Lin Chang, MD, on Exclusion and Restrictive Diets in IBS

In this podcast, Dr Chang discusses her research into the impact of exclusion and restrictive diets on the gut microbiome and how that may affect patients with irritable bowel syndrome.

 Lin Chang, MD, is the vice-chief of the Vatche and Tamar Manoukian Division of Digestive Diseases, program director of the UCLA GI Fellowship Program, and codirector of the G. Oppenheimer Center for Neurobiology of Stress and Resilience at the David Geffen School of Medicine at UCLA.

TRANSCRIPT:

Hello, everyone and welcome to another podcast from the Gastroenterology Learning Network. I'm your moderator, Rebecca Mashaw, and I'm delighted to be here today with Dr. Lin Chang, Vice Chief of the Manoukian Division of Digestive Diseases, and a professor of medicine at the David Geffen School of Medicine at the University of California at Los Angeles.

She's going to discuss her recent research into the effects of exclusion and restrictive diets on the gut microbiome and how this may affect severity of disease and symptoms among patients with irritable bowel syndrome. Thank you for joining us, Dr. Chang.

Dr. Lin Chang:  Thank you so much for having me.

Gastroenterology Learning Network:  You noted in your article that diet is rarely evaluated in studies of the microbiome and IBS. Why did you decide to undertake a study like this of this relationship, and of exclusion and restrictive diets on the microbiome of patients with IBS?

Dr. Chang:  Our research center was very interested in the pathophysiology of IBS, and trying to understand this very complex but very common condition that's now known as a disorder of gut-brain interaction. It's the way the brain and gut communicate. Part of that brain-gut communication extends to the microbiome, so now it's termed brain-gut microbiome access or interactions.

There's been a lot of studies out there in different parts of the world where they've tried to compare the fecal microbiome in IBS patients versus a control population, usually healthy individuals, and there's a lot of variability on the response. One of the typical comments that authors make is well, diet can affect the microbiome.

Maybe some of these differences or the variability between studies has to do with the variability in diet. There hasn't been very many studies where they've looked at specifically diet other than a diet study, like the low FODMAP diet, which you've probably heard of. That's probably one of the most common diets that IBS patients use to treat their symptoms.

We wanted to look at a larger group of IBS patients and healthy controls, look at the fecal microbiome, but specifically, identify if diet can change the microbiome or affect it so that we would at least know that if a patient was on a particular diet, what would we expect the microbiome changes would they have?

It's probably hard for all of us to document what diet the patient is on because it has to be by patient report unless you're feeding them a specific diet.

What we tried to do is we have something called a diet checklist, where we give the different types of diets a description, and then we also measure a food frequency diet, or DHQ, which is a validated instrument on the frequency of different foods that a patient eats. Then we also did a 24-hour recall and we determined what diet the patient was on.

What we were specifically interested is in whether a patient on an exclusion diet restrictive diet is different than them being on a standard or nonexclusion diet, a standard American or modified American diet, or even a Mediterranean diet, which we don't consider an exclusion diet, not really excluding so many different types of foods.

The other point I just want to make is that we know that two-thirds of IBS patients will report that food makes their symptoms worse, that they have food-related symptoms. That makes sense to patients and to health care providers that you can modify your diet to improve your symptoms.

GLN:  Can you give us a brief overview of the study, the number of patients, the types of studies you did, definitions of terms? Just the key points of this particular research project.

Dr. Chang:  Yes. Patients who come in our center are doing a type of research study. We're not taking just any random community type of patient population. We have 346 patients with IBS and 170 healthy control individuals. Those are patients that don't have GI symptoms or any chronic pain conditions or psychological symptoms.

We collected their stool and we measured the microbiome. The way we did is we use 16S sequencing, this ribosomal RNA, which is a standard sequencing technique to measure Alpha and Beta diversity.

