Are Lectins in Food Good or Bad for You?

Might lectins help explain why those who eat more beans and whole grains have less cancer?

Lectins are to blame for the great “white kidney bean incident” of 2006 in Japan. One Saturday evening, a TV program introduced a new method to lose weight. The method was simple: toast some dry, raw, white kidney beans in a frying pan for three minutes, grind the beans into a powder, and then dust it onto rice. Within days, a thousand people fell ill, some with such severe diarrhea and vomiting they ended up in the hospital. Why? Lectin poisoning. Three minutes of dry heat is not enough to destroy the toxic lectins in kidney beans. If you don’t presoak them, you need to boil large kidney beans for a full hour to completely destroy all the lectins, though if you first soak them overnight 98 percent of the lectins are gone after boiling for just 15 minutes and all are gone by half an hour, as you can see at 0:44 in my video Are Lectins in Food Good or Bad for You?. And, indeed, when researchers tested the white beans, they found that toasting them for three minutes didn’t do a thing. It’s no wonder people got sick. But, 95 percent of the lectins were inactivated after boiling them for three minutes and completely inactivated after ten minutes of boiling. Evidently, “‘Do not eat raw beans’ is a traditional admonition in Japan to prevent intestinal problems”—and now we know why.

While canning may completely eliminate lectins from most canned beans, some residual lectin activity may remain in canned kidney beans, though apparently not enough to result in toxicity. And, ironically, “How doses of lectins may be beneficial by stimulating gut function, limiting tumor growth, and ameliorating obesity.” What? I thought lectins were toxic.

For as long as people have speculated dietary lectins are harmful, others have conjectured that they may be protective. “If this theory is correct, appropriate lectins by mouth should be of use in the prophylaxis [prevention] (and possibly treatment) of colon cancer.” Or, of course, we could just eat our beans.

Interest in the purported antitumor effect of plant lectins started with the discovery in 1963 that lectins could distinguish between cancer cells and normal cells. Researchers at Massachusetts General Hospital found a substance in wheat germ—the lectin in whole wheat—that appeared to be “tumor cell specific,” clumping together the tumor cells, while the normal cells were left almost completely alone. In fact, it is so specific that you can take a stool sample from someone and, based on lectin binding to the colon lining cells that get sloughed off into the feces, effectively predict the presence of polyps and cancers.

Subsequently, it was discovered that lectins couldn’t only distinguish between the two types of cells, but also extinguish the cancer cells, while largely leaving the normal cells alone. For example, that same white kidney bean lectin, as you can see at 2:53 in my video, was found to almost completely suppress the growth of human head and neck cancer cells, liver cancer cells, breast cancer cells, and cervical cancer cells (at least most of the way), within about three days—but that was in a petri dish. Those petri dish studies are largely the basis of the evidence for the antitumor activity of plant lectins. How do we even know dietary lectins are absorbed into our body?

Colorectal cancer is one thing. The fact that lectins can kill off colon cancer cells in a petri dish may be applicable, since lectins we eat may come in direct contact with cancerous or precancerous cells in our colon, “providing a mechanism” by which bean consumption may help in “the prevention and treatment of colorectal cancer.” Even more exciting is the potential for effectively rehabilitating cancer cells. The “loss of differentiation and invasion are the histological hallmarks of malignant cells,” meaning that when a normal cell transforms into a cancer cell, it tends to lose its specialized function. Breast cancer cells become less breast-like, and colon cancer cells become less colon-like. What these researchers showed—for the first time—is that the lectin in fava beans could take colon cancer cells and turn them back into looking more like normal cells. As you can see at 4:13 in my video, before exposure to the fava bean lectins, the cancer cells were growing in amorphous clumps. But, after exposure to the fava bean lectins for two weeks, those same cancer cells started to go back to growing glandular structures like normal colon issue. Therefore, dietary lectins or putting them in a pill “may slow the progression of colon cancer,” potentially helping to explain why dietary consumption of beans, split peas, chickpeas, and lentils appears to reduce the risk of colorectal cancer based on 14 studies involving nearly two million participants. Okay, but what about cancers outside of the digestive tract?

“Although lectin containing foods,” like beans and whole grains, “are frequently consumed cooked or otherwise processed, these treatments may not always inactivate the lectins…For example, lectins have been detected in roasted peanuts….” Peanuts are legumes, and we don’t tend to eat them boiled but just roasted or even raw. Are we able to absorb the lectins into our system? Yes. As you can see at 5:12 in my video, within an hour of consumption of raw or roasted peanuts, you can detect the peanut lectin in the bloodstream of most people. Same with tomatoes. Some of the non-toxic lectin in tomatoes also makes it down into our gut and into our blood. Wheat germ agglutinin, the wheat lectin known as WGA, doesn’t seem to make it into our bloodstream, though, even after apparently eating the equivalent amount of wheat germ in more than 80 slices of bread. And, if you ate something like pasta, the boiling in the cooking process might wipe out the lectin in the first place anyway.

In terms of phytochemicals in the fight against cancer, lectins are able to “resist digestion resulting in high bioavailability,” potentially allowing “the cellular mechanisms of the host to utilize the full potential of the…dramatic anti-cancer benefits” lectins have to offer. But, these dramatic benefits have yet to be demonstrated in people. We do know, however, that population studies show “that the consumption of a plant-based diet is strongly associated with a reduced risk of developing certain types of cancer.” People eating a plant-based diet could just be eating fewer carcinogens, but plants do have all those active components that do seem to protect against the “initiation, promotion, or progression” of cancer. So, maybe lectins are one of those protective compounds. We know people who eat more beans and whole grains tend to get less cancer overall, but we’re just not sure exactly why. Now, you could say, “Who cares why?” Well, Big Pharma cares. You can’t make as much money on healthy foods as you can on “lectin based drugs.”

Interested in learning more about lectins? Check out my videos Dr. Gundry’s The Plant Paradox Is Wrong and How to Avoid Lectin Poisoning.

Lectins remind me of the story about phytates. Other components of beans and whole grains, phytates were thought at first to be harmful, but, more recently, evidence is coming to light that suggests the opposite may be true. Check out Phytates for Rehabilitating Cancer Cells and Phytates for the Prevention of Osteoporosis.

What else may explain the protective effect of beans? See, for example, Gut Dysbiosis: Starving Our Microbial Self. Soybeans may be particularly protective against certain cancers, as you can see in BRCA Breast Cancer Genes and Soy.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

How to Avoid Lectin Poisoning

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.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

Is White Rice a Yellow-Light or Red-Light Food?

Arsenic is not just considered to be a carcinogen; it’s also designated as a “nonthreshold carcinogen, meaning that any dose, no matter how small, carries some cancer risk”—so there really isn’t a “safe” level of exposure. Given that, it may be reasonable to “use the conservative ALARA” approach, reducing exposure As Low As Reasonably Achievable.

I have a low bar for recommending people avoid foods that aren’t particularly health-promoting in the first place. Remember when that acrylamide story broke, about the chemical found concentrated in french fries and potato chips? (See my video Acrylamide in French Fries for more.) My take was pretty simple: Look, we’re not sure how bad this acrylamide stuff is, but we’re talking about french fries and potato chips, which are not healthy anyway. So, I had no problem provisionally bumping them from my list of yellow-light foods into my red-light list, from “minimize consumption” to “ideally avoid on a day-to-day basis.”

One could apply the same logic here. Junk foods made out of brown rice syrup, rice milk, and white rice are not just processed foods, but also arsenic-contaminated processed foods, so they may belong in the red zone as red-light foods we should avoid. What about something like whole brown rice? That is more difficult, because there are pros to help outweigh the cons. I discuss this in my video Is White Rice a Yellow-Light or Red-Light Food?, where you can see a graphical depiction of my traffic light food system at 0:49.

The rice industry argues that the “many health benefits of rice consumption outweigh any potential risk,” which is the same sentiment you hear coming out of Japan about the arsenic-contaminated seaweed hijiki: Yes, “the cancer risk posed by hijiki consumption exceeds this acceptable [cancer risk] level by a factor of 10,” an order of magnitude, but the Japanese Ministry of Health stresses the “possible health benefits,” such as lots of fiber and minerals, as if hijiki was the only weed in the sea. Why not choose any of the other seaweeds and get all the benefits without the arsenic? So, when the rice industry says the “many health benefits of rice consumption outweigh any potential risk,” it’s as if brown rice was the only whole grain on the planet. Can’t you get the whole grain benefits without the risks by eating oatmeal, barley, or quinoa instead? Or, is there some unique benefit to rice, such that we really should try to keep brown rice in our diet?

Consumer Reports recommended moving rice to the yellow-light zone—in other words, don’t necessarily avoid it completely, but moderate your intake. The rice industry, in a fact sheet entitled “The Consumer Reports Article is Flawed,” criticized Consumer Reports for warning people about the arsenic levels in rice, saying “[t]here is a body of scientific evidence that establishes…the nutritional benefits of rice consumption; any assessment of the arsenic levels in rice that fails to take this information into account is inherently flawed and very misleading.” The rice industry cites two pieces of evidence. First, it asserts that rice-consuming cultures tend to be healthier, but is that because of, or despite, their white rice consumption? And what about the fact that rice-eating Americans tend to be healthier? Perhaps, but they also tend to eat significantly less saturated fat. So, once again, how do we know whether it’s because of—or despite—the white rice?

The rice industry could have cited the study I discuss at 3:12 in my video that showed that brown rice intake of two or more servings a week was associated with a lower risk of diabetes, but presumably, the reason it didn’t is because intake of white rice is associated with an increased risk of diabetes, and white rice represents 95 percent of the U.S. rice industry. Switching out a third of a serving of white rice a day for brown rice might lower diabetes risk by 16 percent, but switching out that same white rice for whole grains in general, like oats or barley, might work even better! So, other grains have about ten times less arsenic and are associated with even lower disease risk. No wonder the rice industry doesn’t cite this study.

It does cite the Adventist studies, though, and some in vitro data. For example, in a petri dish, as you can see at 4:05 in my video, there are rice phytonutrients that, at greater and greater doses, can inhibit the growth of colon cancer cells while apparently leaving normal colon cells alone, which is exciting. And, indeed, those who happened to eat those phytonutrients in the form of brown rice once or more a week between colonoscopies had a 40 percent lower risk of developing polyps. (The consumption of green leafy vegetables, dried fruit, and beans were also associated with lower polyp incidence.) But, the only reason we care about the development of polyps is that polyps can turn into cancer. But, there had never been studies on brown rice consumption and cancer…until now, which I discuss in my video Do the Pros of Brown Rice Outweigh the Cons of Arsenic?.

For those unfamiliar with my traffic light system, I talk about it in my book trailer. Check out How Not to Die: An Animated Summary.

Almost there! This is the corresponding article to the 12th in my 13-video series on arsenic in the food supply. If you missed any of the first 11 videos, see:

Ready for the finale? See Do the Pros of Brown Rice Outweigh the Cons of Arsenic?.

And you may be interested in Benefits of Turmeric for Arsenic Exposure.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations: