Irritable Bowel Syndrome Podcast

It's Complicated: Food and IBS

Lin Chang, MD; William Chey, MD


April 19, 2023

This transcript has been edited for clarity. For more episodes, download the Medscape app or subscribe to the podcast on Apple Podcasts, Spotify, or your preferred podcast provider.

Lin Chang, MD: Hello, I'm Dr Lin Chang, and welcome to Medscape's InDiscussion series on IBS (irritable bowel syndrome). Today we'll be discussing the role of diet and food with our guest, Dr Bill Chey. Dr Chey is the H. Marvin Pollard Professor of Gastroenterology, chief of the division of gastroenterology and hepatology, and professor of medicine and professor of nutrition sciences at Michigan Medicine. He is a member of the board of trustees at the American College of Gastroenterology and on the board of directors of the Rome Foundation. Dr Chey is an expert in the diagnosis and treatment of IBS and other disorders of gut-brain interaction. More recently, he has spearheaded much of the research in dietary factors and modification in IBS. Welcome to InDiscussion, Bill, it's so great to have you. This is the first time I'm interviewing you, so this is a real treat for me — and especially on this topic, which is of great interest to many people. I want to start our discussion with you telling us how you became interested in IBS.

William Chey, MD: Thanks so much for having me on, Lin. It's wonderful to be on the interviewee side as opposed to interviewer side for once. I'm from Rochester, New York. My father was an academic gastroenterologist. He was chief of gastroenterology at the University of Rochester back in the 1980s. I went to college at the University of Pennsylvania and then went to medical school at Emory University in Atlanta. I did my residency at Emory as well before my gastroenterology (GI) fellowship at University of Michigan. I mention all this because, interestingly, when I was at Emory and working a lot at Grady Memorial Hospital (the big city hospital in Atlanta), I never heard the diagnosis of IBS. I'm not sure whether to say that I'm ashamed or embarrassed to admit that. It was just not the diagnosis that we gave to the patient population that we served. On the other hand, when I got to Michigan, almost immediately people were throwing around the term IBS, which I had no familiarity or experience with at all. The thing that struck me about IBS, as I started to get more familiar with it at Michigan, was how diverse the clinical phenotype was. It was hard for me to understand how patients with diarrhea, constipation, or a mixture all had the same diagnosis, and how few evidence-based diagnostic strategies and treatments there were. That's really what got me interested in this space.

Chang: It's really interesting how there was very little training about IBS. You did go to one of the Centers of Excellence in Michigan, so it's great for people to hear more about IBS. I think people are learning and getting more knowledgeable about IBS. I want to start with the topic of food, because that is your expertise and your passion. Food can be the cause of IBS symptoms, but it can also be the trigger of symptoms. How do you envision the relationship of food to IBS as a cause and as a trigger of symptoms, recognizing this can be different between individuals?

Chey: Food is the most important trigger for IBS symptoms. Every survey that's looked at this issue has shown that. I'll give a little bit of history in terms of how I got interested in food. When I started at University of Michigan, even though, as you say, it was considered to be one of the meccas for IBS back in the early 1990s when I started here, I kept hearing from patients over and over again, "What can I do with my diet to try to address my symptoms given the fact that it's food that triggers my symptoms?" The response that I consistently got from the attendings I worked with was, "Oh, it's all psychological. It's got nothing to do with food. There is no diet that's valuable or useful for treating patients with IBS." That really piqued my interest because that's not what the patients were saying at all. It turns out that food is important in this whole experience. The surveys would suggest that probably upwards of 70%-80% of IBS patients associate their symptoms with food. I always use the term "food's complicated." There are a lot of reasons why food may be responsible for the development of symptoms. We tend to focus on carbohydrates, but proteins and lipids are probably equally important in individual patients.

Chang: I think it's so important to listen to patients, and a lot of what I do in my career and my research is based on what we see in patients. I think you're doing the same thing, which is important. Can you explain the difference between food allergy and food intolerance? This can be confusing to people with respect to their role in IBS. Are there any commercially available tests you would recommend to patients with IBS symptoms?

