Gut Check: Darren Brenner, MD, on Bloating and Distention

In this episode of Gut Check, host Brian Lacy, MD, and guest Dr Darren Brenner discuss the common symptoms of gas, distension, and bloating--what distinguishes each from the others, possible causes, and how to treat these prevalent conditions.

Brian Lacy, MD, PhD, is a professor of medicine at the Mayo Clinic in Jacksonville, Florida. Darren Brenner, MD, is a professor of medicine and surgery at Northwestern University in Chicago, Illinois.

 

CLINICAL PRACTICE SUMMARY

Gas, Bloating, and Distension: Clinical Approach to Evaluation and Management

• Condition and definitions: In outpatient gastroenterology practice, gas and bloating symptoms are highly prevalent, with international literature cited as affecting about 1 in 5 or 6 individuals. The discussion distinguished bloating as a subjective sensation of excess gas from distension as an objective, visible abdominal enlargement; patients may have either symptom alone or both together.
• Evaluation and testing: The differential diagnosis described was broad and included small intestinal bacterial overgrowth (SIBO), methanogenic or sulfur-related overgrowth, celiac disease, gastroparesis, neuromyopathic disorders, hypothyroidism, diabetes, carbohydrate maldigestion or malabsorption, and disorders of gut-brain interaction such as IBS, functional dyspepsia, and constipation. The experts advised against a shotgun testing approach and said testing is not necessary in all patients. Dr Brenner usually checks for celiac disease and noted that 10% to 15% of people with celiac may present with constipation.
• Breath testing and management: When breath testing is pursued, a glucose breath test is often more specific than lactulose. Proprietary breath tests are misread 20% of the time (1 in 5) in their program at Northwestern. Management should target the underlying cause; for intestinal overgrowth, the most robust data are for antibiotics, especially rifaximin, while behavioral approaches such as cognitive behavioral therapy, gut-directed hypnosis, diaphragmatic breathing, and visceral biofeedback may help selected patients.

 

 

TRANSCRIPT:

Welcome to GutCheck, a podcast from the Gastroenterology Learning Network. My name is Brian Lacy. I'm a professor of medicine at the Mayo Clinic in Jacksonville, Florida. I am absolutely delighted to be speaking today with Dr. Darren Brenner, professor of medicine and surgery at Northwestern University in Chicago, Illinois. Dr. Brenner is a nationally recognized expert in disorders of gut-brain interaction, including irritable bowel syndrome, functional dyspepsia, and chronic constipation. However, one of his other areas of expertise, both clinically and for research purposes, revolves around the very prevalent symptoms of gas, bloating, and distension. So Dr. Brenner, welcome. What a delight to have you here today. Let's set this stage for our audience. How common are symptoms of gas and bloating?

Dr Brenner:

So Brian, thanks for having me first and foremost. And I think this is a really great place to start because this is a common symptom. And I think it's interesting. If we go back 20, 30 years, this is not something that most people endorsed or brought as a chief complaint to our clinical practices, but now it's pervasive. I mean, I probably, if I see 20 patients a day, 18 as part of their symptom profile will endorse these symptoms. And I think internationally, recent literature suggests that it's about one in five or six individuals. So something that is happening more and more often. And of course the questions become why, and that's what we're all trying to figure out, right?

Dr Lacy:

So incredibly prevalent symptoms and bothersome, but to make sure we're kind of using the same language here, what's the difference between gas and bloating and distension? Do these terms mean all the same things to patients and providers or are there important differences?

Dr Brenner:

I think that they do mean the same thing to most patients and practitioners and providers, but I think we need to start looking at these as kind of mutually exclusive or overlapping types of disorders. People who say that they have more gas, we'll usually define it as I'm passing more gas or flautus, or they're belching more frequently. People will combine bloating and distension, but really physiologically, these are two different processes. I tell my patients, bloating is a subjective phenomenon. You feel like there's too much gas in your system. You want to get it out. The analogy I'll give my patients is, do you feel like there's just a gas pocket in there? And if you could pop the bubble or if you could put a Dyson vacuum cleaner down your throat and suck it out, you feel much better. And they say yes versus distension.

