The surprising truth about lectins
What are lectins, and are they dangerous?
These “antinutrients” have come under attack and were recently the subject of a dietary fad fueled by a popular book. As always, there’s more to the story.
In today’s episode, Jonathan is joined by Dr. Will Bulsiewicz to dive deep into the world of lectins.
They dissect questionable studies, debunk myths, and offer expert advice about how to approach foods containing these misunderstood compounds.
Will is a board-certified gastroenterologist with 14 years of experience. He’s also the New York Times best-selling author of Fiber Fueled and ZOE’s U.S. medical director.
Follow ZOE on Instagram.
Lectins as bioactive plant proteins: A potential in cancer treatment from Critical Reviews in Food Science and Nutrition
Plant-derived lectins as potential cancer therapeutics and diagnostic tools from BioMed Research International
A legume-based hypocaloric diet reduces proinflammatory status and improves metabolic features in overweight/obese subjects from the European Journal of Nutrition
Intake of legumes and cardiovascular disease: A systematic review and dose-response meta-analysis from Nutrition, Metabolism and Cardiovascular Diseases
Effects of dietary pulse consumption on body weight: a systematic review and meta-analysis of randomized controlled trials from The American Journal of Clinical Nutrition
The "white kidney bean incident" in Japan from Methods in Molecular Biology
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Episode transcripts are available here.
[00:00:00] Jonathan Wolf: Hello, and welcome to ZOE Shorts, the bite-sized podcast where we discuss one topic around science and nutrition. I'm Jonathan Wolf. I'm joined by Dr. Will Bulsiewicz, and today's subject is lectins.
[00:00:15] Will Bulsiewicz: Lectins have been recently under attack, Jonathan, and we’ve seen them become the subject of a dietary fad that was fueled by a popular book. Now, some people will say that lectins are toxic and inflammatory, that they cause weight gain and leaky gut syndrome.
[00:00:28] Jonathan Wolf: Well that sounds pretty scary, Will. What are lectins? And are they safe and are they healthy?
[00:00:35] Will Bulsiewicz: Well that’s what we're going to find out. To start, lectins are a type of antinutrient. These are compounds that make it hard for your body to use other nutrients properly. But, some antinutrients actually have beneficial effects.
[00:00:57] Jonathan Wolf: Okay, that's pretty confusing Will. An antinutrient doesn't sound like anything that I would like to have. And I'm excited to take a closer look at the world of lectins.
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So Will, you said lectins are a type of antinutrient. Now, antinutrients, that sounds a little bit scary to me.
[00:01:45] Will Bulsiewicz: That's completely understandable, Jonathan. But, there's nothing to fear, my friend. We're here to explain all of this.
Antinutrients are compounds that can interfere with your body's ability to use the nutrients that you consume in your diet. And they can come in many forms. They could be drugs, proteins, chemicals in your food. Amazingly, some nutrients can actually act as antinutrients.
[00:02:10] Jonathan Wolf: So Will, I'm just getting more confused. Is this yet another one of these scientific words designed to baffle me and everybody else listening to this?
[00:02:18] Will Bulsiewicz: Well, I think the answer is in the nuance, Jonathan, because although antinutrients can interfere with your body's processing of nutrients, first of all, you're likely to destroy most of them when you cook your food.
And, when they are present, they're usually present in such small quantities that they actually help your body to maintain a nutritional balance. It's like having brakes in your car. You don't want to be all gas all the time. You want the ability to slow things down sometimes.
So don't be put off by the scary name antinutrient. They're actually highly unlikely to harm your health when they're eaten as a part of a normal diet.
[00:02:51] Jonathan Wolf: Well, I'm glad that we've cleared that up. So, you were just explaining that lectins are a type of antinutrient. Can you tell me more about these things?
[00:02:58] Will Bulsiewicz: Yeah, let's dig into lectins a little bit. So, the lectins, these scary things that we've heard about, these are proteins that are known to bind carbohydrates, and you'll find them everywhere in nature.
So, both animals and plants have lectins, and those lectins play a role in their physiology, the way their body works. You'll find them in bacteria, fungi, unicellular organisms, I mean, basically your microbiome. You know, the bottom line, Jonathan, is this. I have lectins, you have lectins, we all have lectins.
