What's the story with food intolerances?

1 in 5 people experience food intolerances, a figure that is growing each year. As a result, people are eating increasingly restrictive diets. Unfortunately as they remove some foods, they add highly processed foods in their places, damaging their gut microbiomes and leading to long term health problems.

In this podcast, Jonathan speaks to Dr. Will Bulsiewicz — board certified gastroenterologist, New York Times best-selling author, and U.S. Medical Officer for ZOE — whose latest book is all about food intolerance.

If you want to uncover the right foods for your body, head to joinzoe.com/podcast and get 10% off your personalized nutrition program.


Jonathan Wolf: [00:00:00] Welcome to ZOE Science and Nutrition, where world-leading scientists explain how their research can improve your health.

Today, one in five people suffer from food intolerances, a figure that is growing each year. As a result, people are eating evermore restricted diets, removing dairy, gluten, and many other foods from their plates. Unfortunately, as they remove these foods, they add highly processed foods in that place, damaging the gut microbiome and leading to long-term health problems.

And despite all this hard work, many people see very limited improvements in their symptoms. This whole topic of allergies and intolerance is full of pseudoscience, dubious blood tests, and miracle cures. However, in the last few years, we've seen a revolution in our understanding of gut bacteria - now the stars of the show. This has profound implications for how we should treat our food intolerances. [00:01:00] 

Today we'll focus on what the latest science says, and we're in great company. To answer all your questions, I'm joined by my good friend, Will Bulsiewicz, board-certified gastroenterologist, New York Times bestselling author, and ZOE science board member whose latest book, The Fiber Fueled Cookbook, is all about food intolerance.

My own journey to founding ZOE started 25 years ago when I developed food intolerances myself. So I'm particularly excited by today's episode. 

Will, thank you for joining me today. So look, this is a big topic. I thought it'd be fun to start with a round of quick-fire questions. So starter, for one, have food intolerances increased over the last 20 years?

Dr. Will Bulsiewicz: Probably, yes. Food allergies have clearly increased. In fact, they've more than doubled in the last 60 years. Food intolerances? We don't have clear data, but I think the answer is “yes.”

Jonathan Wolf: Do blood or poop tests for food intolerance work?

Dr. Will Bulsiewicz: So far? No. They are available. They'll send it to [00:02:00] your house. You can order it without your doctor, but they have not been clinically validated.

And my experience is that they actually create more confusion. And they're also very expensive. I don't think they're worth it.

Jonathan Wolf: Brilliant. Can people grow out of allergies? 

Dr. Will Bulsiewicz: Yeah, they can grow out of allergies. It's a very well-described thing that can occur. In fact, with specific allergies - eggs, soy - it's actually likely that you will grow out of allergies if you have them as a child.

Jonathan Wolf: Can you reduce your food intolerances?

Dr. Will Bulsiewicz: In the vast majority of cases? Yes. So, there is a ton of hope for the people at home with food intolerances. You can improve this. You can get your life back. 

Jonathan Wolf: That's a wonderful message. And if you do have food intolerances, do you have to eat a restricted diet? 

Dr. Will Bulsiewicz: In the vast majority of cases? No. In fact, you don't want to. Going into a restrictive diet can actually fuel the food resistance or the food intolerance. And if it's a food allergy, then there are ways the food allergy can [00:03:00] be overcome through a process of reintroduction. 

Jonathan Wolf: And last quick-fire question: How important are gut bacteria for food tolerances?

Dr. Will Bulsiewicz: They're extremely important, which is a part of the reason why we have struggled so much to really understand this topic in great detail. It's just recently that we've developed the tools necessary to start to study this and unpack it. And it's going to take us some time to really get a complete, bigger picture of this. But there are some rules that are very clear at this point that we can run through today and give the listeners at home ways to approach this issue that work and that are tried and true. 

Jonathan Wolf: I think that's brilliant. So, Will, let's go into a bit more detail. That was, you know, we’re shooting across lots of topics. Maybe just start with what are food allergies and food intolerance? 

Dr. Will Bulsiewicz: Sure. So it's important to make a distinction between these things because I find that many times we make a mistake where we were almost using these expressions with these terms interchangeably. These are [00:04:00] not interchangeable terms. They shouldn't be used that way. So, food allergies, food intolerances. Now, there is a reason why we make this sort of interchangeable. They both are manifest with symptoms. A person eats food. And then there is a response that their body has, and that response could be many different things. So it could be digestive symptoms like gas, bloating, discomfort, change in bowel habits, like diarrhea or constipation, but it could also go beyond the gut.