So distension, I say, is objective. We can see it. These are the people that walk in the door and they say, "I look like I've done a hundred crunches this morning. I can see my 6-pack, but at the end of the day, I look nine months pregnant." And they bring us pictures, right? They show us the before and after. Here's me in the morning, here's me at night. And I think we'll get into this a little bit more, but this is a completely different process or phenomenon from my standpoint, but it's important to note that people can have overlapping of both of them. Many people complain of both at the same time.

Dr Lacy:

Great. So it's such a great teaching point that bloating is really that subjective sense of gas, that air-filled balloon, as you kind of mentioned, and distension is that visible manifestation, something we can measure. So Darren, what are some of the most common causes of bloating?

Dr Brenner:

So I think the most common in the lay press is intestinal overgrowth. And most people will just define this as SIBO or small intestinal bacterial overgrowth, but we also know that there are methanogenic overgrowth, sulfuric overgrowth, which are associated with different disorders—constipation and diarrhea respectively. And I think we talk about this first and foremost because this is what's in the lay press. This is what you look up when you see bloating and distension. There's all kinds of things about SIBO, knowing there's more than that. But there are many other phenomena that are associated with these symptoms—other biologic conditions like celiac, many of our patients present with bloating and distension. Gastroparesis, neuromyopathic disorders, people who present with things like scleroderma, Parkinson's, ALS, MS, anything that can slow down the GI tract, more commonly hypothyroidism or diabetes. People will relate this to the foods that they eat.

Different foods can lead to gas, bloating and distension. People can have difficulty digesting and absorbing disaccharides like sucrose or lactose or isomaltose or maybe we drink too many carbonated beverages, our Cokes and Pepsis, which are full of fructose, which can overload our systems and we're not able to absorb those. This is just kind of the base of the iceberg of the things that can cause these symptoms. And then there are disorders of gut-brain interaction, what we used to call functional GI disorders, where visceral hypersensitivity can play a role—disorders like irritable bowel syndrome, functional dyspepsia, constipation, and the list goes on, even functional bloating. There are people that are just out there that feel this gas-like pressure every day with no other symptoms whatsoever. So it's a very, very broad differential diagnosis for the things that can cause gas, bloating and distension.

Dr Lacy:

So it really seems like as a provider, and although you're the expert in the field, you really need to put on that detective cap to really sort through these symptoms and try to identify the underlying cause. And let me just follow that up a little bit about thinking about the underlying cause. So can you distinguish, for example, if someone has severe bloating every day, is that more likely to be caused by small intestinal bacterial overgrowth to somebody who maybe just has intermittent bloating and maybe that's lactose maldigestion? Does that help us?

Dr Brenner:

I have not found that in ... I found in many cases that the answer to that question comes from a good history and physical exam, looking for the bloating and distension and asking other questions. I mean, is it secondary to another process? Well, if you have something in your history like diabetes, diabetes slows gut motility, can increase the likelihood of pretest probability for bacterial overgrowth, and it may be something that I consider versus constipation. Many people with constipation come back with bloating and distension because things are backing up, they're stretching the wall of the intestine, they have visceral hypersensitivity, or maybe there's more of a fermentation process going on there. So I really think it's a matter of starting with that broad differential diagnosis, asking the right questions to tease things out, and then knowing where to go with diagnostic strategy, as opposed to kind of a shotgun approach where we run a whole bunch of tests and hope that something sticks and then treat that, assuming that the diagnostic studies that we use are perfect and are actually giving us the right answer.

So I think the simple answer to your question, Brian, is the same thing we learned the first day of medical school. Ask more history if you're not sure where to go.

Dr Lacy:

All right. And another great teaching point, that probably just doing a shotgun approach with a battery of tests that probably isn't very cost-effective and it may not reassure your patient. So let's be more thoughtful.

Dr Brenner:

Exactly.

Dr Lacy:

So can you guide our listeners through their process of why underabsorbed lactose or fructose could cause symptoms of gas and bloating? Aren't these common food substances really easily absorbed by the small intestine?

Dr Brenner:

They should be easily absorbed by the small intestine, but first they have to be digested into monosaccharides, or specifically when we talk about things like lactose. Lactose is a disaccharide. It has to be broken into its elemental products, which are glucose and galactose to be able to be absorbed. So if we don't have enough of the enzyme lactase in the GI tract, and that can be due to a genetic deficiency, that can be due to destruction of the intestinal lining by things like celiac, H. pylori, other common disorders like bacterial overgrowth, then you lose the enzymes to break down these sugars. These sugars make it farther down the GI tract where very commensal symbiotic, healthy bacteria are, but they use these sugars as their nutrient substances as well. And while many positive things can come out of the digestion of these sugars, we also get the byproducts, which are things like hydrogen, methane, carbon dioxide, the gases that are there that cause people to feel this kind of more bloating phenomenon or pass more gas.

Now, fructose is a different issue. Fructose is a monosaccharide. It does not need to be broken down, but there are specific receptors in the gut that help us absorb fructose. And if you drink too much or you consume too many products that have high levels of fructose in them, you can overload the system. You can basically oversaturate the system to the point where it can't absorb anymore. And the same process as the lactose, the sugar gets down into the distal portions of the small intestine and colon with the bacteria there converted into gas. So there are multiple different processes here at play that can lead to malabsorption and maldigestion.

Dr Lacy:

Darren, I like what you said an awful lot about kind of overwhelming the system with fructose. So as an example, maybe somebody who drinks juice with breakfast and then they have some fresh fruit and then they drink a regular soda with high fructose corn syrup and then more fresh fruit, and then they maybe drink some sports drink. They've just overwhelmed that system, right?

Dr Brenner:

Exactly. It just can't keep up. And so you get this malabsorption in the secondary fermentation of the sugar.

Dr Lacy:

Let's transition a little bit because you mentioned testing before. And let's think about maybe a typical patient you might see in clinic who reports months of issues with gas and bloating and distension. You take that great history, you do that exam, you don't identify any warning signs. They're not anemic. They're not losing weight. There's no family history of a gastrointestinal malignancy or inflammatory bowel disease or celiac disease. So is testing necessary? Should we be performing tests in all of these patients? And if you do decide to do a test, what test might you perform?

Dr Brenner:

So I would say that testing is not necessary in all individuals. It's a little bit of shared decision making. As we just mentioned, a lot of this can relate to diet and many people come in and they've tried different diets that have either partially worked or been successful and they've identified specific foods that can fall into categories like fructans, for example, which is a very common fermentable carbohydrate that can be turned into gas. So we can start with things like that. Most of the therapies that we use are pretty benign, right? Antigas medications, simethicone, probiotics, herbal supplements, those sorts of things can be attempted for a few weeks at a time to see whether or not they're effective before we have to go into diagnostic testing.

I do like to look for celiac because celiac, which is an autoimmune disorder that attacks the lining of the small intestine, is more than gas and bloating. It's associated with vitamin and micronutrient deficiencies, bone demineralization in women, infertility miscarriages, transaminitis, cardiac issues, and more importantly, increased risks of cancer. I do not want to miss that one. So I will be honest and say that in most cases, I will look for celiac, whether it's diarrhea, which is more common in people with celiac, but even constipation because about 10 to 15% of the population with celiac can present with constipation as well.

