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How should we properly cook beans?

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, a question is raised in both the popular literature and the medical literature as to whether dietary lectins are causing disease, which I discuss in my video How to Avoid Lectin Poisoning.

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 and by rogue chemistry teachers on TV. 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.

You can’t eat raw kidney beans anyway. If you do, you’ll be doubled over with nausea, vomiting, and diarrhea within hours, thanks to the lectins that would otherwise have been “destroyed by adequate cooking.” But how would you even eat raw kidney beans? The only way they’re sold uncooked is as dried beans, which are 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 put dried beans in a slow cooker. Dried kidney beans have to be boiled. In fact, it has been “recommended that kidney beans should be soaked in water for at least 5 h[ours] followed by boiling in fresh water for at least 10 min[utes] before its consumption.” Ten minutes? Kidney beans wouldn’t be done after only ten minutes. Cooking presoaked beans for a couple of minutes can destroy the lectins, but it takes about an hour of boiling them before they’re edible, before you can flatten them easily with a fork. So, the lectins would be long gone before the beans are even 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 of the…activity of lectins.” Even cooking them for 12 hours at 65 degrees Celsius, which is like the temperature of a cup of hot tea, won’t do it, though. But, you could tell they weren’t done, “being a firm rubbery texture,” though you can imagine someone might put those in a “raw” vegetable salad, which could make people sick. And, it has, with dozens of incidents reported over the years. They could have been easily prevented had the beans been soaked overnight, drained, and then boiled for at least ten minutes, or if canned beans had been eaten instead Canned beans are cooked beans; the canning process is a cooking process. “None of the confirmed incidents was due to canned beans.”

We’ve known since the early 1960s that conventional cooking methods can effectively destroy lectins in beans. Therefore, “it is possible to ignore any human nutrition-related problems that could be associated with lectins from properly processed legumes.” So, while you can show that feeding lectins to rats isn’t good for them or to cell tissues in a petri dish, in the articles that claim that dietary lectins may be “disease causing toxicants,” the only negative effect they can find in humans are those raw or undercooked kidney bean incidents. Do dietary lectins cause “diseases of affluence”? Researchers tested that hypothesis by performing a trial on 24 domestic pigs, and a paleo pig diet beat out “a 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 no 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 and are associated with a longer lifespan; significantly lower the risk of colorectal cancer, a leading cancer killer; and are considered part of a “natural, cost-effective, and free from side effects solution for the prevention and treatment of T2DM [type 2 diabetes].” Randomize people to eat five cups of lentils, chickpeas, split peas, and navy beans a week, and you see the same 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, when researchers prescribed four servings a week of legumes, packed with lectins, they found a significant drop in C-reactive protein, which you can see at 5:10 in my video. They found a 40 percent drop in this leading indicator of systemic inflammation by eating more beans.

The purported “plant paradox” is that, on the one hand, whole healthy plant foods are the foundation of a good diet, yet, on the other hand, we supposedly need to avoid beans, 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, as you can see at 5:36 in my video. So maybe there’s really no paradox after all.

Plant paradox? If you missed it, that was the subject of my video Dr. Gundry’s The Plant Paradox Is Wrong. And—spoiler alert!—there’s even evidence to suggest lectins may be good for you. See Are Lectins in Food Good or Bad for You? to learn more.


Speaking of paradoxes, you may be interested in The Hispanic Paradox: Why Do Latinos Live Longer?.

What about beans, beans, the musical fruit? See my blog post Beans and Gas: Clearing the Air.

In health,

Michael Greger, M.D.

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