It could be with the skin - you could get hives or rash, flushing, swelling. It could be something involving your cardiovascular system. You can get rapid heart rate, low blood pressure, feel lightheaded. So there are a number of different ways that we can manifest symptoms after eating a meal. And the pattern that you will see with food allergies versus food intolerances [00:05:00] is a bit different and so it's worth kind of unpacking a little bit. 

Food allergies are the response of your immune system to a food. It is your immune system that is basically getting activated and going on the attack. And when this happens, it occurs with specific foods. In fact, Jonathan, there are eight specific foods that we know constitute the vast majority of food allergies.

So for people who are interested in the topic of food allergies, let me share with you what those foods are. And if you need to play this back later and write it down on a piece of paper, go ahead and do that. But there are eight specific foods that you need to be aware of that we believe make up 90% or more of food allergies.

Those are eggs, milk-related products, wheat, soy, peanuts, tree nuts, fish [00:06:00], and shellfish. So eggs, milk, wheat, soy, peanuts, tree nuts, fish, and shellfish. These are the eight specific foods that are most likely to cause an allergy. Now, this doesn't mean that these are bad foods or that they're harming us, but these are what we're seeing in 2022 as the most likely foods to -

Jonathan Wolf: -trigger your immune system for this response.

Dr. Will Bulsiewicz: Exactly. So, when you eat those specific foods, you get a response, and the response with a food allergy could be digestive symptoms alone. But most of the time, it's not. Most of the time, it's going to involve other parts of the body, like a rash, hives, swelling, runny nose, or the one that we really worry about as medical doctors is swelling - like swelling of the throat, swelling of the lips. That's very dangerous. 

All right. So a food allergy is a higher level of concern for me as a medical doctor. [00:07:00] And one of the things to bear in mind is the activation of the immune system in a food allergy could be from the most minimal amount of food. This is the reason why, when a person has a severe peanut allergy, they can't even have the peanuts on the airplane at all. The most minimal amount could activate it. It's not even like consuming a large amount. 

Transitioning over to food intolerances. Food intolerances are also symptoms that occur after food, but these are usually digestive symptoms: gas, bloating, abdominal discomfort, nausea, diarrhea, constipation. These are the types of things that we're looking for.

And food intolerances are not the immune system. This has nothing to do with the immune system, which is why we have to create this important separation. This is, if we were to simplify this, this is typically sloppy digestion. Your body is struggling to [00:08:00] process and break down the food that you are consuming.

And there are a number of different foods that we know are classically associated with food intolerances. Perhaps the most common, most well-known, is dairy - milk. Because milk contains a sugar called lactose, and our body needs to break down lactose to properly digest the milk. And if we struggle to do that, which by the way, this is quite common, it's estimated that 75% of people across the globe have this issue, but, um, -

Jonathan Wolf: -75%, that's amazing.

Dr. Will Bulsiewicz: Yeah, but actually, the population that has this the least are Northern Europeans. But, you know, lactose really exemplifies what a food intolerance is. This is not your immune system getting activated. This is different than a milk allergy. This is a case where you consume a glass of milk and you struggle to process it.

And then, as a result, you end up having cramps and [00:09:00] bloating, and then you get diarrhea. And this is what people experience. Now what's important about food intolerances compared to food allergies is that this is a threshold event. What I mean by that is there's a certain amount that you're capable of tolerating.

Take the person with the most severe lactose intolerance on the planet. I can put two drops of milk on their tongue and they will not get diarrhea. But if they have an allergy to milk, two drops on the tongue are certainly enough to activate the immune system and cause a problem. 

Jonathan Wolf: Got it. So this is an amazing difference in terms of scale you're talking about between this sort of allergy and intolerance then.

Dr. Will Bulsiewicz: A hundred percent - and the amount that you are capable of tolerating is very personal, and it's also a moving target. So the amount that you can tolerate today may be a certain amount, and then tomorrow it may be slightly different. To me, a person [00:10:00] doesn't have a food intolerance when they drink a gallon of milk and then get diarrhea. That would happen to any of us. But when a person is consuming a normal amount of dairy, like a glass of milk, and then they manifest symptoms as a result of that, that's what a food intolerance is. But if hypothetically you were to reduce that amount of milk, cut it down to a quarter of a glass, they may be able to tolerate that. There's a certain amount that they would be able to tolerate. 

Jonathan Wolf: I think we all have the impression that there's a lot more food intolerance now than there was.

It's certainly something that people talk about a lot more. Why are people developing these food intolerances. What's going on? Is there a link with our gut bacteria? You talked about that before. Is there more now than in the past? Having distinguished now the intolerances against these very serious allergies, what's going on with this, um, apparent rise in intolerances?

