Gut Health

Lin: And we call it the nervous system of the gut, the second brain. I don't know if you've ever heard that. And so that's why there's a very strong interaction between the gut and the brain that's really important. That's how we sense what we eat and what's going on in the body. And then the brain sends signals back down. That's when we know we're hungry or we have pain.

Brent: Welcome to the Life Lab by Death Clock. I'm your host, Brent Franson. The mission of Death Clock is to help 100 million people live ten years longer. Today, we speak with Doctor Lynn Chang about gastrointestinal health, basically about tummy troubles. Doctor Chang is a gastroenterologist and professor at UCLA. She's the vice chief of the Division of Digestive Diseases at UCLA.

Brent: She's the director of the Walter and Shirley Wang Center for Integrative Digestive Health. She's the author of more than 185 papers, 75 reviews, and 30 book chapters. She's won multiple awards, and I could keep going with her distinctions. She's a wonderful guest to talk about everything gastrointestinal health. We talk about IBS, and we talk about all of the things that we think of when we talk about stomach aches and tummy trouble.

Brent: She's a wonderful guest. I hope you enjoy.

Brent: Doctor Lynn Chang, welcome to the show.

Lin: Thank you for having me.

Brent: So today I would call it the tummy troubles episode. I think we've all had stomach aches and things going on with our gastrointestinal systems, but I think we all know less about what's actually happening there than we think we do. So I'm excited to dive in and ask you a bunch of basic questions and then get into some things I think that are going to be a little bit more advanced.

Brent: But before we do that, can you give us a sense of your background and your day job?

Lin: Yeah, so I'm a gastroenterologist at UCLA, and I've worked at UCLA for many years, doing a lot of my education and training there. Over the years, I've taken care of patients, specifically a patient population who have what we call IBS or disorders of gut-brain interaction.

Lin: I also do administrative work. I'm the vice chief of our division at UCLA, and I also do research and oversee different programs.

Brent: Wonderful. So can we start with just what the gastrointestinal system is? Does it start at the mouth and end at the anus, going all the way through? Or would we say it starts at the stomach and ends at the end of the intestines or at the colon? Where does it start and stop?

Lin: It starts in the oral cavity, the mouth, and ends at the anus. The main areas are the esophagus, through which we swallow food, and then it goes into the stomach, which I think everyone is familiar with. Then we have about 20 to 23 feet of small intestine that's all coiled up in our abdomen. And then we have the large intestine, or what we call the colon, where we store stool, and then the rectum and the anus where it passes.

Brent: So the large intestine is basically just the colon? It's not a coiled structure like we think of with the intestines?

Lin: It's basically shaped like a question mark. On the right side, in the right lower part of the abdomen where the appendix is, you have the ascending colon that goes up. Then the transverse colon goes across near your stomach area, and then down the left side.

Lin: Then you have the sigmoid colon, and then you have the rectum right in the center, which is the end of it.

Brent: Okay. I think of most digestion happening in the stomach and intestines. I think of the colon as more storage than processing. Is digestion happening in the stomach and small intestine?

Brent: And then the large intestine is just storage prior to exit, or am I oversimplifying it in the wrong way?

Lin: That's pretty close. We eat a lot of different foods and liquids, and the stomach, which has a lot of acid, works at dispersing the food particles into smaller particles so they can pass more easily into the small intestine. Every so often, the stomach will make a sweeping movement to push larger particles along.

Lin: The small intestine is where we do a lot of our digestion and absorption. The colon is primarily to store stool, but it also reabsorbs water. If you've ever seen an ileostomy bag, the stool in the small intestine is very loose, and when it enters the colon, it's still loose.

Lin: Then the water gets reabsorbed, so it becomes firmer as it gets stored. Interestingly, the colon makes back-and-forth contractions like windshield wipers to allow fluid absorption while holding the content.

Lin: Every so often you'll have a propagating wave from top to bottom moving content toward the rectum. Stool can be stored there for up to three days so you don't constantly need to use the bathroom.

Brent: Okay. So when I go to the bathroom in the morning after my coffee, what comes out might have been there for a few days getting ready to go?

Lin: Yes. Many people think what they're eating comes out right after they eat, but it takes time to travel through. We have a reflex in our gut, similar to a muscle reflex.

