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:

Is Nutritional Yeast Healthy for Everyone?

Those with certain autoimmune diseases such as Crohn’s disease should probably not eat nutritional yeast.

Thousands of years ago, some yeast floated down into our flour and drinks, pleasing our palates, and we’ve been regularly exposed to it ever since. Yeast isn’t a problem for most people, but even non-disease-causing microbes could potentially trigger autoimmune diseases like Crohn’s disease in those who are susceptible because their finely tuned immune balance is somehow off. Maybe that’s why bakers have the highest Crohn’s disease mortality and, from a different data set, also have among the highest rates of Crohn’s disease, as you can see at 0:30 in my video Is Nutritional Yeast Healthy for Everyone? Perhaps a “hypersensitivity to baker’s yeast…may play a role in Crohn’s disease.”

If you take people with Crohn’s and remove from their diets the three foods to which they appear to have the most antibodies, in order to try to calm their disease, and then add those foods back, you can provoke the symptoms once again and re-stimulate the inflammation. So, for example, an anal fistula gets nice and dry off those foods, starts oozing again once the foods are back in the diet, and then the spigot’s turned back off when the foods are removed once more, as you can see (ew!) at 0:57 in my video.

However, without a control group, you can’t exclude the possibility of a powerful placebo effect. There hadn’t been any such randomized controlled trials until researchers came up with a brilliant design. They tested people with Crohn’s for antibodies to 16 different foods and then randomized the subjects into two groups. Both groups were told to avoid four foods, but one group was told to avoid the four foods they reacted most to, while the other group was told to avoid the foods they reacted least to. The group assignments were given in sealed envelopes, so no one knew who was in which group until the end. So, did it matter? Yes, more than twice the probability of major clinical improvement was seen in the group told to stay away from the four foods their blood reacted most to—but that wasn’t just yeast. In fact, the “exclusion of milk, pork, beef, and egg was most strongly associated with improvement,” leading the researchers to suggest that perhaps instead of doing fancy blood tests, we should just tell our patients to cut out meat and eggs and see how they do. This would be consistent with population studies that associate “diets high in animal fat” with an increased risk of inflammatory bowel diseases, as well as interventional studies showing that a plant-based diet, in which meat is cut down to about one serving every two weeks, can drop relapse rates as low as an extraordinary 8 percent over two years.

But, what about the whole yeast question? Can’t you just put some yeast up someone’s butt and see what happens? Why, yes! Yes, you can, and researchers have. Indeed, researchers tested rectal exposure to six different foods, including yeast, in Crohn’s disease patients. This was kind of like a skin prick test, but instead of pricking the skin, they pricked the inside of people’s rectums with various foods. You can see at 3:00 in my video the various prick sites for the different foods, and it’s clear that yeast gave the most significant reaction in Crohn’s patients.

It appears that baker’s yeast, which is the same yeast as brewer’s yeast and nutritional yeast, may indeed have disease-causing importance in Crohn’s disease, but the good news would then be that it “may be of therapeutic relevance.” If Crohn’s patients went on a yeast-free diet, would they feel better? You don’t know until you put it to the test.

In fact, that’s exactly what the original study linking yeast and Crohn’s disease suggested back in 1988. “A controlled trial of a yeast free diet for patients with Crohn’s disease may therefore be worth while.” Why did it take years before such a study was done? Well, who’s going to fund it? Big Soda Bread? Thankfully, there are charities like the National Association for Colitis and Crohn’s disease, willing to put up the (yeast-free) dough.

Nineteen patients with Crohn’s disease ate their regular diet for a month and were then switched to a yeast-exclusion diet. There was a significantly higher CDAI, Crohn’s Disease Activity Index, which assesses symptoms like abdominal pain and diarrhea, during the period when they were eating yeast, compared to the yeast-free period. So, there was worse disease activity with yeast than without. Okay, but what was this yeast-free diet? They didn’t just cut out bread and beer. The researchers switched people from dairy milk to soy milk and from white flour to whole wheat, for example. Just cutting out milk can sometimes help with inflammatory bowel disease, as you can see at 4:43 in my video.

So, with so many dietary changes, how do we know what role the yeast played? This is how we know what role the yeast played: After placing the subjects on the new yeast-free diet, they then challenged the Crohn’s sufferers with either a capsule of yeast or a placebo. A tiny amount of yeast, like giving them a quarter teaspoon of nutritional yeast a day, made them worse, suggesting “yeast may be important in the pathogenesis [disease process] of Crohn’s disease.”