Dr. Will Bulsiewicz: To comment quickly, [00:11:00] Jonathan, on food allergies and it's important cause I'm going to shift gears back to food intolerances in a moment. It's actually very well described that food allergies are on the rise, and it's quite clear if we went back to 1960, about 3% of Americans had food allergies at that time and fast forward to 2018 and we're up to 7%.

So we have more than doubled in less than 60 years. And the rise of food allergies is in parallel to other allergic and immune-mediated diseases. So we're seeing more celiac disease, more asthma, more Crohn's disease, ulcerative colitis, and we could go down the line, rheumatoid arthritis, lupus, we can keep going.

There are conditions. A quick example is eosinophilic esophogitis. Jonathan, when you and I were children, this condition literally didn't exist. There was no name for this. It was in the late eighties that they started to [00:12:00] identify this pattern. And this is, by the way, an allergic condition seen in both children and adults, where food is causing the immune system to get activated in the esophagus.And it's quite common. I actually take care of it all the time as a gastroenterologist. So when it comes to allergies, our immune system is cruelly more confused in 2022 than it was 50, 60 years ago, and something is going on there. 

Jonathan Wolf: That's the way to understand this, is it? Basically, it's confused because it's attacking food as if it's some sort of pathogen, some sort of illness or something when clearly it should be perfectly happy for you to be eating the eggs or the fish.

I mean, is that the way we should be understanding this? 

Dr. Will Bulsiewicz: Yeah, and, just to define the term a little more, an allergy is a response of your immune system to something outside of your body. So it's not just food. In fact, the most common allergy that people have is allergic rhinitis, where, like seasonal allergies, you get exposed to pollen or dander, and you get a runny nose.

Jonathan Wolf: I know all about that, yep.

Dr. Will Bulsiewicz: So asthma is an allergy, [00:13:00] um, a reactive airway disease, asthma is an allergic disease. And so those are more common, but on the flip side, you can also have a response to food. So that's what we're talking about here today. 

Jonathan Wolf: And Will, you've talked a lot about allergies. I think it's really fantastic to understand that distinction between the sort of stuff that's coming from the immune system and intolerances.

If we sort of switch over to intolerances, which I think for a lot of our listeners is what they're living with, right? Does exactly the same hold that you've described about where you think this comes from and why we've seen the rise?

Dr. Will Bulsiewicz: Yeah, I think so, because I think that one of the critical parts of our gut microbiome that we're just starting to get a better understanding of, is that they're capable of producing digestive enzymes that we are not and they're also capable of supplementing what we are able to do in terms of our digestion. They're able to supplement and provide even more in terms of our capabilities to process and digest our food. So, you know, as a quick example, the [00:14:00] most well-studied of these sorts of phenomenon is lactose.

So I keep coming back to lactose because this is where we have the most research and the picture is most clear. And what we discovered, Jonathan, is that our microbes produce the enzyme that break down milk. So whatever milk you do not personally digest and process with your enzymes, which by the way, are in the lining of your small intestine, if you don't have an adequate amount of enzymes, ultimately the milk will get all the way down to your gut microbes and they will process and digest it. And there are ways in which you can actually train those microbes to become more capable of performing this job for us to the point that you can take a person who has lactose intolerance and you can train these microbes up so that that person who has lactose intolerance will actually be able to tolerate that food [00:15:00] and tolerate it in even larger quantities, in many cases, amounts that they didn't think was possible. 

Jonathan Wolf: And I guess that's sort of analogy a bit with like going to the gym or something, right? If you don't exercise at all and you do something hard, you're likely to injure yourself. It's going to be really difficult. If you are good enough at going to the gym, which none of us do as often as we should, then you're just in much better shape, right, to deal with what gets thrown at you. And is that a sort of analogy to what you're describing, Will?

Dr. Will Bulsiewicz: A hundred percent. That's the exact analogy that I love to use when it comes to this topic because I think it makes it very understandable for people. It’s January 1st, right? You've made your new year's resolution. You're heading into the gym. You haven't been working out. And you start smashing the weights, and you go and you try to run a 10K like on your first day, you're going to be very sore.

Jonathan Wolf: You're in trouble. 

Dr. Will Bulsiewicz: And there's a real chance that you could hurt yourself by pushing yourself too hard. And we know not to do that. So on the flip side, when we introduce [00:16:00] exercise and we start at a lower threshold, a certain amount that we are actually capable of tolerating…And that's a personal thing, right? So I'm a 6’4”, 205-pound guy. So for me, I can lift more weight in the gym than my wife can lift, for example. But on the flip side, if go out for a run, my wife is burning me, you know, and I'm dragging behind. And so we have each individually strengths and weaknesses that are individualized and very personal. 

Jonathan Wolf: I'm just on the internet, so I'll pretend I'm six foot four as well. Will, because you know, I'm not standing next to you.