[00:03:26] Jonathan Wolf: Well, now I feel glad to be invited to the lectin party. I'm feeling a lot less scared of them now I know I'm full of them. Where else do we find them?
[00:03:35] Will Bulsiewicz: Well, we wouldn't be discussing them if they weren't also in our food, of course. You'll find them disproportionately represented in certain specific food groups.
For example, whole grains, legumes, many fruits, certain nuts and seeds, some dairy products, and then the nightshade vegetables. We've discussed these in a prior podcast episode for those who are interested, but those are tomatoes, potatoes, eggplant, bell peppers, and chili peppers.
[00:03:59] Jonathan Wolf: So hang on a minute, Will, because we started off saying like, our lectins really bad for you.
And now you've listed like this long list of food that sound like basically the list of really healthy foods that everyone's being told they should eat. So why are people suddenly kicking up this big fuss and saying actually lectins might be terrible for us?
[00:04:18] Will Bulsiewicz: This is exactly the point, Jonathan, which is that these healthy foods like beans and whole grains that, I mean, frankly, these have been the staple of the healthiest diets around the world for hundreds of years.
And then here comes this popular claim out of nowhere that these lectins are causing inflammation and weight gain and leaky gut syndrome.
[00:04:38] Jonathan Wolf: So is there much truth to these claims is I guess the obvious question.
[00:04:41] Will Bulsiewicz: Okay, let's get this out of the way because we do need to unpack this. It is true that if lectins are consumed in excessive amounts, like not smally excessive, like massively excessive amounts.
They can cause food poisoning, and there are actually several reports of this happening.
[00:04:58] Jonathan Wolf: I'm glad you mentioned this because actually our team here at ZOE, led by Yella, have done some great research and have managed to pull up a couple of bizarre cases that I have to share. So for example, they unearthed a very unusual event at a British hospital back in the 1980s involving red kidney beans.
Can you tell us a bit more, Will?
[00:05:19] Will Bulsiewicz: This was not a great moment for the NHS, Jonathan.
[00:06:06] Jonathan Wolf: I love Will, that even as a gastroenterologist you are laughing at this story. So that’s good, even you can’t keep a straight face while discussing it.
[00:06:08] Will Bulsiewicz: Well, it’s a bit sensational, Jonathan. I feel like this is something we’d read more likely in a tabloid than a medical journal.
[00:06:10] Jonathan Wolf: I was going to say, I think what I love is because it happened to a whole bunch of doctors, they ended up writing this up in like a medical journal. So I think that’s quite funny.
[00:06:12] Will Bulsiewicz: God forbid a doctor gets sick once in a while, you know?
[00:06:13] Jonathan Wolf: Now this doesn't sound great, and I think our team found another case in Japan involving white kidney beans. Is that right?
[00:06:14] Will Bulsiewicz: Yes, indeed. This is the infamous white kidney bean incident, as it's popularly referred in academic circles. So this was actually much more recently, this was in 2006, and it was brought on by a Japanese television station. And they did something that, I don't really know how else to say this.
It was dumb. What they did was very dumb.
They encouraged their viewers to consume powdered white kidney beans. Okay, so uncooked powdered white kidney beans. Like, like grinding them up in a spice grinder or a coffee grinder. Anyway, the viewers, many of them got sick. And more than a thousand people ended up calling the television station angry and with an upset tummy. So like nausea, vomiting, and diarrhea.
[00:06:55] Jonathan Wolf: Wow, so all these people calling up and saying, I did what you said and now I feel really sick.
[00:06:56] Will Bulsiewicz: Yeah, I’m sure the soundboard was popping off and people certainly were not happy at this moment.
[00:06:58] Jonathan Wolf: So, you know, forgive me, Will, because you were saying, like, I don't really think it's such a big deal, but that sounds pretty bad, both these examples, and I thought you were really trying to defend lectins.
[00:07:08] Will Bulsiewicz: We will get to that, Jonathan, and I understand this does sound slightly scary.
That's understandable, but in both of these cases, there's some things that we need to observe. So, first of all, the beans were not cooked in either case, right? This is inappropriate cooking of the beans, and I don't know about you, Jonathan, but like for me, I tend to prefer my beans cooked. If you've ever tried to chew an uncooked bean…
It's not a good time, and there's a high probability of chipping your teeth or losing a tooth. You know, that's just me, but anyway. It's also really important to acknowledge that this is two case reports from the last 40 years, and nobody became seriously ill. So among these two incidents, like, basically, everyone recovered by the next day, people were expected to come back to work at the hospital the next day.
[00:07:52] Jonathan Wolf: So, I’ll hold my hands up, I am also all about the cooked beans. I sort of figured that this is why we invented fire 100,000 years ago. It was exactly so we can eat a whole bunch of things that, if they were raw, made us sick. That’s definitely what I was brought up to believe in school sort of 40 years ago.
So help me to understand what's happening to these lectins as they start with this sort of, y'know, raw, like let's take a bean as an example, and then they become cooked.
[00:08:01] Will Bulsiewicz: Yeah, this is a really important and fundamental point, which is that simply cooking your beans can dramatically reduce the lectin content of them.
So, basically, cooking deactivates lectins, which is the reason that routine consumption of cooked beans does not cause people to get sick with lectin poisoning. Like, you really don't have to worry about this. So, kidney beans are toxic if you consume them raw, which of course nobody does, but proper cooking neutralizes those lectins, makes the kidney beans or any other type of beans safe to consume.
And not only safe, but, I mean, frankly, like, amazingly beneficial. So, I just, one quick point on this. I just want to add that if you buy canned beans, you notice that those canned beans are rather soft, and that's because they've already been cooked. So there's no need to worry about lectins in canned beans either.
[00:08:45] Jonathan Wolf: It's really interesting, because I mean, I didn't grow up eating a lot of beans. I think in general, I didn't grow up with a very high fiber diet. But we certainly had potatoes, and I was definitely, you know, brought up to understand that you can't eat a raw potato, you need to cook it, and so I guess this is just another example of the way in which cooking really changes sort of the chemical structure of the food, and it can turn something that's not safe for us into something that's safe for us.
Or in some cases you can cook it for so long that you lose a lot of the nutrients and it may not be unsafe, but you're also potentially losing. So the point is, you can't compare raw and cooked always in the same way.
[00:09:23] Will Bulsiewicz: Yeah. That's a really interesting point. Cooking is changing the properties of our food.
It is a form of food processing. It's not ultra processed, but it is a form of food processing, and actually studies have shown, there was a study out of the University of California, San Francisco, that by taking literally the exact same food and cooking it, that it actually can have a differential effect on the microbiome.
[00:09:43] Jonathan Wolf: Amazing. So the message I'm hearing so far is: cook your beans or buy canned beans, which are already being cooked. So that's pretty simple. What other research has been done so far on lectins?
[00:09:56] Will Bulsiewicz: Well, Jonathan as with you know, so many dietary fads or scary stories, it's hard to keep up with the way in which the hype is getting away from us with large scale scientific studies looking at something like a lectin free diet.
[00:10:11] Jonathan Wolf: And I know that, again, the team here at ZOE was looking into some of the research on lectins, and actually most of this has been carried out in test tubes and on rats rather than actually on people.
Is that right, Will?
[00:10:24] Will Bulsiewicz: Yeah, that's exactly correct. And this is a really important point. So when these experiments are being carried out, in essence, what they're doing is they're taking some completely unnatural concentration of these lectins. And you know, this sort of setup can give results that would suggest that lectins cause inflammation or a leaky gut, but there's a few problems that we need to acknowledge.
So first of all, these studies, they don't translate well to humans. I mean, the bottom line is like, we are not test tubes or rats. We're much more complicated than these things. And, you know, the second thing is that for every study that says that lectins are dangerous, there are at least as many studies that say that they're beneficial.
You know, for example, there's numerous studies suggesting that lectins protect us from cancer, or heart disease. These are our top killers. We want to protect ourselves from these, and lectins actually can help.