Now, for the vast majority of people, yeast is not a problem, but in susceptible individuals, it may trigger an abnormal immune response in the gut. But, wait. I thought the paratuberculosis bug was considered a trigger for Crohn’s disease. Well, maybe infection with paraTB is what “induces a hypersensitivity response to dietary yeast.” Who knows? The bottom line is that people with Crohn’s disease should not go out of their way to add baker’s, brewer’s, or nutritional yeast to their diets.

I introduced this topic in Does Nutritional Yeast Trigger Crohn’s Disease?, then took a bit of a tangent with Is Candida Syndrome Real?. Next, I finish up this video series by talking about another autoimmune disease that appears to be affected: Dietary Cure for Hidradenitis Suppurativa.


For more on Crohn’s, see Preventing Crohn’s Disease with Diet and Dietary Treatment of Crohn’s Disease

And paratubercuwhat? See Does Paratuberculosis in Milk Trigger Type 1 Diabetes? and Does Paratuberculosis in Meat Trigger Type 1 Diabetes?

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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:

Supplement Labeling Fraud is Widespread

The regulation of dietary supplements in the United States has been described as “too little, too late.” “Dietary supplements may be adulterated with dangerous compounds, be contaminated, fail to contain the purported active ingredient, or contain unknown doses of the ingredients stated on the label; be sold at toxic dosages; or produce harmful effects” in other ways. As I discuss in my video Black Raspberry Supplements Put to the Test, “[i]f the composition and quality of ingredients cannot be reliably ensured, the validity of research on dietary supplements is questionable. Moreover, the health of the US public is put at risk.”

A private, third-party company that has independently tested thousands of supplements “identifies approximately 1 in 4 with a quality problem” because it either does not contain what it says it contains, is “of substandard quality,” or is contaminated in some way.

Let’s look at an example. I’ve produced a few videos on the remarkable properties of black raspberries, including one on oral cancer. These berries can’t always be found fresh or frozen, so how about black raspberry supplements, which are available in stores and online? At 0:56 in my video, I show a bottle of Pure Black Raspberry by Pure Health, that says “Fresh – Raw – Pure” right on the label. Sounds good, don’t you think? When we look at the back of the bottle, the label says it contains only seedless black raspberry powder “and absolutely nothing else!” It’s nice to see there are no fillers or artificial ingredients, so why not plunk down $23.77 for a bottle? Well, it turns out we’ve been had.

The first clue is that the image on the front of the label is actually blackberries that had been Photoshopped to look like black raspberries. Pure Health couldn’t even be bothered to put a real image on its fake supplement! The second clue is that the “[d]ark olive-brown-black powder in [the] capsule did not look like berry powder and had a medicinal odor,” according to the researchers. So, it was put it to the test, and, indeed, there was no black raspberry at all. Instead of promoting the fact that the Pure Black Raspberry contains only seedless black raspberry powder “and absolutely nothing else,” the company should have just listed that the bottle contains “absolutely nothing” period—or, at least we hope it contains nothing. Who knows what’s actually in the capsules!

The researchers tested every black raspberry product they could find, and, even of the ones with the correct picture on the front and with powder that actually looked like it came from real black raspberries, more than a third appeared to have no black raspberry fruit at all. “At the moment, a consumer who assumes the US dietary supplement marketplace is free from risk”—or is even honest—“is unfortunately naive.”

How widespread is this deception? Researchers used DNA fingerprinting techniques to test the authenticity of 44 herbal supplements from a dozen different companies. As you can see at 2:33 in my video, less than half of the supplements were authentic and actually contained what they said they did. Most contained plants not listed on the label and product substitution, and many “contained contaminants and or fillers,” also not listed on the label. This isn’t just fraud: Some of this deception could really hurt people. For example, one St. John’s wort supplement contained no St. John’s wort at all. Instead, it was actually senna, which is an herbal laxative that “can cause adverse effects such as chronic diarrhea, cathartic colon, liver damage, abdominal pain, epidermal [skin] breakdown and blistering.” In the video at 3:09, you can see how the 12 companies did. Tested products from only 2 of the 12 companies appeared to be completely authentic, with the remaining 10 companies’ products containing filler, product substitution, and/or contaminents. Herbs only work if they’re actually present. Indeed, this study found that 80 percent of the manufacturers in the supplement “industry suffer[] from unethical activities…”.

“Until US dietary supplement products are better regulated and quality control standards for safety, purity, and dosage are defined and endorsed, the safer source for dietary phenolics,” or phytonutrients, “as a consumer is from food intake.”


For more on supplement company shenanigans, see:

What’s so special about black raspberries? Reversal of cancer progression, for starters! See Black Raspberries vs. Oral Cancer and Best Fruits for Cancer Prevention.

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: