Anita Rao
Everybody poops, but few people delight in discussing it. I guess the exceptions are if you're the parent of an infant or someone like my dad. He's a gastroenterologist, and for as long as I can remember, it was completely normal to ask questions about how what comes out of my butt helps explain what's going on inside my gut. Growing up, I used to joke with friends that farting around the dinner table was even encouraged in my house. I'm somewhat exaggerating, but we definitely had poop-related artifacts, everywhere. Right next to the front door, there was a wooden plaque celebrating my dad's first patent: a silicone device to help people with constipation practice pooping, or as I call it, the patent for fake poop. My parents have framed cross dishes of toilets hanging up in the living room. My dad has at least 10 or 15 different shirts with colons, poop or gut jokes on them. And even an apron that has an image of the Bristol stool scale. If you've never heard of it, it's this diagnostic chart that classifies the seven different kinds of poop that come out of us from watery to lumpy. So while this topic might make some people turn up their noses, I say: Let's hold our noses and get to know our guts a little bit better.
This is Embodied. I'm Anita Rao. Behind our belly buttons, there is a whole world at work that we take for granted. The gut microbiome is one of the most complex and fascinating systems in our bodies. Think of it as one of the most densely populated habitats on the planet, and we just move around with it every single day. If you like a good wellness fad, then you probably know the craze over gut health is everywhere. Grocery store shelves are lined with probiotics, kombucha and healthy gut tea. But are the promises on product labels real and rooted in research?
Ian Carroll
It's a very, very diverse microbial community. And it's not just bacteria. It's viruses and eucharia, [and] parasites. The microbiome is the cumulative genomes of the microbiota. And we are always talking about the microbiome, because that's how we analyze them through their sequences.
Anita Rao
Ian Carroll is an assistant professor of nutrition at the University of North Carolina at Chapel Hill. He has his own lab on campus where he and his colleagues study all kinds of things related to intestinal microbiota, like digestion and our immune system.
Ian Carroll
We are seeded from birth. There's a little bit of controversy over whether we're exposed to gut microbes in utero. I won't comment on that right now. But essentially, when you're born, you're supposed to be sterile. And then you acquire your microbiota from your mother. Now, whether you're born via C-section or a natural birth, you're going to be colonized by vaginal microbes or skin microbes. And that has a large impact initially on the types of bugs that colonize the infant. Then as you get a little bit older, you change to — about three or four years old — you change to a kind of an adult-type microbiota. And that's what persists through life. And there's a series of ideas and thinking that whatever you're colonized with initially will impact what happens to you later on in life: obesity, umm, inflammatory bowel disease, irritable bowel syndrome, and many other gut-related microbes, or gut-mediated phenotypic changes in human[s].
Anita Rao
My dad is a gastroenterologist, so I grew up learning all about this. And one of the things I remember him saying to us when we were little was: The best thing that I could do for your future health is to kind of expose you to as diverse a range of environments as possible, you know, we should have just kind of sent you all to rural India and had you live there for five years, and you would have had a really healthy gut. So how does the environment that we are surrounded by impact the kinds of bacteria that are growing inside us?
Ian Carroll
It's a really, really cool question. And he was right. Let me just say that. So um, typically what we believe in the field is that a very diverse microbiota is a beneficial microbiota. And there is a drop in diversity — so like, we're not just talking about, you know, abundances, but different types of microbes — so there's a drop in those associated with many intestinal-related diseases: obesity, inflammatory bowel disease and irritable bowel syndrome. So yeah, the more types of microbes that you get into your gut, the healthier it's predicted that you're going to be. And not only that, we've done some studies, which showed that not only is the diversity associated with health, but also mental health. So that's a very interesting area that's being explored at the moment. So there's also this idea that we are missing microbes, because we're so hygienic at the moment, that there are microbes that we used to have and we've lost over time. And those microbes are probably beneficial for us, but they don't exist anymore, particularly in developed countries.
Anita Rao
My dad Satish grew up in India in a very different microbial environment than the one he lives in today. He went to medical school there before eventually making his way to America with a stop along the way for residency and fellowship in the United Kingdom. It was there, he met a lovely woman named Sheila. I call her mom. So, my friends would always joke in high school that in our household, it was fine to fart around the dinner table. And farting was just like [laughs] so okay that was encouraged.