So, fundamentally, these test tube and animal studies are, they're just not showing us what happens when real people eat real food. Which is what we care about, Jonathan, at ZOE. That we want to understand, like, what happens to me if I eat a high lectin diet or a low lectin diet. That's what we care about.
[00:11:34] Jonathan Wolf: So it sounds like we should sort of park the test tubes and the rats. I was pleased to hear we are not like a rat, I’m finding that very positive. I almost want to get that, as like a little badge or a bumper sticker.
So what do we know about the impact of lectins in the context of, like, real food that actual human beings eat?
[00:11:42] Will Bulsiewicz: If you did that, Jonathan, it would only be you and I and the ZOE listeners, it would be like a special club that understands what that means. I am not a rat.
I mentioned that you'll find a lot of lectins in foods like legumes. This gives me a great opportunity to talk about one of my favorite foods, which are these legumes, and the studies that we have to back them up.
[00:11:51] Jonathan Wolf: So Will, what I love about you is that you could have a favorite legume study, and I guess you wouldn't be on the ZOE podcast if you didn't have a favorite legume study, so tell us about it.
[00:12:02] Will Bulsiewicz: I fully acknowledge that I am a nerd. I have, this is not a mystery or a secret. So we hear from the lectin-phobes that we should avoid legumes because lectins cause things like inflammation and weight gain. So here's what I would propose for a study. This is a randomized controlled trial of a legume-packed diet, like a high legume diet versus a diet with no legumes.
And importantly, the researchers held the number of calories completely constant. So basically what we're looking at here has nothing to do with whether you're eating more calories or less calories. It's purely, are you consuming more legumes or no legumes.
Here's what they saw. And this is, like, amazing and kind of shocking. So on this high legume diet, lots of beans and lentils, they found that the C-reactive protein, which is a marker of inflammation, dropped not by 5% or 10% or even 25%. It dropped by 40%. This is a really big number.
[00:13:19] Jonathan Wolf: 40%?
[00:13:20] Will Bulsiewicz: 40%, dropped their inflammation marker. Simultaneously, their blood pressure and their cholesterol also dropped.
But the most fascinating part I haven't even mentioned yet, which is that the people on the high legume diet lost more weight. And this is despite the fact that they were eating the same number of calories. It is not just calories.
[00:13:22] Jonathan Wolf: So that's amazing. And actually what you're saying is, in this situation, the diet with the higher amount of lectins actually led to lower inflammation. So that's pretty good news, it sounds like, for fans of lectins and fans for, you know, beans and lentils, because I don't think anyone other than scientists talks about legumes that I've ever met.
What else have scientists learnt from the legions of legume research that is going on?
[00:13:47] Will Bulsiewicz: I mean, this is just one study, you know, it may be my favorite study, but there's tons of research on the benefits of legumes in particular. So a notable discovery that's been found is that people who consume more legumes, they can more effectively lose weight. They have better blood sugar control, therefore less likely to be diagnosed with type 2 diabetes. The science also shows a decreased risk of cardiovascular disease and colorectal cancer.
[00:14:13] Jonathan Wolf: So Will, you're making a pretty strong case for legumes. They're sounding pretty good for us. Now there's also a whole lot of lectins in other foods like whole grains, right?
[00:14:22] Will Bulsiewicz: Yeah, we've been focusing on the legumes quite a bit, but this is also important and true. And so let's take a look at whole grains. In one study, they showed that increasing your daily consumption of whole grains by just two pieces of whole grain bread, they actually rewarded those participants with a lower risk of coronary heart disease, lower likelihood of death from cardiovascular disease, lower likelihood of diagnosis of cancer, even a lower likelihood of death from all causes.
Death from respiratory diseases, death from infectious diseases, more likelihood of type 2 diabetes, and more likelihood of death from all non cardiovascular, non-cancer causes, which is a huge category, but also quite important. So I have a message to all the lectin haters. Mic drop. There we go.
[00:15:12] Jonathan Wolf: And that's from eating more whole grain bread, which I would never have put even that high on the list of what you might want to eat. So that is definitely you sort of waving the lectin flag ferociously.