I think the big question or the question you're getting at is, when do we start doing breath tests and other tests for intestinal overgrowth? And that is not first and foremost in my algorithm, but it is if the patient asks for it because we know that a lot of labs are not doing this test on their own. Yes, academic centers do, but a lot of these studies are done by proprietary companies. And we showed a couple of years ago that the vast majority of these companies do not interpret these tests based on consensus international guidelines. So people get a test response that's either a false negative or a false positive based on our studies 20% of the time. So 1 in 5 individuals that came to our program that had a proprietary test had a misread. So if my patients ask for it, I do it because I know if I won't do it, somebody else will, and I want to make sure they get the right interpretation, but I also tell my patients two things. Number 1, these breath tests are not perfect. And number 2, the elevation in breath gases, whether it's hydrogen, methane, or hydrogen sulfide, may be nothing more than an epiphenomenon, meaning that we detected a gas, but it may be playing a partial role, a full role, or absolutely no role in their symptom profile. And we have to keep that in mind. Too often do I see people put all their eggs in one basket— We're getting closer to Easter, so I like the analogy there, but they say, "I had this positive hydrogen level at one point in time X number of years ago, and it is the cause of all of my ills, both gastrointestinal and extraintestinal, and it probably isn't in the vast majority of cases.

Dr Lacy:

Important to keep a good perspective about this and with the entire holistic approach that you obviously practice. And just to mention, because you're too modest for our listeners, Dr. Brenner has a very nice review article coming out about breath testing and bloating in the American Journal of Gastroenterology later this spring. So keep your eyes peeled for that.

So speaking of breath testing, so let's focus on that. If you decide to do a breath test, there are several different options available, several different choices. Where do you like to start?

Dr Brenner:

Yeah, I start with a glucose breath test. I know there's a glucose breath test, the lactulose breath test. I know some of our colleagues, if they listen to this later, will probably crucify me for saying glucose, but I tell everybody this, this is confusing. When you come to see a practitioner with regards to testing for intestinal overgrowth, this is a very confusing process because you want answers, you deserve answers, but we don't have all of the answers you're looking for in 2026. So my first response to my patients is I'm going to be as honest with you as possible about what we know from an evidence-based standpoint and what we don't know. And to mention that paper, you're very modest as well. You're obviously involved in that project as well. So we really did try to tell you what we know and we don't know.

Why do I pick glucose? I want something that I think is more specific. If the test is positive, it's more likely to be positive as opposed to lactulose, which I feel is more sensitive; it's going to pick up more people, but a lot of these people may not have their symptoms due to the positive breath test. So I use glucose. We at Northwestern, we do not do the test in-house. I don't want to commercialize our market for a specific company, but I will say there is a company out there that measures hydrogen, methane, and hydrogen sulfide and does assess the results based on the North American Consensus Guideline, which was published in the American Journal of Gastroenterology by Mark Pimentel, Satish Rao, Rick Saad, and other colleagues a few years back. So there is where I get my data and I go for my information on how to do the tests and when to do the test.

But stay tuned, ladies and gentlemen, hopefully in the next 12 months or so, more information forthcoming on how to do breath tests, not only for intestinal overgrowth, but carbohydrate maldigestion and malabsorption.

Dr Lacy:

So another great teaching point is if you decide to embark on breath testing, and if is a good word, then you would start with a glucose breath test looking for bacterial overgrowth or excess methane production or hydrogen sulfide before you pursue a lactose breath test or a fructose breath test. Is that correct?

Dr Brenner:

Absolutely. That's key. You have to make sure that you don't have evidence of bacterial overgrowth because remember, the symptoms of bloating, distension, as we mentioned earlier, I don't like to overlap those, but I know people think of them as one, but the symptoms of excess gas are related to sugar fermentation. And if you give a sugar to a bunch of bacteria that are in the area where the body wants to digest and absorb said sugars and it can't, then the bacteria will do the job for us and you will get false positive results. You'll get a positive study that is not due to the fact that you can't break down or absorb these sugars, but due to the fact that the bacteria that are there are fermenting them before your body has a chance to digest or absorb them.

Dr Lacy:

So Darren, you nicely pointed out that right now in terms of testing, maybe the science is not as precise as it could be, but this is how medicine and science evolves over time. But what about testing for symptoms of gas and bloating and other tests? I mean, as an example, is there any value to performing an upper endoscopy or a colonoscopy? Should we be doing CAT scans in all these patients? What do you think?

