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:

Dr. Gundry’s The Plant Paradox Is Wrong

A book purported to expose “hidden dangers” in healthy foods doesn’t even pass the whiff test.

I started getting emails about The Plant Paradox, a book purporting to expose “the hidden dangers in ‘healthy’ foods that cause disease and weight gain”—foods like beans, whole grains, and tomatoes. Hidden dangers? The author’s talking about lectins in a rehashing of the discredited Blood Type Diet from decades ago. I reviewed it a while ago in my video Blood Type Diet Debunked, but it just keeps coming back. The Plant Paradox was written by an MD, but if you’ve seen my medical school videos including Physicians May Be Missing Their Most Important Tool, you’ll know that is effectively an anti-credential when it comes to writing diet books, basically advertising to the world that they’ve likely received little or no formal training in nutrition. Dr. Atkins was, after all, a cardiologist. Even when we give the benefit of the doubt, the problem is it doesn’t even seem to pass the sniff test, as I discuss in my video Dr. Gundry’s The Plant Paradox Is Wrong.

If lectins are bad, then beans would be the worst, so bean counters would presumably find that bean eaters cut their lives short. But, the exact opposite may be true, with legumes—beans, split peas, chickpeas, and lentils—found to be perhaps “the most important dietary predictor of survival in older people” in countries around the world. As Dan Buettner pointed out in his Blue Zones work, lectin-packed foods are the “cornerstones” of the diets of all the healthiest, longest-lived populations on the planet. Plant-based diets in general and legumes, the most lectin-lush of foods, in particular are a common thread among longevity Blue Zones around the world, as you can see at 1:30 in my video.

If lectins are bad, then whole-grain consumers should be riddled with disease when in fact “whole grain intake is associated with a reduced risk of coronary heart disease,” the number one killer of men and women, “cardiovascular disease, and total cancer, and mortality from all causes” put together. This means that people who eat whole grains tend to live longer and suffer from fewer “respiratory diseases, infectious diseases, diabetes, and all non-cardiovascular, non-cancer causes” to boot. And, this is not only the case in population studies. As I showed in my video Can Oatmeal Help Fatty Liver Disease?, you can randomize people into whole grain interventions and prove cause-and-effect benefits. It’s the same with tomatoes. When you randomize women to a cup and a half of tomato juice or water every day, all that nightshade tomato lectin “reduces systemic inflammation” or has waist-slimming effects, reducing cholesterol as well as inflammatory mediators.

So, when people told me about The Plant Paradox, I thought to myself: Let me guess. He sells a line of lectin-blocking supplements. And, what do you know? His Lectin Shield capsules “assist your body in the fight against lectins” for only $79.95 a month. That’s only about a thousand dollars a year—a bargain for “pleasant bathroom visits.” Then, of course, there are ten other supplements for sale, so for only $8,000 or $9,000 a year, you can lick those lectins. Let’s not forget his skincare line. “Firm + Sculpt” for an extra $120 a month, which is all so much more affordable when you subscribe to his VIP club.

Look, people ask me all the time to comment on a new blog, book, or YouTube video, and I remind them that a hundred thousand peer-reviewed scientific papers on nutrition are published in the medical literature every year and we can barely keep up with those. But because people continually emailed me about this book, I decided I’d give it a chance.  He tells us to “forget everything you thought you knew was true.” (Diet books love saying that.) Okay. Ready? Chapter 1, citation 1: “Eating shellfish and egg yolks dramatically reduces total cholesterol.” What?! Egg yolks reduce cholesterol? What is this citation? I’ve linked the paper he cites on shellfish consumption so you can see it for yourself. By now, you know how these studies go. How do you show a food decreases cholesterol? Remove so much meat, cheese, and eggs that, overall, saturated fat falls—in this case, about 50 percent, as you can see at 4:15 in my video. If you cut saturated fat in half, of course cholesterol levels are going to drop. So, the researchers got a drop in cholesterol after removing meat, cheese, and egg yolks, yet that’s the paper he uses to support his statement that “egg yolks dramatically reduce[d] cholesterol.” That’s unbelievable! That’s the opposite of the truth. As you can see at 4:36 in my video, the truth is if you add egg yolks to people’s diets, their cholesterol goes up. How dare he say otherwise? What’s more, it’s not like he’s spewing some harmless foolishness, like saying the Earth is flat. Heart disease is the number one killer of men and women. His claims could actually hurt people.

So much for my giving him the benefit of the doubt.

This is an unusual article for me. I normally try to stay out of the so-called diet wars and just stick to bringing you the latest science. Roughly 100,000 papers are published on nutrition in the peer-reviewed medical literature every year, and we have a hard enough time keeping up with them, but let me know what you think: Would you like me to allocate time to more of these types of reactive discussions?

You’ll note I never really addressed Dr. Gundry’s thesis about lectins, but I do exactly that in these two videos: How to Avoid Lectin Poisoning and Are Lectins in Food Good or Bad for You?.


Here are links to the videos I alluded to in this article, if you want to learn more:

What else can tomatoes do? See Inhibiting Platelet Activation with Tomato Seeds.

One of the key reasons whole grains may be so beneficial is their effect on our good bacteria. Check out Gut Microbiome: Strike It Rich with Whole Grains and Microbiome: We Are What They Eat to learn more.

