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Sweden’s dietary guidelines are pioneering in many ways; for example, encouraging people to decrease their climate impact by choosing more plant-based foods, which tend to produce greatly fewer greenhouse gas emissions. But I was surprised by this page on the official Swedish National Food Agency website, which translates to cyanogenic glycosides and hydrogen cyanide, encouraging people to stay away from ground flax seed for fear of cyanide toxicity. As in the ground flax seeds I encourage everyone to eat every day. You can see why this was the first question I got when I spoke in Stockholm.

Was the Swedish government onto something? Had I just been duped by Big Flax-funded researchers who claimed you could eat pounds of ground flax seeds a day without worrying—more than 150 tablespoons a day? First, some background.

 As many as one in five plants that we eat produce cyanide. In fact, if you look at the major food crops in the world, more than half are “cyanogenic,” meaning cyanide producing. But unlike toxic elements, like lead, mercury, arsenic that can’t be broken down into anything, cyanide is an organic molecule—one carbon atom attached to one nitrogen atom. In this state, it can definitely be toxic, but broken down or complexed to something else, and it loses its toxicity. And we have an enzyme in our body that does just that: a “cyanide detoxifying enzyme.” And, that’s just one of “five main ways” our body can detoxify cyanide. It does require protein to do it, though; and so, that’s why you can read about chronic cyanide toxicity among malnourished populations in Africa trying to live off of improperly processed cassava root. But as long as we’re getting adequate protein in our diet, our body can detoxify the normal amounts of cyanide we eat every day.

Now there is a rare, congenital genetic condition called Leber’s disease, where you’re born without the ability to detoxify cyanide; and indeed, yeah you could go blind drinking apple cider or something, but otherwise our bodies evolved to be cyanide-detoxifying machines. But, obviously, there’s a limit. For example, a case of cyanide poisoning after “bitter almond ingestion.” Not regular almonds, which produce about 40 times less cyanide, but bitter almonds—which you can’t even buy. They’re used in flavor manufacturing. But, if you did, eating 50 of them could kill you, or even just a handful for a small child. This suggests that eating 2,000 regular almonds at one sitting could also be bad news.

You can’t buy bitter almonds, but you can buy apricots, and apricot kernels, which are the seeds inside the stone, actually have pretty toxic levels, and have indeed been implicated in cases of “severe cyanide poisoning,” all linked to the “Laetrile: the cult of cyanide,” “Promoting poison for profit” that I talked about previously; so, I’m totally sympathetic to regulators wanting to take a precautionary approach. But are flax seeds like bitter almonds, where just a few ounces could kill you, or more like regular almonds, where regular dietary intake wouldn’t even come close?

Although the fact that flax seeds can produce cyanide sounds like it would be “a significant health concern, it is not for several reasons,” says flax industry-funded scientists. “First, the adult human body has the ability to detoxify [up to 100 mg of cyanide per day].” That’s where they come up with their pounds of flaxseeds a day are safe number. And if you wanted to eat more than those totally unrealistic 150 tablespoons a day, you could just eat them in baked goods, since “cooking destroys [the] cyanide.” And, eating seven or eight tablespoons of raw flax seeds doesn’t even bump “urinary thiocyanate levels,” which is an indicator of cyanide exposure—so, it doesn’t even look like your body is exposed to it. “Thus, the toxicity of flax seed from [cyanogenic glycosides] is not, evidently, a realistic health threat.” Okay, let’s unpack that.

The cooking part is mostly true. Yes, bake muffins with even like a quarter-cup of ground flax each for 15 to 18 minutes at about 450 degrees Fahrenheit, and the cyanide-forming compounds are gone. Looks like the same thing happens with baked bread. But, bake ground flax seeds on their own, and even an hour at 350 degrees only wipes out 20 percent; though baking them whole wipes out 80 percent, and what, baking in bread or muffins wipes out 100 percent? How does that make any sense? It’s the moisture. It’s heat plus water that wipes out the cyanide. Boiling for just five minutes can wipe it out, like when making hot cereal or something. And so, yes, it’s true in most cases that cooking eliminates the cyanide compounds, because it typically starts out in a batter, as an egg substitute, or baking crackers; the dough starts out moist. And so, yes, in those cases the cyanide is gone upon cooking. But you can’t just spread ground flax seeds on a baking sheet, because they dry out so fast that only a minority of the cyanide is lost. But, look, why does it matter if your body doesn’t even seem to notice seven or eight tablespoons of raw? But that’s not true. “Urinary thiocyanate excretion” doubled at that level, though that’s just a sign your body is actively detoxifying it. And if we can detoxify a kilo worth of flax a day, what’s the problem?