Dr. Will Bulsiewicz: So, uh, this personal nature, you know, this is one of the things that we understand so clearly, with the work that we're doing with ZOE, which is that each one of us is unique and we have a unique gut microbiome, and that microbiome could be a fingerprint, like it's that personal and there's no one on the planet with a gut microbiome exactly like yours, [00:17:00] including your siblings, even if you're a twin. Tim Spector's research has shown us that even twins have a very limited overlap in terms of their gut microbiome. They're actually very much different.

Jonathan Wolf: And so Will, I think our listeners are saying, “Well, that sounds great…I'm actually not even sure if I've got an intolerance, and you just told me that I can't do one of these food sensitivity tests with my blood or whatever cause it doesn't work. How do you figure it out in the first place whether you have an intolerance?”

Dr. Will Bulsiewicz: You go to the gold standard test. So these food sensitivity tests that exist out there…blood tests, antibody tests, poop tests…The problem with them is that they're going to say, “Eat this, not that.” And you're going to say, “Hold on…this food that you're telling me I have a problem with, I can eat it without restriction and have no issue. And this food that you're telling me that I don't have a problem with… like when I eat that, I feel horrible. What are you talking about?” [00:18:00] And it creates confusion. 

What I've observed in my interactions with patients who do this is they try to use the information and implement it. And they either end up on a very restrictive dietary pattern, or they just end up completely confused and frustrated and they throw their hands up and they don't know what to eat anymore.

And you have to understand that these tests, the reason that we know that they don't work, is because we can compare them to the gold standard. And the gold standard is not a blood test or a poop test or a breath test. It is a method, a method of temporary restriction observing how you response to that restriction, paying very close attention to your symptoms, and then re-introducing. And when you do this like a light switch - on, off on, off - each time that you flipped the current like that, is an opportunity for you to see [00:19:00] how does your body feel with this change that you've just made. And so when you have a food intolerance, when you reduce the food intolerance, you notice that your symptoms improve. When you work it back in, you notice that some of those symptoms come back.

Now, Jonathan, it is entry-level information from my perspective, to identify the food that you have a sensitivity or an intolerance to. That is, it's a good place to start. But what's far more important, from my perspective, is not just, “Hey, what is the food?” The question is, “What is the amount?”

Jonathan Wolf: I think the other thing to sort of recognize is this can be quite hard, right?

Like I've done these managed-by-a-nutritionist-exclusion-diet…You take these things out; you sort of re-introduce, and this is quite difficult. So you describe it as definitely the gold standard, being told by many people there is no other test. There's a reason why ZOE doesn't do any tests for allergies because there are no tests for allergies that actually work.[00:20:00] 

But it is also quite hard in part because you have to cut back your diet a lot to do it, but also because it's, you know, by scale it can be quite difficult to understand. You introduce something and actually it seems to be fine. You've got to do something else. So it's not an easy thing. And I think you need support to go through to try and figure it out. What are your thoughts on that, Will?

Dr. Will Bulsiewicz: There is no question that you need support. There is no question. This is not intended to be done based upon something that you read on the internet. Um, you know, I think that, uh, probably the best way to go about this is to work with a registered dietician who is facile in these particular topics.

And it is important to understand, though, that there is a methodology that exists that allows us to accomplish this. And it can be very overwhelming to try to understand and unpack this without being formally trained in it yourself. But on the flip side, there are resources that exist designed specifically to address these issues.[00:21:00] 

One is to work with a registered dietician who's facile on these particular topcs. But we're going to perhaps talk about this a little bit more at the end, Jonathan, but this is also what my new book was designed to do…was to make this accessible for people, make it easy and effectively, to hold their hands and walk them through the process. Not only so that they can do it, but also so they can understand why they’re doing it. 

Jonathan Wolf: So let's say you've done this and for some people it might be quite straightforward, right? It may really be like, “I'm trying to figure out whether or not I've got lactose intolerance.” And so that's a very specific thing. Let's say we've done this, or I've been through a process and figured out, “Yeah, I really do have some particular intolerances.” And we've learned that it's not just, as you said, “an on/off switch,” but you know, I need to eat quite a lot of this cauliflower and it's causing these problems. Let's come back, I think, to some of the positivity, cause this can be a bit depressing, right? Let's talk about, can we fix this? Can we improve our response? Do I have to cut out all of these things forever? Or can I fix it? And if so, what are [00:22:00] the steps to try and make this better? 

Dr. Will Bulsiewicz: Yeah, you can almost always fix this issue. I give that caveat, “almost always,” because as a medical doctor, I have to leave open this window of possibility that you could have a genetic condition that is less likely, but that could potentially affect your ability.