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 Reduce Your TMAO Levels

Should we be concerned about high-choline plant foods such as broccoli producing the same toxic TMAO that results from eating high-choline animal foods such as eggs?

Choline- and carnitine-rich foods—meat, eggs, and dairy—can be converted by our gut flora into trimethylamine, which in our livers is then turned into TMAO, a toxic compound that may increase our risk of heart failure, kidney failure, and atherosclerosis, or heart attacks and strokes. The good news, though, is that this “opens up exciting new nutritional and interventional prospects” for prevention, as I discuss this in my video How to Reduce Your TMAO Levels.

Okay, so how do we do it? Well, if our gut bacteria can take meat, dairy, and eggs and turn them into TMAO, all we have to do is…destroy our gut flora! We could give people antibiotics to eliminate the production of TMAO. However, that could also kill our good bacteria and “facilitate the emergence of antibiotic-resistant bacterial strains.”

What about probiotic supplements? Maybe if we add good bacteria, they will crowd out the ones that take the meat, egg, and dairy compounds and turn them into the TMA that our liver turns into TMAO. But, that doesn’t work. Adding good bacteria doesn’t seem to get rid of the bad. What if we added new bacteria that could somehow siphon off the TMA made by the bad bacteria? Well, there’s a bacterium inside the guts of cows and sheep that turns trimethylamine into methane. Could we use that bacterium to get rid of some of the trimethylamine from our gut, like a cow fecal transplant? There’s a problem with that. If it didn’t take, you’d have to keep giving it to people: “Continuous administrations may be necessary if subjects do not become colonized.” So, might the fact that Consumer Reports found fecal contamination in every sample of beef it tested be a good thing? No. Methane-producing bacteria may be able to eat up our TMAO, but, unfortunately, these bacteria may be associated with a variety of diseases, from gum disease down to colorectal cancer, as you can see at 2:15 in my video.

If antibiotics and probiotics aren’t going to work to prevent gut bacteria from taking meat, dairy, and eggs and turning them into the trimethylamine, which our liver makes TMAO out of, I guess we have no choice but to cut down on…our liver function!

That was the billion-dollar answer to cholesterol. The same foods—meat, dairy, and eggs—raise our cholesterol, but dietary change isn’t very profitable. So, the drug industry developed statin drugs that cripple the liver’s enzyme that makes cholesterol. Could “pharmacologic inhibition” of the enzymes in our liver that make TMAO “potentially serve as a therapy for CVD [cardiovascular disease] risk reduction”? Trimethylaminuria is a genetic condition in which this enzyme is naturally impaired, in which there is a build-up of trimethylamine in the bloodstream. The problem is that trimethylamine is so stinky it makes you smell like “dead fish.” So, “given the known adverse effects…from sufferers of fish odor syndrome, the untoward odorous side effects of inhibiting this enzyme make it a less attractive [drug] target.”

Do we have to choose between smelling like dead fish or suffering from heart and kidney disease? If only there were some other way we could stop this process from happening. Well, what do those with trimethylaminuria often do to cut down trimethylamine levels? They stop eating animal products.

About a third of those who complain of bad body odor despite good personal hygiene test positive for the condition, but reducing or eliminating meat, egg, and dairy intake can be a real lifesaver. But, given what we now know about how toxic the end product TMAO can be for normal people, cutting down on animal products may not just save the social lives of people with a rare genetic disorder, but help save everyone else’s actual lives.

The “simplest point of intervention” is to simply limit the consumption of foods rich in choline and L-carnitine, which “can be an effective strategy to limit circulating TMAO.” But, wait! We could always try to genetically engineer a bacterium that eats up trimethylamine, but “the simplest and safest recommendation” may just be to eat more healthfully. You can completely eliminate carnitine from the diet, since our body makes all we need, but choline is an essential nutrient so we do need some. Thankfully, we can get all we need in fruits, vegetables, beans, and nuts. “However excess choline, such as that found in eggs, may be worth avoiding.”

Need we worry about high-choline plant foods, like broccoli? Consumption of cruciferous vegetables is associated with a significantly longer life and less cardiovascular disease mortality, as you can see at 5:34 in my video. To see what was going on, researchers took the vegetable highest in choline, brussels sprouts, and had people eat two cups a day for three weeks. What happened? Their TMAO levels actually went down. It turns out that brussels sprouts appear to naturally downregulate that TMAO liver enzyme—not enough to make you stinky, but just enough to drop TMAO.

And, people who eat completely plant-based may not make any TMAO at all—even if you try. You can give a vegan a steak, which contains both choline and carnitine, and there will not even be a bump in TMAO because vegetarians and vegans have different gut microbial communities. If we don’t eat steak, then we don’t foster the growth of steak-eating bacteria in our gut. So forget the cow—how about getting a fecal transplant from a vegan? From a TMAO standpoint, we may not have to eat like a vegan as long as we poop like one.


Can you sense my frustration as I read paper after paper proposing those ridiculous (but profitable!) answers when the safe, simple, side-effect-free solution was staring them in the face the whole time? It makes me think of so many parallels, not the least of which are:

For more on TMAO, the “smoking gun” of diet-microbiome-disease interactions, see:

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: