Are Lectins in Food Good or Bad for You?

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

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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.

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 to a powder, and then dust it on their 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% of the lectins are gone after boiling for just 15 minutes, and all gone by half an hour. And indeed, when they tested the white beans, toasting for three minutes didn’t do a thing; no wonder people got sick, whereas 95% of the lectins were inactivated after boiling them for three minutes, and completely inactivated after ten. Evidently, “’Do not eat raw beans’ is a traditional admonition in Japan to [avoid] 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, “[l]ow doses of lectins may be beneficial by stimulating gut function, limiting tumour 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 [prevention] (and possibly treatment) of colon…cancer.” Or, of course, we could just eat our vegetables.

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 Mass General found a substance in wheat germ—the lectin in whole wheat—which appeared “to be tumor cell specific”—clumping together “the tumor cells, while the normal cells” were left almost completely alone. 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, you can effectively predict the presence of polyps and cancers.

And subsequently, it was discovered that lectins couldn’t just distinguish between the two, but extinguish the cancer cells, while largely leaving the normal cells alone. For example, that same white kidney bean lectin was found to almost completely suppress the growth of human head and neck cancer cells, liver cancer cells, breast cancer cells, and (at least most of the way) cervical cancer cells—within about three days. But, this was in a petri dish. That’s largely the basis of the evidence for the antitumor activity of plant lectins—these petri dish studies. How do we even know that dietary lectins are absorbed into the body?

Colorectal cancer is one thing. I mean, 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.” Or, even more exciting, the potential for effectively rehabilitating cancer cells. “[T[he loss of differentiation and invasion are the…hallmarks of malignant [tissues]”—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; colon cancer cells become less colon-like.

And, 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. Here’s the before picture: cancer cells just growing in amorphous clumps. But then, here’s those same cancer cells after two weeks exposed to the fava bean lectins. The cells have started to go back to growing glandular structures, like normal colon tissue. Therefore, dietary lectins, or putting them in a pill or something, “may slow the progression of colon cancer[s],” 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 the digestive tract?

“Although lectin-containing foods [like beans and whole grains] are frequently consumed cooked or otherwise processed, these treatments may not always [completely] 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. Yeah, but are we able to absorb the lectins into our system? Yes. Within an hour of consumption of raw or roasted peanuts, you can detect the peanut lectin in the bloodstream of most people. Same thing with tomatoes. Some of the non-toxic lectin in tomatoes also makes it down into our gut and into our blood. The wheat lectin, known as WGA, the wheat germ agglutinin, doesn’t seem to make it into our bloodstream, though, even after apparently eating the equivalent of more than 80 slices of bread’s worth of wheat germ! And, if you ate something like pasta, the boiling 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 “allow[ing] 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. But look, we know 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.”

Now, they could just be eating fewer carcinogens. But, plants do have all those active components that do seem to protect against the “initiation, promotion, [and] progression of cancer.” And so, maybe lectins are one of those protective compounds. Look, we know people who eat more beans and whole grains tend to get less cancer overall; we’re just not sure exactly why. Now, you could say, who knows? Who cares? Well, Big Pharma cares. You can’t make as much money on healthy foods as you can on “lectin-based drugs.”

Please consider volunteering to help out on the site.

Image credit: Kristina DeMuth. Image has been modified.

Motion graphics by Avocado Video. 

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.

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 to a powder, and then dust it on their 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% of the lectins are gone after boiling for just 15 minutes, and all gone by half an hour. And indeed, when they tested the white beans, toasting for three minutes didn’t do a thing; no wonder people got sick, whereas 95% of the lectins were inactivated after boiling them for three minutes, and completely inactivated after ten. Evidently, “’Do not eat raw beans’ is a traditional admonition in Japan to [avoid] 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, “[l]ow doses of lectins may be beneficial by stimulating gut function, limiting tumour 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 [prevention] (and possibly treatment) of colon…cancer.” Or, of course, we could just eat our vegetables.

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 Mass General found a substance in wheat germ—the lectin in whole wheat—which appeared “to be tumor cell specific”—clumping together “the tumor cells, while the normal cells” were left almost completely alone. 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, you can effectively predict the presence of polyps and cancers.

And subsequently, it was discovered that lectins couldn’t just distinguish between the two, but extinguish the cancer cells, while largely leaving the normal cells alone. For example, that same white kidney bean lectin was found to almost completely suppress the growth of human head and neck cancer cells, liver cancer cells, breast cancer cells, and (at least most of the way) cervical cancer cells—within about three days. But, this was in a petri dish. That’s largely the basis of the evidence for the antitumor activity of plant lectins—these petri dish studies. How do we even know that dietary lectins are absorbed into the body?

Colorectal cancer is one thing. I mean, 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.” Or, even more exciting, the potential for effectively rehabilitating cancer cells. “[T[he loss of differentiation and invasion are the…hallmarks of malignant [tissues]”—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; colon cancer cells become less colon-like.

And, 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. Here’s the before picture: cancer cells just growing in amorphous clumps. But then, here’s those same cancer cells after two weeks exposed to the fava bean lectins. The cells have started to go back to growing glandular structures, like normal colon tissue. Therefore, dietary lectins, or putting them in a pill or something, “may slow the progression of colon cancer[s],” 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 the digestive tract?

“Although lectin-containing foods [like beans and whole grains] are frequently consumed cooked or otherwise processed, these treatments may not always [completely] 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. Yeah, but are we able to absorb the lectins into our system? Yes. Within an hour of consumption of raw or roasted peanuts, you can detect the peanut lectin in the bloodstream of most people. Same thing with tomatoes. Some of the non-toxic lectin in tomatoes also makes it down into our gut and into our blood. The wheat lectin, known as WGA, the wheat germ agglutinin, doesn’t seem to make it into our bloodstream, though, even after apparently eating the equivalent of more than 80 slices of bread’s worth of wheat germ! And, if you ate something like pasta, the boiling 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 “allow[ing] 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. But look, we know 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.”

Now, they could just be eating fewer carcinogens. But, plants do have all those active components that do seem to protect against the “initiation, promotion, [and] progression of cancer.” And so, maybe lectins are one of those protective compounds. Look, we know people who eat more beans and whole grains tend to get less cancer overall; we’re just not sure exactly why. Now, you could say, who knows? Who cares? Well, Big Pharma cares. You can’t make as much money on healthy foods as you can on “lectin-based drugs.”

Please consider volunteering to help out on the site.

Image credit: Kristina DeMuth. Image has been modified.

Motion graphics by Avocado Video. 

Doctor's Note

This is the last in a three-video series on lectins. Missed the first two? Check out 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.

Beans are a food group I highly recommend. For all of the most recent videos on beans, check out the topic page. 

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