Chey: It's a complicated question, but it's an important question because patients will oftentimes think that if they have experienced an adverse reaction with eating a food, that it represents a food allergy. Of course, we all know that that isn't the case. Food allergy is an immunologically mediated reaction — typically a reaction to proteins within food. The classic food allergy is mediated through an immunoglobulin E (IgE)-related pathway. What we're coming to learn through a variety of interesting experimental techniques is that there are probably different types of food allergy variants that are not mediated through IgE. Those are the variants that are the subject of a lot of investigative interest currently, whether you're talking about endoscopic techniques like confocal laser endomicroscopy or serological techniques like IgG measurement or leukocyte activation testing (LAT) measurement, there are a variety of different mediator release testing (MRT) like basophil activation testing (BAT). You notice they're all centered on this idea that food leads to this abnormal immunological response, which you could argue may represent an atypical variant to food allergy. Right now, we're at the beginning of this road. I'd love to be able to tell you a test that I think is really evidence based, validated, and reliable, but I'm not sure that test exists currently. There are some tantalizing bits of information for LAT and for IgG-based elimination diet testing. Stay tuned. We clearly need to do larger, methodologically rigorous studies to get an idea about whether these things work. Right now, there's a lot more promise than there is evidence.

Chang: I've seen a fair amount of IBS patients who have said they've had a food allergy test, and they say, "I don't think I'm allergic to those foods that tested positive." Do you find that?

Chey: Yes, because a lot of the food allergy testing is actually IgG-based testing. Right now, there is no validated or most effective best in practice methodology in terms of how to create or validate those tests. In fact, there are a lot of IgG-based tests that are on the market right now, but they're created in different ways and focus on different foods. The bottom line is that all of these tests, although they may have a similar label like IgG-based elimination testing, are not created equally. We really need to apply scientific rigor, so we can decide what not only intuitively makes sense but also what works in clinical practice.

Chang: That's so important. What diets have proven efficacy in IBS? I know you've studied this a lot. Can you explain the mechanisms by which these diets can cause or improve symptoms in IBS?

Chey: Yes, that's a whole lecture. I'll try to explain in a couple sentences because there are some interesting new insights into some of the pathophysiology that listeners may be unaware of. First thing, there is no question that the most evidence-based diet therapy for IBS at the current time is the low-FODMAP diet. FODMAP, of course, is an acronym that stands for fermentable oligo-, di-, monosaccharides, and polyols, which are short-chain sugars that the intestine has a difficult time breaking down and absorbing. For that reason, those sugars are available for fermentation in the colon, largely. That fermentation has been largely thought to drive why FODMAPs cause symptoms in patients with IBS. Fermentation leads to the production of gas and short-chain fatty acids, which can lead to luminal distension. That creates an osmotic load, which you would expect may trigger symptoms in a patient with underlying abnormalities in motility and visceral sensation. That makes sense. There's recent work from the University of Michigan group that suggests that a high-FODMAP diet, which a lot of Americans [eat], leads to dysbiosis dominated by gram-negative bacteria. Those gram-negative bacteria preferentially produce larger amounts of lipopolysaccharide (LPS). LPS can lead to changes in permeability of the gut epithelium, which allows it to cross and interact with the immune system and the enteric nervous system. You can imagine that LPS activating the immune system and the entire nervous system can lead to changes in motility and visceral sensation that would otherwise look like IBS. It may be more complicated than just the fermentation and osmotic load story. In fact, I'm quite convinced at this point that it is more complicated than that. The bottom line is there are other diets that are starting to be recognized as potentially beneficial as well, whether you're talking about common sense recommendations like the National Institute for Health and Care Excellence (NICE) guidelines. We're also starting to study the Mediterranean diet, which is quite different than the low-FODMAP diet. We'll see whether this shakes out in our studies to be beneficial.

Chang: You mentioned earlier that the IBS patient population is a heterogeneous population of different symptoms, and the way patients will respond to certain foods will be different amongst individuals. That's why it's probably hard to have one test for food intolerance. It's also the same thing with diet. At the end of the day, you're really trying to get a more personalized diet, which is what you've always talked about. If you look at the FODMAP diet or even Mediterranean diet, it's going to differ between individuals, don't you think?

Chey: No question. I always feel like the low-FODMAP diet unceremoniously kicked the door open for diet therapies in IBS. If you think about the time before the low-FODMAP diet and even during low-FODMAP diet introduction, pretty much nobody believed that it was real or that it would work. I can't even begin to tell you how much criticism I got when I first started talking about this on a national stage in the United States. I think at this point, everybody believes it. In fact, Lin, you and I talk about this all the time — the low-FODMAP diet is overused at this point, not underused. What worries me is the lack of attention in terms of understanding whether a patient has disordered eating or an eating disorder. This is an important take home for listeners: IBS patients, very understandably, have developed almost a PTSD kind of relationship with food. They eat food, they get symptoms. They don't understand why. They don't necessarily even understand what is causing problems. They start eliminating things from their diet. A study from our group, as well as the King's College group and the Monash University group, has shown that the habitual diets of IBS patients are really a mess. They contain numerous potential deficiencies and are potentially dangerous over the long haul for patients, not to mention the fact that this cycle of thinking that the solution is always restricting more and more foods can become potentially dangerous. Think about this: The last thing you want to do as a doctor is recommend a highly restrictive diet to a patient who's already overrestricting their diet. That's why I say I think we're actually overusing the low-FODMAP diet, not underusing it. I think that in many situations where people are using it, they're not using it properly. They're putting patients on restriction and leaving them on it. They're not providing adequate education or counseling in regard to the three phases of the low-FODMAP diet: restriction, reintroduction, and personalization. We have a lot of room to grow and improve, even though diet therapy is on everybody's radar screen at this point.