Now the team here at ZOE also looked into some of these studies and it seems that, you know, in general people are going into these consuming, like, really quite small amounts of grains and legumes. So is it possible that actually everyone listening to this in general, they're probably consuming, you know, a lower amount of lectins than maybe they would be if they were in these studies with these health benefits?
[00:15:45] Will Bulsiewicz: That's right, Jonathan. You know, people who are following a ZOE lifestyle, they may be higher in the lectin consumption, but let's take a look at what's really happening out there. One study suggested that 98% of Americans are actually deficient in their whole grain consumption.
Meanwhile, the average American is consuming only 6 pounds or 2.7 kilos of beans per year. So if you get nerdy, which, as I mentioned earlier, I specialize in this, this means that you're consuming only 2 ounces of beans per week. That's nothing. And if we pause for a second, you know, let's just think about this.
The anti-lectin club is claiming that this is the cause of all of our problems. This is the cause of our inflammation and our weight gain and our gut issues. We've already discussed the science doesn't support this. Now I'm showing you the logic doesn't support this either.
[00:16:39] Jonathan Wolf: So that's what the current diet of people in the U.S. is looking like. Is there any research, other than on rats and in test tubes, that suggests that we feel better on a low lectin diet?
[00:16:49] Will Bulsiewicz: We have to understand these are highly exclusionary diets, which actually make it difficult for people to consume enough calories on a daily basis. So the result of this, you know, if you're on a super restricted diet, then people will, in the beginning, lose weight. That's what they seem.
But there's no evidence that this has anything to do with lectins. And as for people who claim significant improvements by reducing lectins, there's a couple things that this could be, and I think they're just kind of like very clear to me.
First, this could be a placebo effect, or it could also be the result of excluding something other than lectins, such as FODMAPs. After all, our food is not just a big bag of lectins, like, it's nutritionally complex. And there can definitely be something else in our food that's causing our symptoms.
[00:17:38] Jonathan Wolf: And I think there's a study that sort of gives us some insight into this around gluten. Is that right, Will?
[00:17:44] Will Bulsiewicz: Yes, exactly, Jonathan. And this is another one of my favorites. So you know, gluten, first of all, most people don't think of gluten as a lectin. It is. This is the most famous of the lectins. It's something, it's a lectin that has a star in the lectin hall of fame.
So consider another randomized control trial in which researchers gave people, the people that they were studying, by the way, they had gluten sensitivity. Okay, these are people who report that they are sensitive to gluten, and they gave them an oatmeal bar that they would consume every day for a week.
[00:18:15] Jonathan Wolf: So just a plain, simple oatmeal bar, or is there some sort of science-y twist here?
[00:18:21] Will Bulsiewicz: Of course there's some sort of science-y twist here. So, concealed within this oatmeal bar, they snuck in, one of three things: gluten, fructans, which I'll explain in a moment, or a placebo, that was sugar. So fructans are short-chain…
[00:18:36] Jonathan Wolf: You gotta watch out for these science-y researchers slipping you oatmeal bars. Clearly, you don't know what they're, like, smuggling in underneath the oats. I love it.
[00:18:44] Will Bulsiewicz: They do sound a little bit sketchy, but thankfully we have institutional review boards to ensure that they do have ethical standards. And, you know, and the study actually serves a really important purpose, which of course all studies should.
So we're trying to understand, like, what is the role of gluten in these people that have gluten sensitivity? Now, I mentioned fructans, which is one of the things that was hidden within these oatmeal bars. Fructans are short-chain carbohydrates that you'll actually find in gluten containing foods like wheat, barley, and rye.
So like wheat, barley, and rye contain both gluten and also fructans. So they're actually a type of FODMAP. And so every person was exposed to a different bar, after taking a break for a week to let his or her symptoms settle down. So basically like everyone is getting a chance with each one of these three bars.
And during the week that they're consuming these bars, they measured digestive symptoms to see, like, how are you feeling? Bloating, gas, abdominal pain, diarrhea, constipation. How are you feeling?
[00:19:44] Jonathan Wolf: So everybody got these three bars, one with just like some sugar in it, one with the gluten, which is this lectin that you're talking about, the super-lectin, and one with the fructans. So what did they find?