You know, if you have a genetic condition holding you back, that's a different story. But the vast, vast, vast majority of the people who suffer from these food intolerances, the reason why is not genetic. The reason why has to do with an alteration or disturbance of the gut microbiome and perhaps some other associated factors.

Can you heal? Can you improve? In that setting? 100%. There is no question in my mind. One of the most important points that I want to get across to the people who are listening today is that the solution is not actually through dietary restriction. It may seem like that's the most intuitive [00:23:00] choice. 

Jonathan Wolf: I was gonna say, that sounds very counter-intuitive, right?

You've just basically explained at great length that you're intolerant to some specific things. I think, you know, if I was allergic to something, I would definitely stop it. And you know, my son can't take nuts to school anymore because of this risk to other people. So why are you saying something that sounds like, you know, frankly, it sounds a bit silly, Will. Why don't you just restrict those things?

Dr. Will Bulsiewicz: As you know, Jonathan, many times, the reason that we do clinical research is that the ideas that we have that seem like they make complete sense to us, and they're very intuitive, actually prove to be wrong. 

Quick example: We've been talking about food allergies in children, right? So what is the right way for us to handle pregnancy and early life for a child to reduce their likelihood of developing a food allergy? And, for the longest time, through the time that you and I were [00:24:00] kids, through the time that I have my own kids, the answer to this question was avoidance…restriction. Not only during pregnancy, but also with the child. Don't give them peanuts. 

And they have since done a number of clinical trials to actually answer with great clarity this question. And what they've discovered is that when mom restricts her diet during pregnancy, she increases the likelihood of her child having food allergies. When you restrict the diet of the child, you increase the likelihood of having food allergies. When you introduce the food early, meaning four to six months, you decrease the likelihood of that child having food allergies. They have the exposure that they need. So sometimes the counter-intuitive approach proves to be the truth.

Jonathan Wolf: And so just to make sure that's really clear cause actually, we had a lot of members asking exactly that question, Will, on this topic [00:25:00] about what can parents do to prevent allergies in the children. What you're saying is actually you want to make sure, I guess, particularly those eight products that we're talking about, you know, assuming that you eat them at all, you actually want to expose yourself to them when pregnant and in early childhood. Is that the latest advice?

Dr. Will Bulsiewicz: The latest advice is that a restrictive diet during pregnancy actually increases the likelihood of food allergies in your child. So you actually want to continue to consume those foods during pregnancy. You don't want to avoid those foods during pregnancy. And then the latest advice is that early in life, four to six months, you want to start to introduce these foods along with other foods. It's not that you're going to make peanuts the first food that you hand to your child. 

Jonathan Wolf: And so there's a couple of topics I do want to make sure that we cover before we run out of time, that are related to that that have come up a lot in the questions. One is around FODMAP and the other one is about histamines.

How do they fit into this story you're describing of effectively exercising this muscle of starting to increase your exposure - step by step - against these foods?

Dr. Will Bulsiewicz: Everything that I've said so [00:26:00] far, when it relates to FODMAPs, fits very nicely, very easily, because we've been talking about lactose. Guess what? Lactose is a FODMAP. Some people have raised concerns about gluten intolerance, right? Gluten in wheat products and their fear that this causes symptoms. It's interesting, Jonathan. Our research shows that it's not actually the gluten causing the problem.

Jonathan Wolf: Unpack for us what a FODMAP is. 

Dr. Will Bulsiewicz: Yeah. FODMAPs. It's an acronym.

And really what it's referring to is the fermentable carbohydrates that are a normal part of healthy, natural foods - foods that you want to have in your diet. FODMAP stands for fermentable, oligosaccharides, disaccharides, monosaccharides, and polyols. Basically, what we're doing is we're describing different classes or different families of either sugars, or like, you take a whole bunch of sugars, and you connect them together, and you make something that's more complicated that [00:27:00] starts to transform into something that's becoming like fiber almost. And, um, these are normal, healthy parts of our food. By the way, most FODMAPs are prebiotic. 

Jonathan Wolf: Yeah. I mean, a lot of this stuff is actually the food that our microbes most like, right?

That's the challenge around this and there is some great science that I think was originally discovered in Australia. Is that right, Will? 

Dr. Will Bulsiewicz: Monash University. Monash University was the one to bring forward the FODMAP. And by the way, uh, for those who are really interested in the FODMAP topic, they have an app that's fantastic for those who are interested in diving deeper into FODMAPs. 

But examples of FODMAPs: So lactose from dairy is one. In wheat, barley, and rye, you will find what are called fructans. And they're almost like fiber. And these fructans are what appear to be causing symptoms and people that think that they have gluten intolerance. It's not actually truly a gluten intolerance. It's a fructan intolerance. It's a FODMAP issue. 

Jonathan Wolf: Got it. [00:28:00] So most people who think that they have this gluten intolerance are actually having this intolerance to something else. It's fructans. Is that what you're saying, Will?

Dr. Will Bulsiewicz: Yeah, because gluten’s not the only thing in wheat. Wheat contains many different things and- 

Jonathan Wolf: - enormous complexity, like all foods.

Dr. Will Bulsiewicz: Right. And we blame the gluten just because it's wheat. But it's not necessarily the gluten. And this is actually…you know, there's actually research that makes this very clear where what they've done, Jonathan. They’ve introduced gluten and fructans and they put it into like sort of a breakfast bar where you can't tell what you're eating. You're just eating your breakfast. And they've looked to see what kind of symptoms people have and what they found is that the gluten was not causing symptoms, but the fructans, which you will also find in wheat, were causing the symptoms. That was the issue. 

Jonathan Wolf: So you're not saying to people, “Hey, you have no intolerances.” You're just saying, “Actually the diagnosis that you're making is may be wrong. Is that right, Will?”

Dr. Will Bulsiewicz: I think it's an important distinction because at the end of the day, as a medical doctor, my ability [00:29:00] to improve the life of my patient and to heal my patient begins first and foremost with my understanding of what's happening with their body.

And that's equally true for the people who are listening to us today. If you believe that gluten is the problem, but it's not actually the gluten; it's this other thing that you will also find in wheat, the fructans, then it's important for you to understand that because accuracy, in terms of the diagnosis, leads to your ability to ultimately heal and improve your life.

And many of these people who have gluten intolerance, assuming you do not have celiac disease – which is an important question…you need to be tested for that – but assuming you do not have celiac disease, then actually gluten intolerance can be healed. It can be improved.

Jonathan Wolf: And there is a clear medical test for celiacs, isn't there, Will? 

Dr. Will Bulsiewicz: There's a clear medical test for celiac disease. In fact, there are two specific tests that I would recommend. It's not the blood test. The blood test, I have found, that it is not adequately accurate to diagnose celiac disease. So the two ways that you can [00:30:00] do this is either through doing an upper endoscopy with biopsies of the small intestine. It requires a person to be consuming gluten for at least two weeks leading up to this procedure.

Or, alternatively, you can also start with a genetic test and see the genetic test. It's actually pretty common to have the gene for celiac disease. About one in three people in the United States have it and it's very similar in the UK. But if you, hypothetically, do not have that gene, then you do not have celiac disease. And we know that. 

Jonathan Wolf: That's really interesting. So coming back around to the FODMAPs, cause I think you're quite ready to begin talking about some of these really serious bowel diseases that you can have. It sounds like FODMAP can work. And then I guess the question is: Can you also tolerate these FODMAPs in the same way you were describing everything else?

Dr. Will Bulsiewicz: Yeah, exactly. Well, lactose gives us an example because lactose is a FODMAP and what we've demonstrated is two things: Number one is when you introduce [00:31:00] lactose low and slow, and you allow your body to accommodate and adapt over the course of time, you can actually increase the amount of milk that you drink, Now, whether or not you drink milk is a totally separate question. I personally don't and that's up to you whether or not you want to. But, the point that I'm trying to make is that it's very clear that you have the ability to start low and go slow in terms of introducing the milk. And over the course of time, you can actually adapt and accommodate to this. The other important point is that we have shown through this research that if you heal the gut, you have the ability to improve your digestive capacity. 

Jonathan Wolf: All right. It's amazing. I want to make sure we catch the other question that we had come up so much on social media, which is around histamine intolerance, which is not something you've talked about today. Can you explain what that is? And is there anything you can do about it? 

Dr. Will Bulsiewicz: So, first of all, the good news is there's plenty that you can do about this. This is not something that is locked in that you have to deal with for the [00:32:00] rest of your life. Just like with FODMAPs, you have the ability to heal and improve this issue. Histamine intolerance is a bit complicated.

Uh, Jonathan, we have struggled as a group of clinical investigators to really dig into this topic because there is no blood test to prove that someone has histamine intolerance. The only way to reliably show this is to reduce your histamine intake through your diet and show that you improve. Now, what is histamine?

Let me take it from the top. Histamine is actually a normal, healthy part of our body. It's involved in many different physiologic mechanisms, things that our body is doing like literally right now as you and I are talking to one another, I have histamine, you have histamine, so does the person who's listening at home. We all have it. 