Well, even if the “adult human body has the ability to detoxify up to 100 mg of cyanide a day,” first of all, kids eat flax too. Second of all, a kilo has more than the 100 you said we could detoxify—about 50 percent more—and, I’m not interested in how much we can detoxify “up to.” For safety, you’re interested in the worst-case scenario, not the best-case scenario. Would someone please just give people different doses of flax seeds and just measure how much cyanide ends up in their blood? But that’s never been done… until now, which we’ll cover next.

“Flaxseed [packs] a nutritional punch,” and, as a bonus, the release of cyanide from flax seed is “below [a] toxic lethal dose.” Well, I should hope so. Back-of-the-envelope type calculations have led industry-funded scientists to assert that “a person would have to consume eight cups…of ground flaxseed [at a time] to achieve acute cyanide toxicity.” I’d feel better, though, if it was actually put to the test.

Researchers tested flax seeds under “worse case [scenario] conditions with respect to resulting in higher cyanide levels in the blood.” So, “1”: locate the flax seed with the “highest level of cyanide”-forming compounds you can find. So, they went to stores and bought 15 different sources of flax seed, and though the average level was 140 milligrams per kilo, which is about typical, they did find one with 220, so they used that one. “2”: “maximal mechanical destruction” to release the most cyanide; so, they used some crazy 20,000 RPM lab grinder.“3”: eat it all at once on an empty stomach, and then keep the stomach empty. And, they gave it raw, since cooking can often wipe it all out. If the recommended daily dose is like one or two tablespoons of ground flax seed a day—I recommend one in my Daily Dozen checklist—they decided to go with four and a half tablespoons. Okay, so what happened?

The range of cyanide blood levels that one might estimate to possibly be associated with the “clinical symptoms of intoxication” would be like 20 to 40. So, that would be like here or higher, where we want to stay below. So, four and a half tablespoons on an empty stomach of the highest cyanide-containing ultra-ground raw flax seeds they could find and…the highest individual level rise was just under 14, and the average was down around six.

There has to be some amount of flax that takes you over the limit, though. So, they tested nine tablespoons, and 15 tablespoons too. Remember, we start to worry at around 20 to 40. Three and a half teaspoons of raw high-cyanide ground flax on an empty stomach? Hardly a blip. Seven teaspoons at a time? Same thing. Fourteen teaspoons (four and a half tablespoons) and there’s that six. Okay, but what about a little over nine tablespoons—that’s over a half-cup at a time—and that does start skirting toxicity. And finally, what about a whole cup? I don’t even know how you’d eat a whole cup at once, but that is too much, putting you in that potential toxic range for about three hours. So much for the industry’s eight-cups-at-a-time-are-safe. But even in this worse-case scenario situation, one cup raw on an empty stomach at the highest dose they could find, that person still didn’t actually have any clinical symptoms. This is consistent with the fact that there’s not a single published report of cyanide poisoning after consumption of flax seeds anywhere in the literature, even from Swedish health spas, where they evidently give up to 12 tablespoons as a “fibre shock.” Usually, high doses are two or so tablespoons three times a day, and this dose would be “safe with respect to possible acute toxicity of cyanide.”

Okay, but what about any possible chronic toxicity? The World Health Organization has something called the “PMTDI”—the “provisional maximum tolerable daily intake.” It’s defined as the amount you can eat safely, every day, for the rest of your life, without risking any adverse health effects, based on the best available data—though often, that’s just like rat studies, as it was in this case. If you put varying doses of cyanide in the drinking water of rats for a few months, at a certain level, the so-called benchmark dose lower confidence limit, there’s a 10 percent increased incidence of shrinkage of the tail of the epididymis, which is where sperm is stored in the testicles. That happens at the human equivalent of about 150 tablespoons of flax seeds a day worth of cyanide. But, they want to err on the side of caution, so they introduce “a 100-fold uncertainty factor” to create the PMTDI. So, instead of 150 tablespoons of flaxseeds a day, the average American should stick to under 1.5 tablespoons a day if you’re going to eat them every day. So, my tablespoon-a-day Daily Dozen recommendation should be safe by any of these standards.

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