Lin: When we eat or drink and expand the stomach, a nerve reflex causes the lower colon to contract and help us evacuate. That's why people often go to the bathroom after eating.

Lin: It's a mechanism to keep our gut moving.

Brent: Like a conveyor belt. The conveyor belt starts moving when we put something in at the beginning, pushing something out at the end. Those two things aren't the same. But in the morning, am I exiting what I ate last night?

Brent: Or is it something from a couple of days ago?

Lin: It varies by person. We empty about 90% of what we eat from the stomach in about four hours, and the small intestine takes about five to six hours. The colon takes longer: on average about 30 hours, but up to 70 hours can be normal.

Lin: So unless you have very rapid transit, what you evacuate in the morning is something you've eaten at least a day before.

Brent: So that's how much time it spends at each step: four hours in the stomach—which is why people say to eat your last meal four hours before sleeping—six hours in the small intestine, and then 30 to 70 hours in the colon.

Lin: Yes, that's the general timing. If we get sick or have food poisoning, transit will be much faster because of diarrhea. In people with constipation, it can move slower.

Brent: Is the average speed at which it moves what we refer to when we use the term "metabolism"?

Lin: No, that would be transit time. Metabolism relates to energy sources, nutrients, and how we absorb and process them, which is different.

Brent: Do we use that term incorrectly? For instance, I think of my nine-year-old daughter as having a fast metabolism because she's lean and gets hungry quickly. You're saying that's unrelated to transit time and has to do with how she processes energy?

Lin: There can be a relationship. If things move fast, someone might not absorb as much. With your daughter, it's likely related to her age, activity level, and how she digests and absorbs nutrients. Some people absorb fewer fats and don't gain weight as easily.

Lin: There's a bell curve: some people process faster or slower within a normal range in the general population.

Brent: So the colloquial use of "fast" or "slow" metabolism refers to how much energy you absorb and utilize?

Brent: Wrong.

Lin: It's also about how you use energy. Exercise changes your metabolism. It's not just what you consume and absorb, but how you utilize that energy.

Brent: Does activity level impact transit time? If someone is active, do they process things through the system faster than someone less active?

Lin: Definitely. Being ambulatory and active helps move content through the gut much more than sitting still.

Brent: So if you're worried about flatulence or bloating, going for a walk after a meal can help get the system moving.

Lin: In fact, some people report passing gas while walking for that reason.

Brent: What is an everyday tummy ache? I have four kids, and when they complain of a stomach ache without other symptoms, I'm not sure what to do other than offer water.

Brent: What is actually happening in a basic tummy ache?

Lin: Tummy aches are very common and can have many causes. It could be an infection, intolerance to a food like lactose, gas, or feeling overly full.

Lin: It's a vague description meaning discomfort or pain. Often, tummy aches can also be triggered by stress.

Brent: So it's usually one of a dozen different things, and the body just figures it out and it goes away.

Brent: What would be the most common cause?

Lin: Usually it's food-related, like eating too much or eating something greasy. It could also precede a bowel movement.

Lin: You investigate the symptoms and see if it improves. If it's not serious, distraction and rest help. Observing patterns over time gives you more data.

Lin: If it's persistent or very bothersome to a child, seeking a pediatric consultation is best.

Brent: Is offering water good advice for a minor tummy ache?

Brent: Is that good advice? Bad advice, maybe neutral?

Lin: It's neutral. I try to figure out the cause. In adults, I check for indigestion or heartburn, where something like Tums can help.

Lin: Some people benefit from peppermint capsules. For adults, you check for red flags like diarrhea, blood in the stool, or vomiting.

Lin: If there are no red flags, rest and comfort measures are reasonable.

Brent: Are heartburn and acid reflux the same thing, where acidic stomach contents move up the esophagus, and antacids neutralize the acidity?

Lin: We all produce stomach acid and experience occasional acid reflux into the esophagus. The question is whether it exceeds normal levels.

Lin: Testing can evaluate the frequency and volume of acid reflux. Some patients have increased esophageal sensitivity rather than higher acid volume.

Lin: When true reflux occurs, people can use antacids like Tums, H2 blockers like famotidine, or proton pump inhibitors for more severe cases.

Lin: Brazile those are the class of medications people take when they have more regular, more severe heartburn.

Brent: You mentioned you are lactose intolerant. What happens physiologically in lactose intolerance?