Then we just compared IBS versus controls, and then we looked, within IBS, we compared those on a restrictive diet and those who are not on a restrictive diet because basically, most healthy individuals do not go on a restrictive diet. Basically, we only had to do that comparison within IBS.

GLN:  Did you find that patients with IBS do in fact often use restrictive and exclusion diets?

Dr. Chang:  In our patient population, I think it was about 27% of IBS patients were on a restrictive diet and about 8% of healthy controls were on a restrictive diet. I should define our exclusion or restrictive because that gets confusing.

An exclusion diet meant that individuals will exclude foods for perhaps nutritional or healthy reasons. It wasn't necessarily because of the symptoms or disease. Someone who was on a vegan diet or vegetarian was considered an exclusion diet. Only Mediterranean, American, and modified American were the regular standard diets.

Within the patients on exclusion diet, they were on a restrictive diet if they excluded foods in addition because of their symptoms. That would include gluten-free diet, dairy-free diet, low FODMAP diet, which were considered exclusion diets, but we call them restrictive because they're restricting it likely because of their GI symptoms.

GLN:  Thanks for that clarification. Were those among the most commonly used diets that you found that the IBS group turned to: gluten-free, low FODMAP, dairy-free?

Dr. Chang:  We found more of the gluten-free and dairy-free. We had less patients on a low FODMAP. It might be because low FODMAP diet, you're only supposed to be on it for a set period of time. It's only supposed to be about 4 weeks, 6 weeks. If it doesn't work, you're supposed to return to your regular diet and just remove any foods that you think are consistent triggers.

It may just be that we just didn't have anybody on a low FODMAP diet, or we have very few people on a low FODMAP diet at that time because patients want a gluten-free diet and dairy-free, that tends to be long term.

GLN:  Did these diets appear to change their fecal microbiota?

Dr. Chang:  If we looked at patients with IBS versus healthy controls on a standard diet, we didn't see much difference. If you looked at patients on exclusion diet, IBS patients, versus not on exclusion diet, we did find some differences.

The main differences we found is those patients on exclusion diet had an increased abundance of Lachnospira, which is a certain genus. That bacteria makes short-chain fatty acids that are nutritional and healthy for the epithelial lining and they can also increase mucus production. Mucus helps our barrier function. It helps to keep it protected, and this spectrum tends to increase with patients on plant-based diets or vegetarian diets. Some of the patients were vegan or vegetarian. That was probably some of the reason why Lachnospira was increased.

What we found is patients on exclusion died, they had less eubacterium. That tends to be reduced in patients on a gluten-free diet. That might explain that as well. Patients on a restrictive diet, they tended to have less lactobacillus, which would likely go down if you're on a dairy-free diet or a gluten-free diet. Those were the main differences we found.

GLN:  What here is cause and what is effect?

Dr. Chang:  That's a good question.

GLN:  Patients with IBS are using these restriction and elimination diets because of their symptoms to try to help alleviate those, but do the diets themselves cause changes that could exacerbate their condition?

Dr. Chang:  That's such a great question and that's the key clinical practice question. We do know in this study—and other studies are showing the same thing— when an IBS patient goes on a restrictive diet, they do have more symptoms.

The thought is they have symptoms that are diet-related and they're restricting foods. That's why they're doing it. Because they have more severe symptoms as opposed to people that don't. That the restrictive diet then causes changes in the microbiome. That can explain some of the findings that we see in the literature.

The alternative is that IBS is a disorder where the microbiome is altered and the microbiome can alter GI function and brain-gut interactions. That leads to more symptoms, so then the patients reduce their food intake.

This is a cross-sectional study. We don't really know that. We do know that the microbiome changes if you institute a low FODMAP diet, so I know a diet does change it. And some of the findings that we had and that were associated with a restrictive diet or inclusion diet, it's been reported in the literature, like plant-based diets or gluten-free diets. We know that diet does change the microbiome.