Sheila Rao (Anita's mom)
I don't know about it being encouraged, but it certainly wasn't taboo. I mean, anything GI was, you know, on the table for discussion, and we were very open — from the fake poop when, you know, when you all were small — Dad's patent was on the wall. So it was very evident that anything gastroentestinal was okay.
Anita Rao
Dad, did you want us to grow up with a particular approach to thinking about our gut and poop?
Satish Rao (Anita's dad)
So I think mom echoed it quite well. Essentially, there is no reason to feel embarrassed or ashamed about talking about one's health — any part of the body. And for some unclear reason, the gut takes a major hit when it comes to talking. People usually get too embarrassed to talk about farting or pooping or stool leaking, and so on. Whereas people are never too embarrassed to talk about chest pain or headaches or other body aches and other issues in the body. So I think, you know, some, it is physiological. It is normal for all of us to belch. It is normal for all of us to fart. It is normal for all of us to poop. So these are all normal things that are happening to each and every one of us. Now, some of us will be probably fart in privacy or at other times — when you're walking or whatever — but if the fart is going to come if you're sitting [at] a dining table, then so be it. Its going to happen. It's very hard to control it, and there is no reason to control it. I think you just have to let it go.
Anita Rao
[ Laughs] You don't think people should hold their farts ever...?
Satish Rao (Anita's dad)
There is no reason unless they feel embarrassed to to hold the fart. So you know, it is, I think, perfectly appropriate to excuse yourself and say: Hey — or either you fart and then say — I'm so sorry, you know, you're going to have a smell.
Anita Rao
[Laughs]
Satish Rao (Anita's dad)
And just move on. It can be very uncomfortable. And sometimes if you control it, then you may get pain in the body, because you're pushing the gas back into the gut, and the gut wall will get distended, and there is a fight between the gut wanting to push it out, and you are trying to hold it back. And that can cause discomfort and pain.
Anita Rao
So let it out.
Satish Rao (Anita's dad)
Yep.
Anita Rao
What is your gut mantra?
Sheila Rao (Anita's mom)
Gut mantra? Huh.
Satish Rao (Anita's dad)
Eat healthy. Stay healthy. And poop healthy. That would be my gut mantra.
Sheila Rao (Anita's mom)
Yeah, I think eat healthy. Try to exercise. Try to poop every day.
Anita Rao
Multiple times a day, right?
Sheila Rao (Anita's mom)
Multiple times a day, yeah, when you've got to go, you've got to go!
Anita Rao
Cramping, bloating, bubble guts and other gastrointestinal reactions to what we eat can come on fast and plague us for so long we start to just think they're normal. The pain and discomfort is often not severe enough for us to change our habits or see a doctor. So we just go through life this way. I'm not here to push miracle tea or high-priced yogurt. But there are things that we can do to make our gut microbiomes healthy. Let's go back to the lab of nutrition professor Ian Carroll.
Ian Carroll
Are you aware of germ-free animals?
Anita Rao
Yeah!
Ian Carroll
Okay, so these are animals that are born and raised in this completely sterile environment. And so we're controlling the microbial environment of these animals. So with respect to nutrition and energy, these like germ-free mice will eat more and gain less weight. So that just shows you how much your microbes are contributing to your caloric intake. Now, when you eat something, and your microbes are there, they're just there waiting for food, right? As we get our food, and they are given it. So depending what you're going to eat is going to influence how your microbes behave and the type of microbes that are there. So there was a study done where they had people change from very drastic diets — vegetarian to a carnivore diet — and within 24 hours the microbiota had changed drastically. Now that isn't a typical way of changing your diet. People change their diet in more subtle ways. So generally, if you change your diet, it's going to take ... Your microbiota will change within a week.
Anita Rao
So we know that many people Ian call the gut our "second brain." How true is this metaphor?
Ian Carroll
Quite true.
Anita Rao
[Laughs]
Ian Carroll
I would say that there's a lot of interesting research that has shown that that could be true. And we still need to know a little bit more about how this happens and how big an effect it has on us. I think the most convincing research is in like what they call preclinical trials, which is usually mouse work. Again, we talked about germ-free animals earlier on. And germ-free animals actually have a higher stress response, but are less anxious, but when you colonize them with a normal microbiota, how they should be existing, that normalizes. Your stress response goes down and your anxiety increases.