Lin: The enzyme lactase breaks down the lactose carbohydrate in the small intestine. Without enough lactase, lactose travels to the colon where gut bacteria ferment it.

Lin: That fermentation produces gases like hydrogen and methane, causing bloating, gas, and drawing fluid into the bowel to cause looser stools. We produce more lactase when young, and levels naturally decline as we age.

Lin: It is also more common in certain ethnicities, such as Asian populations. Lactose-free milk adds the lactase enzyme directly.

Brent: So lactose intolerance isn't inherently dangerous to your health, but causes discomfort like gas and loose stools.

Lin: Avoiding dairy can make it harder to get adequate dietary calcium and maintain bone strength unless managed with enzyme supplements or alternative sources.

Lin: Yogurt is often tolerated better because the lactobacilli bacteria contain lactase enzymes.

Brent: What happens during acute, occasional diarrhea when someone isn't sick? Is it the digestive system rapidly increasing transit time to clear something out?

Brent: We're going to increase the transit time quickly and so that we don't have that firming process in the colon. It's just basically a rejection of what I've consumed in these cases where it's one time it's not chronic, I'm not sick. But you know, I don't know. We all know those cases where like it happens.

Lin: Greasy or rich foods can alter gut processing and accelerate transit time. Occasional instances are common and normal.

Lin: We look at frequency to determine if it's abnormal, evaluating whether loose stools occur in 25% or more of bowel movements.

Brent: Should you use those occasional reactions to identify personal food triggers?

Brent: And, something I could learn from?

Lin: You can learn from it. Sometimes it's a cumulative effect of what you've eaten throughout the day rather than a single meal.

Lin: That is your that's responding to.

Brent: Is it usually a diet management issue, or can it just be benign normal variation?

Lin: If infrequent, it's benign. Even healthy foods high in fiber can cause temporary gas or bloating while being beneficial overall.

Lin: Everyone responds differently, so individual responses vary.

Brent: On the topic of fiber, what are your thoughts on fiber supplements like psyllium husk or probiotics?

Lin: Psyllium is a well-studied soluble fiber. Fiber is beneficial, and for constipation, target intake is around 20 to 30 grams per day from food or supplements.

Lin: Gut bacteria ferment fiber into short-chain fatty acids, which nourish the intestinal lining and support the gut barrier.

Lin: If dietary fiber intake is low, supplements like psyllium are a helpful addition.

Brent: I take a fiber supplement and had a colonoscopy recently where the doctor noted high fiber intake. What indicates high fiber intake during a colonoscopy?

Lin: High-vegetable and fiber diets increase stool bulk, though a fully prepped colon is typically clean. There may have been small residual fibrous particles visible.

Lin: But normally you you wouldn't make that assumption based on doing a colonoscopy.

Brent: Could you define Irritable Bowel Syndrome (IBS) and explain the gut-brain connection?

Lin: IBS involves recurrent abdominal pain or discomfort linked with changes in bowel habits, such as diarrhea, constipation, or both. Diagnosis is symptom-based rather than through a single biomarker test.

Lin: It is most prevalent in younger adults aged 20 to 40 and decreases in frequency over age 65.

Brent: IBS symptom criteria can sound common to general experiences. Is it recognized as a distinct clinical condition?

Brent: Like I don't know, like sometimes I have a little bit more diarrhea or I'm a little bit more gassy or whatever. Might I get stomach aches a little more and there's not a blood test to to test for it. But you know, people who study it like yourself, I'm sure as you're sure, I'm just no, no, it is very real.

Brent: And it's a very specific thing. And we know it when we see it. Sure, there's not a biomarker that flags it, but it's real. And in this case, I think which is different than chronic fatigue syndrome and long covet, there's a connection to the brain and to mental health, which is very interesting. But is there is that true?

Brent: Is that grouping fair and is there some are there skeptics of it, whether or not it's real?

Lin: Lack of structural evidence does not mean a condition isn't real; many physiological and psychological states cannot be measured anatomically.

Lin: Diagnostic criteria require pain at least one day per week associated with stool changes for six months. IBS affects roughly 4% to 11% of the population.

Lin: IBS belongs to a broader group called disorders of gut-brain interaction (DGBI), which affects up to 40% of people globally and represents a large portion of gastroenterology practice.