But just like anything else, when you get things out of balance, [00:33:00] when you have an excess of something relative to the way that your body is supposed to be, it could potentially cause a disturbance. And so these receptors that exist throughout our body, when we have an excess of histamine, can become activated. And as a result of that, we get symptoms. And those could be digestive symptoms. Now let me start here: If you have bloating, you need to be paying attention to what I'm talking about right now because the number one symptom in all of histamine intolerance is bloating. All right. That is the number one symptom.

It could be other digestive symptoms as well: discomfort, cramps, diarrhea, constipation, nausea. But histamine intolerance can almost present as a food allergy in the ways that it can affect the rest of your body. So you can have a runny nose after a meal. You could have flushing. Some people get hives. Some people get a rapid heart rate.[00:34:00] 

All right. So these are some of the symptoms. Now, how do we separate histamine intolerance from a food allergy? Well, going back to food allergies once again, they are reproducible and they are specific foods. It's a peanut. It's an egg. It's milk. Whereas histamine intolerance is not necessarily one specific food or class of foods. It's, instead, the foods that are high in histamine. Now histamine becomes a part of our food supply because of the microbes, actually. Microbes are everywhere. They're everywhere. Things are not sterile unless humans make them sterile. So our food is on a natural life cycle. Take the spinach, for example. The spinach, you know, starts off as a seed, grows into a leaf, and you pluck that spinach, and you could consume it. But if you don't consume it, it starts to eventually wither up and then it will brown.

[00:35:00] And then basically it wants to turn into soil, right? It wants to be degraded. And the microbes are responsible for every single part of what I just described – all the way from the seed, all the way down to the decomposition and the earth taking it back. And in this process for all foods, there is this window where we have the opportunity - it's the perfect time for us to eat this food. It's not a seed. You're not going to eat that. Or, in some cases, you do, but with the spinach you’re not. And it's not the decomposed brown stuff. So in this process of the life cycle of our food, the microbes are in play. They're actively at work on this food. And one of the things that they will do is they will produce histamine. They produce this from an amino acid called histidine. And there are these interesting stories, Jonathan, about people eating fish and getting histamine overload, histamine toxicity. 

[00:36:00] Fish is one of the most common sources of histamine intolerance. If you took that fish and you caught it, and you took it home and you ate it, you wouldn't have an issue. But because the fish is caught and then it goes through a series of days to weeks prior to consumption. You are giving the microbes an opportunity to basically do their thing and transform histidine into histamine. And the food then becomes high in histamine. 

So what are histamine rich foods that people should be aware of? The classics are the fermented foods. So not just fermented foods, but also foods like alcohol. Guess what? Alcohol is a fermented food. Vinegar is a fermented food. These types of things can be disruptive to someone who has histamine intolerance and they will notice that they get symptoms with these particular foods. 

When it comes to plants - so I mentioned like fish, shellfish, um, actually most animal [00:37:00] products potentially are at risk for this happening - and when it comes to plants, there's sort of four classics that people need to know: spinach, eggplant, tomatoes, and it breaks my heart to say this, but avocados. Cause I love avocados. So spinach, eggplants, tomatoes, and avocados.

Now, like again, if you picked that spinach leaf out of your garden and you ate it, you would be fine. But because the spinach sits in a container in your store for a period of time, by the time it actually gets to you, it's high in histamine. So now with histamine intolerance, again, we reduce our histamine intake through our diet.

We observe how we feel, and that will allow us to identify whether or not we have histamine intolerance. And one of the important things that just want to point out - it's a complex issue, we could do a whole podcast on this, Jonathan - but one of the things that I [00:38:00] want to point out is that there are ways in which once you know, once you know that this is an issue for you, you are in a position of power because you now understand your diagnosis, which you didn't before. 

And there are ways in which you can approach this issue to improve your histamine intolerance. Number one, you can heal your gut. It's very clear that histamine intolerance also involves damage to the gut microbiome. So you can heal your gut and improve your capacity and ability to process and digest histamine.

Number two, there's a very interesting hack, a health hack, that you can do at home. There's an enzyme that breaks down histamine. It's a part of our body. It's in there right now. It's called D A O - diamine oxidase. All right. So, a person who has histamine intolerance may have inadequate levels of [00:39:00] DAO. Now you can buy a supplement for DAO and it's crazy expensive, and it actually comes from the kidneys of pigs. You could do that. But the alternative choice, is far more attractive and keeps a lot of money in your pocket, which is that you can sprout legumes, specifically peas. But actually all legumes, when you sprout them, they produce this enzyme - DAO. And when you sprout peas, they will produce this enzyme, and you consume those peas, those sprouted peas, and you are actually supplementing in the exact same way, in fact, an even more powerful way than you would with the pig kidneys. And, one last point on that, Jonathan, real quick, is that when you do sprout these peas, there's something interesting that you can do again, another hack, you can actually put them in the dark. So you cover up the sprouting jar [00:40:00] and you put them in the dark.