[00:19:55] Will Bulsiewicz: Okay, I love this. This is one of my favorite findings in a study. So when you compare to placebo, because of course the placebo is the standard that we're going to compare it to. The patients who were consuming the gluten-containing bar actually had less symptoms.
Let me say that again. They had less symptoms with the gluten-containing bar and more symptoms with a placebo.
[00:20:00] Jonathan Wolf: These were the people who said they had gluten sensitivity?
[00:20:02] Will Bulsiewicz: These are people that have gluten sensitivity and the placebo is causing more symptoms than the gluten. So, like already, this is quite hot.
Now, when they ate the fructan-containing bar, they were triggered and they had a massive increase in their digestive symptoms. There was clearly something going on there. So, in other words, these people who have gluten sensitivity, in this study, it wasn't gluten. They're actually sensitive to fructans. It's a fructan sensitivity, which is a form of a FODMAP intolerance.
[00:20:46] Jonathan Wolf: And so your conclusion there is, actually, the lectins aren't the issue at all for these people, and it's something else completely in this food that was causing the problem.
[00:20:57] Will Bulsiewicz: That's exactly right. So when you eat these foods, wheat, barley, and rye, you get symptoms. You attribute those symptoms to gluten. You say, I have gluten sensitivity, when in fact, we are misattributing the symptoms. It's not the gluten, it is the fructans that also. are in the wheat barley and rye.
[00:21:15] Jonathan Wolf: So Will, when I wrap all of this up together and you've given us a wonderful tour of some quite fun scientific experiments. Despite the strange events of the white kidney bean saga in Japan and the healthy eating day in that hospital in 1988, it seems to me like lectins sound pretty safe, you know, as long as I don't eat my beans uncooked.
Is that the right verdict?
[00:21:39] Will Bulsiewicz: Yeah, I think that you got it right, Jonathan. It's actually that simple, and I get a little bit emotional about this topic and a little worked up about it in case people couldn't tell during our conversation. And that's because it really bothers me because along comes a fad diet that breeds misinformation on the topic of lectins, and it leads to scaremongering, and we're scaring people away from foods that we're already under consuming and that we need more of.
I feel like this is an opportunity to make a public service announcement to say, that we just need to be careful when we hear people making statements like "Everything you thought you knew is wrong" or when we see a person and they may have an MD or a PhD after their name, but they are a lone wolf and they are out there claiming that all the other MDs and PhDs got it wrong and they have discovered the solution that millions of scientists across the planet are missing or overlooking.
The bottom line is this: there is no study on a lectin free diet, because a lectin free diet doesn't exist, we will always have lectins in our diet. That's because they are ubiquitous in nature. We all have lectins.
If you're trying to make an argument that lectins are the cause of our inflammation, our weight gain, our leaky gut, you know, sadly what's happened here is we see that studies are being cherry picked, but the entire weight of the evidence, when we look at the big picture, Jonathan, the bottom line is that the evidence does not support this.
And, as I've pointed out, neither does the logic. This is yet, sadly, another example of where cherry-picked science is bad science, misleading science. Now, we know that these foods, beans, whole grains, and, like, other lectin containing foods, not only are they perfectly safe, they're actually good for you. We don't need less, we need more.
But, at the same time, what we have pointed out is that some people do get symptoms with lectin-containing foods, and it's... likely not to be the lectins. There could be another explanation. It may be something like FODMAPs, which we will certainly discuss in another podcast episode.
[00:23:48] Jonathan Wolf: Will, thank you so much.
I think your position is clear and clearly very strong. You've definitely cleared up a lot of confusion for me and I hope for our listeners. Thank you very much.
[00:23:55] Will Bulsiewicz: That's what I'm here for Jonathan, thank you.
[00:23:59] Jonathan Wolf: If you've listened to this, and you'd like to try ZOE's personalized nutrition program to find out how you could adjust what you eat — and maybe have more of those lectin-containing foods — then you can learn more about it and get 10% off by going to zoe.com/podcast. I'm Jonathan Wolf.
[00:24:15] Will Bulsiewicz: And I'm Will Bulsiewicz.
[00:24:17] Jonathan Wolf: Join us next week for another ZOE Podcast.