Dr Brenner:

Well, I'm an antiradiation person. So if you have isolated gas and bloating, it's very rare that I'm going to recommend a CAT scan for something like this. I think it's based on the other symptoms that are present. Are there alarm signs or symptoms? Is there unintentional or unexplained weight loss? Was there an acute change in bowel habits? Is somebody having persistent vomiting? These are situations where absolutely I am going to take a look and see if there are other issues involved, other causes of dyspepsia like H. pylori or celiac, or God forbid, colonic obstruction. We're seeing these in younger and earlier individuals. So we don't want to miss those alarm signs or symptoms, but for isolated gas and bloating, probably the most common study that I do is an abdominal x-ray, and I do that for two reasons. Number 1, I want to qualify, I won't say quantify, but qualify the amount of stool in somebody's colon because if they are loaded from stem to stern or ascending colon cecum to rectum, I probably have a pretty good sense of what's going on.

People will present and say, "I have a bowel movement every day. It's a normal texture bowel moment. There are no other symptoms," but it may be a very small bowel movement and there's residual stool leading to other symptoms that they may be experiencing.

The other reason I get an x-ray is to kind of validate to a patient who has abdominal distension that it may be due to something other than gas, because if I can get an X-ray, bring it up on the screen and say to the patient, "Here's what gas looks like," and you don't have any of it, then that gets buy-in from the individual that we need to look in a different direction. So I use it to validate my thought process in terms of my diagnostic strategy.

Dr Lacy:

Interesting. We haven't really talked about this before, but I think I now do more abdominal X-rays than in the past. And I think you're right. If you can show this huge stool burden or a lack of gas, I think that can be very informative and direct you in another pathway. And as you kind of mentioned before, constipation is frequently associated with gas and bloating. And we know that many people who have trouble evacuating stool from the studies from Juan Malegelada and Fernando Azpiroz also have problems moving gas through the GI tract.

So let's shift gears for a second and think about treatment. So there must be a validated treatment algorithm out there for all patients with gas and bloating, right? Isn't there some great flow chart we can use to really improve all these symptoms?

Dr Brenner:

I'm trying not to laugh as you say that. I can see the smile on your face as well. The simple answer is no. We're not even close. How we treat this is really predicated on what we define as the underlying problem. And then we go after that directly. If it's celiac, it's a gluten-free diet. If it's diabetes, we want to make sure that blood sugars are well controlled because we know the higher the blood sugar, the lower the motility in the GI tract. So your GI tract is going to slow down. If it's constipation, we want to treat that appropriately, whether it is slow transit constipation or pelvic floor dysfunction. Obviously there are differences there. I will say that if we're talking about intestinal overgrowth, from my standpoint, the most robust data is for antibiotics. And my antibiotic or my favorite antibiotic is rifaximin. It's safe. It has minimal penetration outside of the GI tract. And there's some very good data out of Mark Pimentel's lab showing that it probably is the most effective antibiotic. Some people will cycle antibiotics over time. I don't personally do that in my clinical practice. Probably another question for another time. And then we talk about whether or not there are ways to tweak the antibiotics if somebody has increased methanogenic production or hydrogen sulfide.

But the take-home message and the short message is no, it's different strokes for different folks. Some people try probiotics. There really isn't good evidence-based data for that. Some people try diets. There's a little bit of data for elemental diets. I think that's a slippery slope personally for a young individual who may have some disordered eating or fears of eating because of their symptoms anyway. So until there's stronger data, it's a little bit of mix and match, throw a dart at a board, and kind of hope it sticks.

But my personal thought on this is I'm willing to do anything as long as it's safe, to try and help these symptoms. I am honest with my patients and say in some cases we will not get these better, but bloating and distension are not things that are associated with increased risk of cancer or increase your rate of mortality or anything like that. They're things that we have to learn to deal with. And that's when things like cognitive behavioral therapy, gut-directed hypnosis come into play.

