ZOE Science & Nutrition - The surprising truth about lectins

Episode Date: November 2, 2023

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.  If you want to uncover the right foods for your body, head to joinzoe.com/podcast and get 10% off your personalized nutrition program. Download our FREE guide — Top 10 Tips to Live Healthier: https://zoe.com/freeguide Follow ZOE on Instagram. Mentioned in today’s episode: 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 Dietary legume consumption reduces risk of colorectal cancer: Evidence from a meta-analysis of cohort studies from Scientific Reports Intake of legumes and cardiovascular disease: A systematic review and dose-response meta-analysis from Nutrition, Metabolism and Cardiovascular Diseases Legume consumption is inversely associated with type 2 diabetes incidence in adults: A prospective assessment from the PREDIMED study from Clinical Nutrition The effects of legume consumption on markers of glycaemic control in individuals with and without diabetes mellitus: A systematic literature review of randomised controlled trials from Nutrients 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 Fructan, rather than gluten, induces symptoms in patients with self-reported non-celiac gluten sensitivity from Gastroenterology Is there a nutrition topic you’d like us to explore? Email us at [e-mail], and we’ll do our best to cover it.  Episode transcripts are available here.

Hello, and welcome to Zoe Shorts, the Bite Size podcast where we discuss one topic around science and nutrition. I'm Jonathan Wolfe, and today I'm joined by Dr. Will Bulsiewicz, and today's subject is lectins. Recently, Jonathan, lectins came under attack. A popular book made many people fearful, and as a result, some people believe that lectins are toxic and inflammatory, causing weight gain and leaky gut syndrome. So that sounds terrifying, Will. So what are lectins and are they dangerous? Or is this another food myth?

Well, this is what we're going to find out, Jonathan. Okay, Will, let's get to it. To start, lectins are a type of anti-nutrient. These are compounds that make it hard for your body to use other nutrients properly. But some anti-nutrients actually have beneficial effects. Okay, that's pretty confusing, Will. An anti-nutrient doesn't sound like anything that I would like to have. That's completely understandable, Jonathan. But there's nothing to fear, my friend. We're here to explain all of this. Anti-nutrients 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 anti-nutrients. 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? Well, I think the answer is in the nuance, Jonathan, because although anti-nutrients 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 anti-nutrient. They're actually highly unlikely to harm your health when they're eaten as a part of a normal diet. Well, I'm glad that we've cleared that up. So you were just explaining that lectins are a type of anti-nutrient. Can you tell me more about these things? 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. Well, now I feel glad to be invited to the lectin party. I'm feeling a lot less scared than now I know I'm full of them. Where else do we find them? 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. So hang on a minute, Will, because we started off saying like, are 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? 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. So is there much truth to these claims is I guess the obvious question. 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 small excessive, like massively excessive amounts, they can cause food poisoning. And there are actually several reports of this happening. 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? This was not a great moment for the NHS, Jonathan. In 1988, a British hospital was having healthy eating day and someone brought to this potluck a special lunch that included undercooked red kidney beans. So one medical journal, this was actually written up, they noted that by three o'clock in the afternoon after this lunch, a surgical assistant vomited in the operating room, which of course is not something we want to happen. And then over the next several hours, the hospital staff were struck by an epidemic of vomiting and diarrhea, basically ripping through the hospital staff, everyone who attended this potluck lunch. Anyway, in case

anyone's having their dinner, I guess I'll just leave it there. So now this doesn't sound great. And I think our team found another case in Japan involving white kidney beans. Is that right? 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 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 causing the television station angry and with an upset tummy. So like nausea, vomiting, and diarrhea. So, you know, forgive me, Will, because you were saying, I don't really think this is such a big deal. But that sounds pretty bad, both these examples. And I thought you were really trying to defend lectins. 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. So help me to understand what's happening to these lectins as they start with this sort of, you know, raw, like let's take a bean as example,

and then they become cooked. 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. 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 and canned beans either. 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 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. 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 at 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. 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? Well, Jonathan, as with 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. 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? 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 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. And 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, Zoe, that we want to understand what happens to me if I eat a high lectin diet or a low lectin diet. That's what we care about. So what do we know about the impact of lectins in the context of real food that

actual human beings eat? 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. 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. I fully acknowledge that I am a nerd. 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. 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 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 information. So that's

pretty good news, it sounds like, for fans of lectins and fans for beans and lentils, because I don't think anyone other than scientists talks about legumes that I've ever met. What else have scientists learned from the legions of legume research that is going on? I mean, this is just one study. 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.

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? 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 by 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, 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, lower likelihood of type 2 diabetes, and lower 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. 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? 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 six pounds or 2.7 kilos of beans per year. So if you get nerdy, which as I mentioned earlier, I specialize in this, 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. So that's what the current diet of people in the US is looking like. Is there any research other than on rats and intestines that suggests that we feel better on a low lectin diet? 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've seen. 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 that are 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. It's nutritionally complex. And there can definitely be something else in our food that's causing our symptoms. And I think there's a study that sort of gives us some insight into this around gluten. Is that right, Will? Yes, exactly, Jonathan. And this is another one of my favorites. So 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 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. 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. So just a plain, simple oatmeal bar, or is there some sort of science-y twist here? 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. You got to watch out for these sciencey researchers slipping you oatmeal bars.

Clearly, you don't know what they're like smuggling in underneath the oats. I love it. 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? 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?

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 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. These are people that have gluten sensitivity and the placebo is causing more symptoms than the gluten. 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. 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. 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. 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? Yeah, I think 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 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. 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. 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, maybe have more of those lectin-containing foods, then you can learn more about it and get 10% off by going to zoe.com slash podcast. I'm Jonathan Wolfe. And I'm Will Balsowitz. Join us next week for another Zoe podcast.