Lin: Dysregulation in communication between the brain and the gut can alter bowel function and lead to long-term GI symptoms.

Brent: And then how is it treated?

Lin: Treatment depends on predominant symptoms. Options include dietary changes like the low-FODMAP diet, regular small meals, and avoiding triggers like garlic, onions, or alcohol.

Lin: Over-the-counter options include peppermint oil or laxatives for constipation, along with prescription medications and brain-gut behavioral therapies.

Lin: Therapies like gut-directed hypnotherapy and cognitive behavioral therapy can be very effective for IBS.

Brent: If dietary changes resolve the issue, is it still considered IBS rather than food intolerance?

Lin: If symptoms fully resolve upon removing a specific food, it may be a specific intolerance. However, many patients experience partial relief because an underlying sensitive gut makes processing various foods difficult.

Lin: Diet helps manage load on a sensitive digestive tract while other treatments address broader dysfunction.

Lin: The enteric nervous system in the gut is often referred to as the "second brain."

Lin: Two-way gut-brain communication senses digestion and internal status, sending regulatory signals back and forth that inform hunger or pain.

Brent: Are there specific types of neurons in the gut similar to those found in the brain?

Lin: Nerve terminals in the gut connect through the spinal cord to the brain, which processes signals and transmits feedback along descending pathways.

Lin: It operates as a two-way pathway between the gut and brain.

Brent: What makes the gut's neural connections distinct compared to nerve sensations elsewhere in the body?

Lin: During fetal development, central nervous system cells and gut neural cells originate from shared tissue. Additionally, because the gut interacts extensively with external substances, it features an extensive nerve plexus intertwined with immune defenses.

Lin: You know, that's where it gets into the what's exposed to the outside. And so there's just such a strong nerve plexus to sense because it has to be protect us and our immune system that also communicates to the brain that may be different than other parts of the body.

Brent: Is IBS primarily rooted in altered gut-brain interactions, and can managing stress or psychological factors improve outcomes?

Brent: So but maybe the the cure for lack of a better term is improving mental health. But is that right? Is that what you end up dealing with? You're really you're almost more of a psychologist or a psychiatrist in the way that that you treat this at some point.

Lin: Complex cases benefit from a biopsychosocial approach evaluating biological, psychological, and social factors. Stress and anxiety affect physiological responses across the body, including bowel function.

Lin: IBS is not simply anxiety manifesting as GI issues; many patients with IBS do not have anxiety or depression. However, chronic unpredictable symptoms can increase hypervigilance and amplify pain sensation.

Lin: Did you know? What did I do? Am I going to have a problem? And it becomes you, makes you more hyper vigilant, and then it amplifies the sensations. And so it's harder to engage the pathways from the brain to the gut to kind of suppress that information. So in a way it's protective to you, but in a way it's conveys pathologic with long time.

Lin: Severe symptoms are more frequently associated with comorbidities like chronic fatigue syndrome or fibromyalgia. Early life adversity or chronic stress can increase vulnerability across multiple conditions, but it is one factor among many.

Lin: And then the more you have, the more likely you're going to have these conditions. But that's probably the exception than the rule. A lot of us, including myself, have had adverse childhood experiences, but it doesn't mean I'm going to get IBS.

Brent: So dysregulated gut-brain communication is considered a core factor in these symptoms?

Lin: It is a major contributor. Additionally, an infection like severe food poisoning can trigger post-infectious IBS that persists after the pathogen clears.

Lin: Co-occurring stress during an acute infection increases the likelihood of developing post-infectious IBS. Multiple biological and psychosocial variables intersect.

Brent: Yeah. And these, these infections, it's so clear this is true in Covid. It's true in chronic fatigue syndrome. I'm surprised to hear it's true here that when we get infections, a bunch of things that we don't like can pop up and they can hang around for long periods of time, sometimes for the entirety of our life. So there's definitely a lesson in avoiding infection, if you can.

Brent: I went through this roller coaster on the Covid shot. I was very convinced of it initially, and I thought, I don't need the boosters. And then we did an episode on long Covid and I said, oh, I think the I want the booster because I want to avoid long Covid. I'm not worried about the acute phase itself as a healthy middle aged person, but I sure do not want long Covid.

