes out, valid research included, in defense of a plant-based diet or in criticism of eating lots of meat. That foundation is at the heart of supporting a heavily meat-based diet, and they came out, guns blazing, against the Oxford-Cornell China Project, within days of its release in the form of The China Study (2004).

WAPF (or Sally Fallon, one of its most significant authors) advocates for eating fermented vegetables. I’m a champion of that, too, but their extreme stand against raw vegetables is mystifying to me. (I like Sally Fallon and some of the things she teaches. Not all. Is it even realistic to convince Americans to eat 100% homemade FERMENTED vegetables–when they’re currently eating virtually none of any kind besides iceberg lettuce, fried potatoes, and ketchup?)

And while indigenous cultures all over the world eat various types of fermented foods (a WAPF tenet)—they eat plenty of plain raw (or cooked) vegetables too. Some of the extremist positions within WAPF fly in the face of three things: newer research, modern lifestyle reality, and logic.

When someone makes a claim that impresses you as conflicting with a lot of other data you’ve been exposed to, make them prove it to you. Don’t change your lifestyle till they do.

Just TRY to find the evidence about goitrogens killing your thyroid, on the internet or in books/journals. Not claims—EVIDENCE. Then write us at if you find anything compelling. See if you can find DOZENS of studies, like you can find for crucifers being powerful, medicinal, high-fiber foods.

Meantime, here’s my suggestion based on the preponderance of evidence. Eat lots of greens, the widest variety you reasonably can, considering seasonal issues, budget, and your time. (Don’t panic if you eat spinach several days in a row—I eat it almost every day!) Don’t eat excesses of it—just eat it in moderate amounts in a balanced diet containing a variety of other greens, vegetables, fruits, legumes, grains, nuts and seeds. But definitely enjoy broccoli, kale, radishes, etc.

If you aren’t hypothyroid, don’t concern yourself with this issue at all. If you are, know the goitrogenic foods and don’t eat more than reasonable quantities.

The George Mateljan Foundation is one of my favorite sources—they do a great job of bringing all the research together and do not have agendas or profit motives. They say that “…carefully controlled research studies have yet to take place on the relationship between goitrogenic foods and thyroid hormone deficiency…” and note that “healthcare practitioners differ greatly on their perspectives as to whether a person who has thyroid problems, and notably a thyroid hormone deficiency, should limit their intake of goitrogenic foods.”

They state that even among hypothyroid patients, there’s wide variability in how we will react to a certain compound in food, and little is known about it. Mateljan goes out on a limb and says a serving of goitrogenic foods a few times a week should not be a problem for thyroid-depressed people:

I believe this issue is yet another “tempest in a teapot” that I hope doesn’t keep you up at night. Eat a variety of whole foods, mostly (or all) plants, and let your fear, along with your “disease” (symptoms) slip away.


If you’re wanting to know more about what I’ve been referring to in my analysis herein, here are excerpts of the goofy stuff in the article (all repeated from Sally Fallon claims) that had our friend Shawna panicking, and writing us IN ALL CAPS with lots of !!!! punctuation:

“When raw crucifers are chewed, or when microwaved and steamed crucifers are digested by intestinal bacteria, they release substances called goitrogens that increase the need for iodine when consumed in small amounts and can damage the thyroid gland when consumed in large amounts.”

“These goitrogens also inhibit the transfer of iodine into mother’s milk.”

[Robyn’s note: I think they copied this virtually verbatim from Wikipedia. However, anyone can change anything in Wiki. The only link corroborating this claim is broken, and it comes from the WAPF, of course.]

“Steaming crucifers until they are fully cooked reduces the goitrogens to one-third the original value on average. Since release of the goitrogens from steamed crucifers depends on intestinal bacteria, however, the amount released varies from person to person.”

“Boiling crucifers for thirty minutes reliably destroys 90 percent of the goitrogens.”

[Robyn’s note: I’ve already commented on this. Boiling a vegetable for 30 minutes renders it not only light in goitrogens, but also dead, and completely inedible.]

“Fermentation does not neutralize the goitrogens in crucifers. When foods like sauerkraut are consumed as condiments, however, the small amount of goitrogens within them is not harmful if one’s diet is adequate in iodine.”

“An increased dietary intake of iodine compensates for the consumption of moderate amounts of crucifers but cannot reverse the effects of large amounts of crucifers.”

[Robyn’s note: no definition of “moderate” and “large” amounts? Where were people studied who eat “moderate” and “large” amounts? IS there anyone eating a large amount? We aren’t exactly prying people away from platesful of kale.]

“Paradoxically, the goitrogens found in crucifers may offer some protection against cancer. The jury is still out on whether or not this is true.”

[The jury is out? Dozens of studies for decades now have documented that. The jury deliberating on this “goitrogen” issue hasn’t even convened yet.]

“The use of sauerkraut as a condiment and several servings of steamed crucifers per week is probably beneficial. People who consume more than this amount, especially lactating mothers, should be sure to obtain extra iodine in their diet from seafood. People who make liberal use of crucifers on a daily basis should boil a portion of them to avoid excessive exposure to goitrogens.”

“It reminds me off another issue with cabbage, it reduces the milk supply of nursing mothers. A dear friend of mine was trying to include healthy food in her diet during the flu season, so started adding some raw cabbage to her daily salad. Within a week or so, she couldn’t figure out why her nursing son was wanting to nurse all the time and was obviously hungry. She has mentioned the issue with milk supply to me, but it wasn’t until I was over at her house for lunch that it clicked. She was making us a salad and chatting about how she added cabbage to her salad everyday. The light dawned!”

[Robyn’s note: She went to lunch at her friend’s house and a conversation proved which, of various complex factors, decreased the friend’s milk supply? This is not exactly scientific.]

“I feel that they [cruciferous vegetables] also aren’t as digestible raw anyways.”

[Robyn’s note: What does this mean? Where is the evidence of this? Where is the discussion of the role of enzymes in “digestibility?”]

Skip to content