Chang: You bring up a good point. There are two thoughts I had from this discussion. One: The symptoms of IBS can be unpredictable, and they can fluctuate. Sometimes, food bothers a patient and another time, they can tolerate fine. It gets confusing for patients because their symptoms are unpredictable, so they just remove it from their diet and restrict more and more rather than trying to find consistent food triggers and avoid or minimize those Do you find that as an issue?

Chey: Absolutely. It's one of the things that's potentially attractive about the FODMAP theory is that it may not be the individual food. It may be more of the cumulative load associated with the total FODMAPs that you eat in the day. That's one thing that makes some sense and provides a potential explanation for why there's this inconsistency from day to day. This is why an integrated approach, with behavioral interventions as well as diet interventions, is so important. A lot of times, patients are completely unaware of all these things that we talked about. If you point out to them the way that they're over restricting or even that they are over restricting, that can be a huge benefit in and of itself. A lot of patients just don't realize the vicious cycle that they've gotten into.

Chang: It becomes a new normal. Could you tell our listeners the patients we should not be advocating a low-FODMAP diet to, in addition to what you just said? Are there other factors we should consider?

Chey: I think most people are able to recognize patients with anorexia. Obviously, you do not want to put a patient with anorexia on a highly restricted diet. Bulimia is a little bit trickier to pick up, but I think everybody is aware of bulimia. The one that I think people are less familiar with is avoidant/restrictive food intake disorder (ARFID), and that's particularly prevalent in GI patients. In fact, our studies, as well as studies from the Boston group, suggest that probably upwards of 15% of patients seen in general GI clinics qualify as or have characteristics that are concerning for the possibility of ARFID. ARFID is not just being a picky eater. There are lots of people that engage in restrictive activity, just as you alluded to, but don't rise to the level of qualifying for the diagnosis of ARFID. ARFID is restricting to the point where it's dangerous. For example, you're developing clear nutritional deficiencies, you're requiring nutritional supplements, or you're requiring enteral feeding or total parenteral nutrition (TPN). For patients with ARFID, you do not want to prescribe a restrictive diet. In fact, it's important to recognize the possibility of ARFID to make sure that you address it in an appropriate way and refer that patient to a healthcare professional who has experience in eating disorders and disordered eating.

Chang: That's really important. Would you use a low-FODMAP diet in the different bowel habit subtypes? I know that there is evidence that it can help the diarrhea predominant, the mixed bowel habits, and even constipation, although it's studied less in the constipation subgroup. What are your thoughts about the bowel habits subgroup?

Chey: We presented some of the first large-scale data on this at the American College of Gastroenterology meeting this past fall. There have been a few studies that have included all-comers in terms of IBS subgroups, but the studies that have been published to date have been in 10 or 15 patients. By the way, those small studies have suggested that there is benefit for the overall symptoms in patients with IBS with constipation (IBS-C). The evidence base has been so poor that people have not had confidence that there's benefit. We presented a purely observational study, not a randomized controlled trial, where individuals utilized a pre-set low-FODMAP meal plan, and it looked at clinical outcomes in individuals of all subtypes of IBS, so IBS with diarrhea (IBS-D), IBS-C, and IBS with a mixed bowel pattern (IBS-M). Bottom line is that the benefits for overall symptoms — abdominal pain and bloating — were very similar and not statistically significantly different among the three subgroups. For the first time, in a large, real-world study with hundreds of patients, it was suggested that low-FODMAP offers benefits not just to people living with IBS-D, but also IBS-C and IBS-M.

Chang: That's good to know, it's and an important pearl in clinical practice. I want to talk more about your personalized approach to seeing patients in clinic. How do you approach using dietary interventions in your patients with IBS?