Brent: I sure do not want chronic fatigue syndrome. And so if you're not convinced of the Covid booster or a flu shot or something, spend some time looking at these issues and you'll become convinced pretty quickly.

Lin: Post-viral GI issues, including post-COVID IBS, can develop following viral infections.

Brent: So so it does. They all are related. They're all in this category of related to infection. We don't totally understand them. They tend to be chronic. The it seems the science is still fairly early on some of these and really understanding what's happening in the body, but it does seem to be systemic. Do we look to something like, are we seeing any improvements, something like psychedelics or, you know, with something like this?

Brent: I think about eastern medicine a little bit more than I do Western medicine. Maybe that's wrong. But, you tell me.

Lin: Patients often seek holistic or integrative approaches. Acupuncture shows benefit for nausea, vomiting, and constipation. Herbal options exist, though clinical trials vary in strength.

Lin: Practices like yoga and mindfulness are beneficial, and research into therapeutics like psychedelics is expanding.

Lin: The goal is matching the right individualized treatment to each patient.

Brent: Yeah. It all comes down to a personalized approach, which is wonderful but very hard to scale. And the health care system is a little, little maxed as it is. Is there a push to put it in the DSM that I'm assuming you would, you would push back against, but is anybody saying, hey, we should be diagnosing this in the same way that we do other mental health issues?

Brent: And that's as of course, you know, but it's the kind of the Bible for diagnosing depression or anxiety and 500 other issues. Is there a push to put IBS in the DSM?

Lin: Rather than formal DSM inclusion, clinicians use multidimensional profiling across clinical factors, quality of life, and psychological impacts to guide care.

Lin: Subtyping patient profiles helps tailor therapy effectively based on unique symptoms and overlap with other health conditions.

Brent: So DSM style categorization, without formally being in the next version of the DSM that comes out every few years.

Lin: Exactly.

Brent: Okay, I can't let you out of here without asking about, GI appliances. So I'm a I'm a big Toto. We're a Toto family. I'm obsessed with the Toto. I can't believe that more American. We don't. There aren't Toto everywhere. The bidet toilets. It's got a warm seat. It dries you, it cools you. So what are your thoughts on?

Brent: Do you have recommendations on toilet paper or what do you think about the the bidet, the Toto style toilets?

Lin: Bidet seats and specialized toilets aid hygiene for GI patients. Targeted water spray can also stimulate local nerve reflexes to assist rectal contraction.

Lin: It provides effective cleansing and helpful stimulation for many patients.

Brent: Yeah, it's very gross and it is TMI. But I think if somebody who doesn't have a Toto, there is a it kind of stimulates the body to get rid of a little remnants. What would be the way that I would describe it? And you just kind of more fully clean and I don't know, it's enjoyable. Like the water is warm and like it feels nice.

Brent: It's just it is a top to bottom, very pleasant experience on toilet paper specifically, do you think is there a like correct way to wipe? Is there a like we should have the four ply. Like is it a dab, is it a you know, I know obviously with with women there's a, there's a, you know, you're going front to back, but I don't know.

Brent: Is there any science on this.

Lin: Wiping front-to-back prevents bacterial spread. Soft paper or pre-moistened wipes reduce irritation from frequent wiping.

Lin: And so probably using something like, more moistened wipes would probably be better.

Brent: Like a baby wipe.

Lin: Yeah. Something more like that because it's less traumatic on the bottom.

Brent: Okay. And then just very final question, what's next? What are you excited about. What's what's coming down the you know, what's in the pipeline in terms of its early and in the research. But it's exciting and promising.

Lin: Microbiome research and personalized health metrics are promising areas. Emerging ingestible capsules can sample fluid, deliver localized medication, or capture images in the small intestine.

Lin: Handheld breath monitors for hydrogen or methane and wearable health devices provide real-time biofeedback on autonomic nervous system function to help anticipate symptom flare-ups.

Lin: Multidisciplinary integrative care combines dietitians, psychologists, and gastroenterologists to manage health comprehensively.

Brent: Wonderful. Well, Doctor Lynn Chang, thank you so much for your work. And thank you so much for your time today.

Lin: Thank you.

Brent: The Life Lab by Death Clock is recorded in Boulder, Colorado, and San Francisco, California, produced by Patrick Gudino, with music by Patrick Lee, and hosted by Brent Franson, founder and CEO of Death Clock.