What's actually happening there is you're creating stress, and this stress brings out the best in these peas because they actually crank up the DAO that they produce substantially. And this can be beneficial. 

Jonathan Wolf: Wow. Well, uh, well, I think we have a whole podcast just on that. I think that's been a fantastic…I know this is a whistle-stop tour. I know that your latest book goes into a lot more detail on many of these topics. If I was just going to sort of summarize, I guess, the conversation, I guess the first thing is that intolerances are not the same as allergies. No, the allergies are linked to our immune system. I think you said there were eight specific foods that tend to trigger almost all of these. And this is also very separate from, you know, very serious bowel diseases like celiac and things like you've talked about. I guess the next thing is it's now clear that the microbiome, you know, this bacteria in our gut is really central to this whole, um, experience and the good news about that is because that microbiome is itself changeable based upon what we [00:41:00] eat. There's a lot you can do. And so rather than heavily restricting our diets and switching to these highly processed foods, which themselves are going to cause us all of these health issues in the future, actually, you know, the first step I think you've talked about is there's a very well known process to understand what our intolerances are - that there is no magic blood test or anything else, which is going to measure this, which is, you know why ZOE doesn't include an intolerance test because there isn't something like that that exists. And once we've done that, interestingly, the next step is the exact opposite of what you would expect. You know, having figured out that you have these things that you're intolerant to rather than cut them out completely, actually, you sort of start a process where you lower the levels. Still, then actually you're sort of introducing them back in because the objective here is really to heal your guts. And we know that healing your gut is about giving it, above all, lots of these different plants that are going to support the different microbes. And so there's this wonderful story I think you're saying that you can overcome your sensitivities. 

We then talked quite a lot about histamine intolerance and I think the key [00:42:00] takeaway is you need to sprout peas in the dark. So we will definitely share something in the show notes. And Will, I hope you've got a picture of your own, darkly, sprouted peas, because I know that Tim and others will be very competitive there. And I guess just to wrap up, this is an area where the science is continuing to develop fast, right?

Like, and I think one of the reasons that you were excited when we first spoke to you about getting involved in ZOE is this ability to start to collect enough data to really try and understand better the links between sort of individual bacteria and intolerances. And we have to be careful not to oversell how well we all understand this yet because actually this is still a, uh, an emerging field.

Is that fair on that last point, Will? 

Dr. Will Bulsiewicz: I agree with everything that you said in terms of key points. I believe that those are all are excellent. And I think that the bottom line is that we believe that the gut microbiome is at the heart of this. Still, it's a very personalized thing that is likely driving and fueling these symptoms that you're experiencing. And doing population-based studies might not going to be [00:43:00] adequate in terms of unpacking and understanding the complexity of your completely unique gut microbiome.

And so I think where this brings me to is that ultimately we need a company like ZOE, or we need an approach that ZOE takes, that allows us to integrate the information from the individual people with their individual gut microbiome and start to identify these patterns that exist that may be predisposing to their symptoms.

And then once we understand that that's when we can then move into the next phase, which is okay then how do we manipulate this? But for the time being, we do know that this approach that I'm describing (temporary restriction, observing how you feel, and then working the food back in), we do know that this works and we do know that it's possible to heal and improve your gut and overcome these food intolerances.

And so really, truly, it's a story of hope. You can figure out where the problem exists, and you can make it better, and you don't need to continue to suffer from these issues. And that's [00:44:00] what I have spent my career working on, and I took all of these ideas, and I brought it into my newest book, the Fiber Fueled Cookbook, which is really not just a cookbook. I mean, it is, it's 125 recipes, full-color photography, but for me, it’s more of like, I'm giving you a toolkit to improve your gut health. 

Jonathan Wolf: Brilliant. Well, thank you so much for taking the time today. I really enjoyed that, and I look forward to a future podcast talking about other topics around the microbiome. 

Dr. Will Bulsiewicz: My pleasure. Jonathan. Thanks so much. Thanks, everyone for listening. 

Jonathan Wolf: You're welcome. Bye-bye.

Thank you to Will for joining me on ZOE science and nutrition today. We hope you enjoyed the episode. If you did, please be sure to leave us a review and subscribe. If you're interested in learning more about ZOE and the best foods for your body, you can head to joinZOE.com/podcast/ and get 10% off your personalized nutrition program. Finally, if this episode left you with any questions, please contact ZOE on Instagram or Facebook, and we will try [00:45:00] to answer them in a future episode, as always. I'm your host, Jonathan Wolf and ZOE Science and Nutrition is produced by Fascinate Productions with support from Sharon Feder here at ZOE.

See you next time.