What I tend to see in clinical practice, which is an issue, is that we do know that restricting certain foods will help patients with their symptoms. But a lot of times it's hard for patients because these symptoms fluctuate with time, and so they'll start excluding foods that they think are causing their symptoms but it may not be a reliable or consistent trigger.

So one day, they may be eating tomato sauce with pasta and they get bad symptoms. Another time they can eat that same tomato sauce, but they'll restrict it anyway because they're not sure if it causes symptoms.

Then what can happen in patients with severe symptoms is they start restricting, restricting, restricting, that there are on very few different foods. Then when they try to reintroduce a different food, a new food, they have symptoms.

I don't really ever know, are they really intolerant to that food or is it because they've restricted it so long that now the microbiome has changed, the gut function has changed, and it's not used to reintroducing foods?

And some of the severely restricted diets, I almost feel like their gut is like the gut of a baby, where they're so not used to taking in foods, that now you have to start very slowly, a very bland diet, and then start gradually reintroducing foods.

In a way, restricting your diet can be helpful, but you don't want to go overboard either. You don't want to start getting into what is now we're finding in IBS patients and some GI disorders that are food-related, of a condition like a disordered eating condition. There's a condition called ARFID. This is avoidant restrictive food intake disorder.

The patients are not doing it because of what they think about their body shape or anything. It's because of this relationship to food and that they initially noted that if they reduce certain foods, they feel better. But there's always a balance that we need.

GLN:  You looked at patients with all subcategories of IBS, including diarrhea-predominant and constipation-predominant. Did you find any distinct differences between these IBS subcategories?

Dr. Chang:  Yes, fortunately, because we had a larger group of IBS patients, we were able to compare IBS with constipation, IBS with diarrhea, and IBS with mixed bowel habits, meaning they'd have both diarrhea and constipation. We did find some differences between IBS with constipation, IBS with diarrhea.

The IBS with diarrhea patients had a greater abundance of Lachnospiraceae, Blautia, Lachnospira, and a bacteria that I'm not going to be able to pronounce its microbe, Erysipelotrichaceae, [laughs] and a lower abundance Lachnobacterium.

There are some differences by the bowel habit. They weren't so much differences by whether they were on a restricted diet or not, so I don't know really the clinical meaningfulness of this, but we do know that microbes can be altered based on transit time to the gut.

Transit time actually is an important factor in bacteria and we do know that these two different bowel habits subtypes can have different transit times. IBS-diarrhea being more rapid than the IBS with constipation.

GLN:  What can a practicing gastroenterologist take from this study that would then help them in working with and advising their patients with IBS in regard to their diets?

Dr. Chang:  They should know that diet can affect the microbiome, and especially if you're on a restrictive diet. What we don't know is if you restrict your diet to a point, that the microbiome changes, that that can, in turn, lead to more symptoms or even less tolerance of foods that have been restricted for so long. We don't know that.

This study just shows that restricting your diet will alter microbiome and can explain some of the variability of the findings that we see in the studies, but that there are intrinsic differences that IBS patients have versus healthy controls, but the diet will explain some of those findings.

GLN:  Any last thoughts you'd like to share either from this particular study or just from your practice with working with patients with IBS?

Dr. Chang:  The important part is that the microbiome is important. That the microbiome is part of the whole orchestra of the whole person. It's one component and it's an important component. In some patients, by altering it, whether it's diet or antibiotics, may be helpful. A lot of times you have to look at everything else.

There might be central related factors that are important, and so you don't want to treat every patient the same. It's the important violin section of the orchestra, but there's also many other parts in the whole person that are important too to pay attention to.

We're going to move to microbial metabolites and not just the type of microbes. I think we're going to have a lot more data that will have us understand the role of the microbiome in IBS and many other conditions and just in general health.

GLN:  Thank you very much for talking about this today. We appreciate your insights into the subject and look forward to checking in with you again for future research and what you find out about those metabolites.

Dr. Chang:  Thank you so much.