Flashback Friday: How to Avoid Lectin Poisoning

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

In the 1800s, a compound was discovered in castor beans, which we would come to know as the first of a class of lectin proteins—natural compounds found throughout the food supply, but concentrated in beans, whole grains, and certain fruits and vegetables. Every decade or two, in the popular literature, and the medical literature, a question is raised whether dietary lectins are causing disease. It’s easy to raise hysteria about lectins. After all, that first one, found back in 1889, went by the name ricin, known to be “a potent homicidal poison”, used by the Kremlin to assassinate anti-Communist dissidents—or by rogue chemistry professors, for that matter. And, ricin is a lectin. Thankfully, however, “many lectins are non-toxic, such as those [found in] tomatoes, lentils,…and other common foods.” And, even the ones that are toxic—like those found in kidney beans—are utterly destroyed by proper cooking.

But, you can’t eat raw kidney beans. If you do, you’ll be doubled over with nausea, vomiting, and diarrhea within hours, thanks to the lectins, which would otherwise be destroyed by adequate cooking. How do you even eat raw kidney beans, though? I mean, the only way they’re sold uncooked is as dried beans, and they’re like little rocks. Well, in the first reported outbreak, “an impromptu supper was made” with a bag of beans dumped in a skillet, and soaked in water overnight, but never cooked. You can’t even just throw dried beans in a slow cooker. Dried kidney beans have to be boiled. Kidney beans should be soaked in water for at least five hours, and then boiled for at least ten minutes. Ten minutes? Kidney beans wouldn’t be done in just ten minutes.  Exactly. Yeah, cooking presoaked beans for a couple minutes can destroy the lectins, but it takes like an hour of boiling before they’re edible, before you could, you know, flatten them easily with a fork. So, the lectins would be long gone before they’re palatable.

Without presoaking, it takes 45 minutes in a pressure cooker to get rid of all the lectins, but an hour to make kidney beans edible. So basically, “[i]t appears that cooking beans to the point where they might be considered edible is more than sufficient to destroy virtually all [lectin] activity.” Even 12 hours at 65 Celsius won’t do it, though, which is like the temperature of a hot cup of tea. But, you can tell they weren’t done—still firm and rubbery, though you can imagine someone putting those in like some “raw” vegetable salad, and that could make people sick. And, it has, with dozens of incidents reported—all of which could have been “easily prevented” had the beans been soaked overnight, drained, and then boiled for at least ten minutes. Or, if they would have just eaten canned beans. Canned beans are cooked beans; the canning process is a cooking process. “None of the confirmed incidents [were] due to canned beans.”

We’ve known since the early 60s that “conventional cooking methods [can] effectively destroy” lectins in beans, and therefore, “it is possible to ignore any human…problems that could be associated with lectins from properly processed legumes.” So yeah, you can show that feeding lectins to rats isn’t good for them, or to cell tissues in a petri dish. But, in these articles that claim dietary lectins may be “disease causing toxicants”, the only negative effect they can find on humans are those raw and undercooked kidney bean incidents. Do dietary lectins cause diseases of affluence? How about we test that hypothesis? So, they “performed a trial on 24 domestic pigs”, and a paleo-pig diet beat out cereal-based swine feed. Could they not find any people willing to eat paleo?

In response to one such review of the evidence, based largely on laboratory rodents, one peer-reviewer cautioned that we should not draw conclusions about the involvement of dietary lectins in the cause “of diseases without definite and positive proof.” That was written more than a quarter century ago, and such clinical proof has yet to materialize. What we do have, however, is ever-growing evidence that legumes—beans, split peas, chickpeas, and lentils—are good for us, associated with a longer lifespan, a significantly lower risk of colorectal cancer (a leading cancer killer), considered part of “a natural, cost-effective, and free from side effects solution for the prevention and treatment of [type 2 diabetes].” Randomize people to eat five cups of lentils, chickpeas, split peas, and navy beans a week, and you can see the same benefits in terms of weight loss and metabolic benefits that you do with caloric-restriction portion control. And, the whole lectins theory is based on lectin-containing foods being inflammatory.

But, prescribe four servings a week of legumes, packed with lectins, and get a significant drop in C-reactive protein—in fact, a 40% drop of this leading indicator of systemic inflammation, eating more beans.

The purported “plant paradox” is that on one hand, whole healthy plant foods are the foundations of a good diet, yet we supposedly need to avoid beans, and whole grains, and certain fruits and vegetables, because of the evil lectins. But, if you look at the actual science, all whole plant foods are associated with decreased mortality—meaning the more of them people ate, the longer people tended to live. And, this includes lectin-filled foods, such as whole grains and beans. So, maybe there’s really no paradox, after all.

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Image credit: Kristina DeMuth. Image has been modified.

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