One thing we haven't mentioned yet is the distension, the abdominophrenic dyssynergia. I don't know how deep you want to delve into that, but there is really good data showing that diaphragmatic breathing, gut-directed hypnosis, and visceral biofeedback can be very beneficial for that particular disorder. And that's one of the reasons why I get the x-ray to prove to my patients that when they blow up and they look 9 months pregnant, it is not an excess gas phenomenon.

Dr Lacy:

So maybe thinking about our patients who might be listening, keep in mind one size does not fit all. There are many therapeutic options out there, so discuss it with your providers. And for our providers, there's more to this than just giving simethicone. Really try to think about the underlying process and then personalize your treatment.

So Darren, you mentioned that some patients with symptoms of bloating may report their symptoms in part because their gut is more sensitive than others. We oftentimes refer to this as visceral hypersensitivity, and recognizing that this is a very complicated topic. If testing is completely normal and the patient has failed some of the therapies you've already mentioned, are there ways to tamp down or dampen an overly sensitive GI tract that might improve symptoms of gas?

Dr Brenner:

Yeah, I think there's both pharmacologic and nonpharmacologic interventions. And I personally, living in an ivory tower with many superb brain-gut behavioral therapists start there. We know that this is a disorder on the gut-brain axis. We know that there are aberrant signals sent from the gut to the brain that the brain misinterprets and sends down this hyperaggressive ‘ouch’ signal. And if we can tampen down those signals a little bit, people do see improvements. And that's get the idea of things like cognitive behavioral therapy, gut-directed hypnosis, mindful meditation.

For people who don't want to do this, for people who don't believe in it, I'll make a very salient point here. If you do not believe in the idea of the gut-mind access or that brain-gut connection, do not go see a brain-gut behavioral therapist. They will not be able to help you. In some cases, then we can go to pharmacologic interventions, the neuromodulators, which we've renamed, obviously, tricyclic antidepressants; SNRIs, affecting both the serotonin norepinephrine pathway. We know we have to trigger both of those to improve pain syndromes. If there is more here than just the pain and discomfort, if it's along the irritable bowel access, we have FDA-approved therapies for treating IBS. And again, if it's other syndromes, depending on what they are, thankfully in 2026, we have newer interventions for treating these patients as well.

So I think, again, it goes back to everything we've said already. Shared decision-making. There's no one right answer for everybody. Come up with the most likely diagnosis and then talk about the options to treat these people because there's no one size fits all answer here.

Dr Lacy:

Darren, wonderful. I've certainly learned an awful lot. We need to have you back every month, but until then, any last thoughts for our listeners?

Dr Brenner:

Yeah, I think the biggest take-home message here is this: If you present or if you want to talk to your practitioner about gas, bloating, distension, number one, think about other associated symptoms. Is there anything else going on in your GI tract or outside your GI tract that may help us lead to a more accurate diagnosis?

Number two, realize that all things that induce gas or abdominal discomfort are not coming from intestinal overgrowth. Yes, a percentage of individuals do have this process and phenomenon. We have colleagues and friends who've done great work showing that this absolutely exists, but it is not everybody.

And then number three, be open to the different types of therapies that we have, but four, be realistic in our ability to treat this. I tell my patients, in the vast majority of cases, I will not cure this process, but if I can improve the symptoms and improve your quality of life, that's an absolute win.

Dr Lacy:

Wonderful. So like a lot of other disorders, we may not be able to cure things, but we're going to do our very best to get things under control.

Dr. Brenner:

Absolutely.

Dr Lacy:

So Dr. Brenner, again, thank you so very much to our listeners on Apple, Spotify, and other streaming networks. I'm Brian Lacy, a professor of medicine at the Mayo Clinic in Jacksonville, Florida. You have been listening to Gut Check, a podcast from the Gastroenterology Learning Network. Our guest today was Dr. Darren Brenner, professor of medicine and surgery at Northwestern University in Chicago, Illinois. I hope you found this just as enjoyable as I did, and I look forward to having you join us for future GutCheck podcasts. Stay well.