Anita Rao
Well, tell me more about that because there was a really transformative study looking at mice that really kind of helped blow up this field of brain-gut connection.
Ian Carroll
Yeah, so one of my colleagues and friends John Cryan, many years ago — it was I think it might have been in 2005 — he took a mouse, and gave it a stress test and found that there was a certain level of depression, okay. And then gave it a probiotic, which I guess maybe it isn't a probiotic, it was a microbe — Lactobacillus strain — and gave it this probiotic and reduced the depression levels in that mouse, in that group of mice. Then he cut the vagus nerve — now the vagus nerve connects your gut to your brain — and again gave the microbes and lost that antidepressant influence on them. So there is a suggestion that microbes can influence how you behave. Your levels of depression maybe anxiety, and that the communication goes from your gut to your brain via your vegas nerve.
Anita Rao
Turns out gut feeling is more than an idiom we use to describe our intuition. It is a real thing. Our gut is intricately tied to other systems and organs in our body. And that includes the big one at the top: our brain. Dr. Lin Chang has studied that link for a long time. She's a professor of medicine and vice chief at the Division of Digestive Diseases at UCLA.
Lin Chang
You know, we use that term gut feeling, my gut instinct, and it really comes from a certain place. So ... there are metabolites that you've heard from Dr. Carroll that the bacteria make, but also the lining and the bowel itself has certain hormones, like serotonin is one of the big ones. And these types of substances can pass into the blood and go to the brain. And so I think that how we're feeling in the gut, maybe sometimes we're not even always consciously aware of it, but then we can kind of sense it. So some of the information we're not — it doesn't always go to the certain parts of the brain that we're consciously aware of it — but we can feel it maybe in the like brainstem regions, or what we call the sub-cortical cortex regions. And then the way that the brain can signal back to the gut, maybe we're not even aware of that. So a lot of what goes on our gut, we're not even consciously aware of it, which is a good thing.
Anita Rao
Well, how about stress? Because I feel like you know, there are, there are obvious times when you can sense, you know, you're getting ready for a big presentation and you start to feel, you know, funny sensations in your stomach, or you may have loose stool, or you may feel like you're gonna throw up. So that kind of signals a really clear relationship between stress and the gut. Can you talk a bit more about what we've understood about the extent of this stress-gut relationship?
Lin Chang
Yeah, I mean, stress and its effect on the gut has been studied in animal models like you've heard and also in humans. But we all are basically hardwired to have a certain type of gut response to stress, most of us are. And a lot of that is mediated through nerves, but also this particular hormone that can communicate between nerves, and to the gut, called corticotropin releasing factor or CRF. And so when we are under stress — and there's an acute response to stress, and there's a chronic response to stress — if we have chronic stress that's different than if we had acute stress, and we're running away from some threat. But what it does in the gut, typically, is in the upper gut it will actually slow stomach emptying, and people tend to have nausea, and they can even have vomiting. So you've probably heard of scenarios where someone's going to perform, or it's before a big game, and they vomit. So that is due to a stress response in the gut. In the lower gut, the stress tends to do something different. It makes you have frequent bowel movements, even diarrhea. So in a way, I think about it as when we're under stress, the gut is actually getting rid of contents from both ends. And maybe that's protective at that time.
Anita Rao
Learning about the intricate relationship between our gut microbiome and our minds has been a fascinating experience. But when that brain-gut connection gets really off track, is it possible to get it back to a good place? I asked nutrition expert Ian Carroll about an option for folks who suffer from severe recurring symptoms of a bacterial imbalance in the gut. And what he told me goes way beyond popping probiotics.