Chey: The first thing I try to understand is the patient's relationship with food. Again, that gives you some insight into whether the patient views food as an enemy and is over restricting. That's something that I do coming right out of the gate. The other thing that I try to understand is what, specifically, they've done — what foods they've excluded, and what diets they've tried. Increasingly in 2023, a lot of the patients who come to see me have already tried the low-FODMAP diet. I think in that circumstance, it is important to understand and ask, "Was that with the help of a dietitian? What kind of education did you receive? Did you go through all three of the phases, or just tried it for a week and stopped?" What you'll find is that a lot of the patients who said they have "tried" the low-FODMAP diet really haven't tried the low-FODMAP diet. In my case, we're very lucky to have the assistance of well-trained, expert GI dietitians. I've been playing around a lot with other diet strategies. We have a lot of studies looking at things like sucrase-isomaltase deficiency and IgG base testing. We're also starting a study right now on Mediterranean diet compared to the low-FODMAP diet. We have probably four or five diet studies going on at any given time that patients who are interested can enroll in.

Chang: When you were talking about assessing how patients practiced the low-FODMAP diet, it reminded me of what we should also do with any other treatments. Someone may say, "I've been on that medicine, and it didn't work." But maybe we should ask, "What was the dose? How long did you use that? What was the expectation of what symptoms you were going to improve?" There are a lot of follow-up questions to assess how any treatment is being utilized by a patient.

Chey: You're absolutely right. I would remind people about the VA co-op study that Stu Spechler published about gastroesophageal reflux disease where patients who had failed the twice-daily proton pump inhibitor (PPI) were enrolled into a study looking at a bunch of alternative strategies, one of which was talking to the patient, providing them with scripted instructions on how to take their PPI. That led to around 15% of the patients getting better just with talking to them about how to appropriately take their PPI.

Chang: That's really interesting. It always comes down to communication. You work with GI dietitians in your practice, but there are clinicians and patients who don't have access to GI dietitians. What resources or what information can we provide them?

Chey: The good news is there's lots of information. The bad news is there is a lot of information. There is a lot of stuff you can find on the internet. I would really stick to credible sources. Some of them, like the Monash University website, have a lot of information about diet therapies and, specifically, the low-FODMAP diet. There's also another group called the GI Institute, which is a consortium of international GI dietitians who are putting together educational materials as well. That's a good source. Kate Scarlata and Patsy Catsos have excellent websites that have lots of free information for patients, and now there are lots of books. I've written forewords for probably four or five different books on the low-FODMAP diet by people like Tamara Duker Freuman, Kate Scarlata, Patsy Catsos, Rachel Pauls — all of them have written excellent books on the low-FODMAP diet that can hold the patient's hand as they try to execute the diet in their day-to-day lives.

Chang: That's great information. I want to end our interview with a question to you. What key messages about diet in IBS would you like to convey to the audience? And what do you see for the future?

Chey: The first thing is food is the single most important trigger for symptoms in patients with IBS. It'd be wonderful to be able to sit here and tell you that there's one unifying mechanism as to why food causes problems, but there isn't. Food is complicated. I always use that term when I'm talking to patients: Food is complicated. There are many reasons why an individual might have an adverse reaction to eating a food. Further research to understand those mechanisms will lead to advances in developing diet interventions for patients with IBS. Right now, the most evidence-based diet is the low-FODMAP diet. It's really important to remember that there are three phases: restriction, reintroduction, and personalization, and that the diet is best and most effectively administered with the help of a GI dietitian. If you don't have a GI dietitian, make sure that you have a suite of resources available for the patient. Please don't just hand them a sheet of paper with a bunch of foods on it and say, "Have at it." It's much more complicated than that, and you're really doing a patient a disservice if that's the way you're administering the low-FODMAP diet. There are other diets on the horizon. I think a really good way to think about this is the low-FODMAP diet was our entry into the diet space. We're at the beginning, not the end. There's going to be a lot more coming in regard to diet therapies for patients with IBS. Where are we going? I think where we're going is the pursuit of personalized nutrition. Lin, you alluded to this during the podcast already because you and I have spoken about this many times. The bottom line is that I don't think that any diet therapy is going to make everybody better. It's a heterogeneous group of patients. Therefore, the solutions will be heterogeneous, and it'll be important for us to develop biomarkers or diagnostic tests that parse patients on the basis of what is causing their symptoms. That will allow us to choose the right diet therapy for the right patient. There's preliminary evidence from studies suggesting that approach is at least a possibility. I have a lot of work to make that a reality. But preliminary studies really do suggest that there may be signatures in the microbiome, the metabolome, and bile acids that might allow us to choose the right diet therapy for the right patient.

Chang: Thank you, Bill. You shared so much wonderful information, a lot of insights, and a lot of practical information. Today we had Dr Chey discussing the relationship of food and IBS: how food could be a trigger but medicine as well. There's going to be much more to come in the future. Thank you for joining us. This is Dr Lin Chang for InDiscussion.


Irritable Bowel Syndrome (IBS)

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Proton Pump Inhibitors (PPI)

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