Ian Carroll
So my primary research is on anorexia nervosa. It's a very important illness. It affects 1% of the U.S. population, and even though there's an established pipeline for this treatment, it still has the highest mortality rate of any psychiatric disorder, so there's a desperate need for new treatments. So the reason why we're looking at the intestinal microbiota and anorexia nervosa is because there's weight dysregulation, and there's behavioral dysregulation. And we know that both of those things are associated with the intestinal microbiota. And we don't believe that the intestinal microbiota causes the illness. But after depriving yourself in nutrients for so long, you could end up with a composition of microbes that are going to influence how [with] the food that comes in, whether it's going to metabolize them appropriately. And it's also going to maybe increase your stress response or your anxiety. So then we get on to fecal microbiota transplants, okay. This is a technique that comes from ancient China, and it was called yellow soup. So I hope nobody's having soup for lunch right now.
Anita Rao
[Laughs]
Ian Carroll
And it was fermented camel feces or infant feces, and it was consumed to treat numerous types of illnesses, and what it's primarily indicated for right now is Clostridium difficile infection, so a recurrent infection. You can't get rid of Clostridium difficile in humans, and it is causing a lot of diarrhea. It's causing inflammation. And it's very, very nasty. You take one FMT...
Anita Rao
FMT is...?
Ian Carroll
Sorry FMT is a fecal microbiota transplant. And 90% of people are ultimately cured. It goes up to about 95% after two rounds of FMT. And this is really, really effective.
Anita Rao
So basically, what's happening is we are taking a sample of fecal matter from someone with a healthy gut and we are implanting it into someone who has things going on in their microbiome that are abnormal.
Ian Carroll
So if you take C. diff infection, for example, it's bloomed, and it's taken over the ecosystem of the gut, and that's why it's causing all the trouble. But if you put back in a normal microbiota from a healthy individual and reestablish a healthy ecosystem, you go back to normal.
Anita Rao
Our excrement is one of the best ways to learn about how to make our gut microbiome a healthy environment. And studying the poop of other species has helped clue researchers in more about humans. Lydia Greene is a postdoctoral fellow at the Duke Lemur Center, and she says the lemur is a near perfect animal for better understanding human gut health.
Lydia Greene
Lemurs are a fascinating system for studies of the gut microbiome, gut microbiota. They're primates. So they are closely related to us, but they're our most distant cousin. Lemurs are also critically endangered. They're one of the most endangered vertebrate groups on Earth. So we know the microbiome relates to health. We know it relates to nutrition. And so the more we learn about the microbiome, the more we can use this field as a tool to help improve lemur ecology and lemur health overall. My particular passion is the folivores, the leaf-eating lemurs and understanding how the interplay between eating a really tough diet — tough in terms of fiber — how that relates to the microbiome that these animals have and how the microbiome in turn helps these animals digest these tough diets and meet their nutritional requirements under myriad conditions. So a lot of fibers in diets, and especially in plant matter, we think as being something called recalcitrant fibers, and cellulose being the classic one of these.
Mammals, like humans, don't have the enzymes to break down cellulose on our own. We can't do it. And so without our microbes, it would just pass through our gut, and we would poop it out intact. But microbes are really, really good, especially the microbes in the gut, are really good at the metabolism of fiber, and they do it under anaerobic conditions. So in the absence of oxygen, it's called fermentation. And so these microbes break down — they ferment your fibers for you, and the microbial byproduct, so the excrement of the microbes are actually nutrients for the animals. So those nutrients are called short-chain fatty acids. And so microbes take your fiber. They eat it for you. They make short-chain fatty acids. You the animal absorbs those short-chain fatty acids, and those help you meet your energetic demands, and they also help promote health in a variety of body organs. So if we can understand what goes on in lemur poop as well as monkey poop, as well as ape poop, as well as human poop, that provides clues about our own evolutionary history with our gut microbes.
Anita Rao
My gut tells me we've come to the end of this installment of our show. But I'm going to keep thinking about how our gastrointestinal system ties it all together, and I hope you will too. My thanks to Grant Holub-Moorman and Charlie Shelton-Ormond for producing this episode. Jenni Lawson is our sound engineer, and Lindsey Foster-Thomas is our executive producer and content director. Our theme music is by Quilla.
Embodied is a production of North Carolina Public Radio WUNC. Thanks also to you for your support of WUNC and to Weaver Street Market, a worker and consumer owned cooperative selling organic and local food at four Triangle locations. Now featuring online shopping with next day pickup: weaverstreetmarket.coop. I'm Anita Rao on an exploration of our brains, our bodies and taking on the taboo with you.
