INTRO
I have to tell you something before we get into this. I spent years struggling with my gut. Bloating, food reactions, food babies, a candida overgrowth that kept coming back no matter what I threw at it. And I threw a lot at it: probiotic after probiotic, protocol after protocol, always looking for the one thing that would finally fix it.
What actually ended up working wasn’t what I expected. It wasn’t a probiotic or a supplement at all. It was supporting my digestion first, and only after starting that work, expanding my diet to include more diversity: real plant foods and fiber, and then adding fermented foods. Once I did it that way, the candida cleared up and stayed gone. That order of operations turns out to matter a lot, and it’s actually backed by some very cool research that Kara and I both love, a study out of Stanford on fiber versus fermented foods that we are going to get into today.
That is precisely why I am so excited to introduce you today to Kara Siedman. Kara is a registered dietitian, certified diabetes care and education specialist, and VP of Science and Partnerships at resbiotic. She has over 15 years of clinical experience across inpatient care, outpatient program development, and integrative and functional nutrition, and her path into this world started in a leading gastroenterology practice, where she began weaving root-cause approaches into GI care. That shift turned into a full specialty in the gut microbiome, and it has led her to work alongside some of the top biotech and microbiome-focused companies in the space.
What I love most about Kara is how she talks about the science. At resbiotic, her job is basically translation, taking complex, dense microbiome research and making it something healthcare providers, and now you, can actually use. She brings clarity and credibility to a topic that gets muddied by marketing all the time. We have all been on those Instagram ads. And today we are going to get into exactly that: what the microbiome actually has to do with your hormones and your perimenopause symptoms, how to evaluate whether a microbiome supplement is worth your money, and the real difference between the types of gut support out there.
I am so glad that you are here, and I can’t wait for you to nerd out on everything that Kara shares with us today. Kara, welcome to Mornings with Megan.
Kara: Thank you so much for having me. And you used my favorite word, nerd, because I always like to say that I’m a nerd with a capital RD.
Megan: That’s so good with your credentials. Amazing.
Kara: Yeah.
Megan: Well, as a nerd joke, I wish I had something to deliver there, but maybe we can put our nerd hats on and bring everyone in with us with some basic information, because I feel like the definitions alone are so confusing. Are we talking postbiotics, prebiotics… wait, there’s not a peribiotic? That’s perimenopause. But can you give us some definitions so we’re all in the same starting spot to talk about this?
Kara: I think it’s important, because there are a lot of these terms we use interchangeably, like microbiome. I was talking to someone recently who asked, well, what do you mean by gut, is that just your stomach? So I think even from an anatomical perspective there’s confusion. We have our digestive tract, which runs mouth all the way through anus. You have your stomach, your small intestine, your large intestine. But the microbiome is basically this collection of microorganisms, from bacteria to fungi and viruses, that live in very specific areas throughout the body. We have microbiomes throughout our entire body: our gut microbiome, which is in your colon, is your most dense microbiome, your largest microbiome. It’s the microbiome we talk most about when we’re talking about the gut. So when we think about prebiotics, probiotics, postbiotics, we’re really thinking about the gut microbiome. But every part has one. We have a lung microbiome, an eye microbiome, an estrobolome, which we’ll talk so much about, my favorite word. And basically what we’ve come to learn over the last 20, really the last 15 years, microbiome science has just exploded. I didn’t learn about it when I was in school. I got into the microbiome at a very young age without even understanding what the microbiome was, because I got into fermentation. That’s a whole other story we can talk about.
Megan: Ho ho, were you making sauerkraut in your mom’s kitchen?
Kara: This was all when I went to college and I wasn’t even a nutrition student yet, I was pre-med, still trying to figure out what I wanted to do. I got very much into fermentation and sprouting, and my college dorm, and then my apartment, was basically a science experiment. I got my own apartment very early on as an introverted extrovert who needed control over quiet space, and my kitchen was fermenting everything. It’s pretty interesting that my career path led me to actually studying and working so deeply within the microbiome. We’ll talk a lot about fermented foods because I’m a huge fan. But the gut microbiome, we’ve really come to learn so much about. It governs so much of our health, it acts as this gateway to the rest of the body. We often think of the body in silos, cardiology and neurology and endocrinology, but the microbiome really acts as that center, that gateway, that foundation connecting all these systems. So for me, it’s become such a predominant focus in my career as a dietitian, in how I work with clients, but also in my professional path.
Your prebiotics are essentially your food, the fertilizer for growth. They come from the diet, it’s what feeds your beneficial bacteria. Think of this as your fibers, traditionally a lot of carbohydrate foods, fruits, certain vegetables, nuts and seeds. But then you have things like resistant starches and omega-3 fatty acids, which most people don’t even think of as prebiotics.
Megan: I would not have thought of that as a prebiotic. I’m just like, well, it’s in my fish.
Kara: There’s actually been quite a bit of research on this. You have some of these emerging prebiotics, polyphenols, which are non-carbohydrate. Think of the color of blueberries, those anthocyanins, your pomegranate, all those bright colors we talk so much about. What’s important is that many of us just lack this in the diet. We know 97% of Americans don’t consume enough fiber in general, which means we’re not eating enough of these prebiotics, let alone the diversity. Prebiotics are specifically utilized by your bacteria, so not all carbohydrates are prebiotics, they have to be consumed by your bacteria to produce beneficial compounds. Think green bananas, onions, garlic, I’m sure you’ve talked a lot about FODMAPs, and that might be a term. These are very specific types of fermentable carbohydrates. This comes from the diet, they’re not live microorganisms, it’s the fertilizer for growth.
Then you have your probiotics, which are of course live microorganisms, what most people traditionally think of. These are your friendly neighbors, I’ll talk a lot about the neighborhood, these are the neighbors you want to live next door to, the types you want predominantly living in your neighborhood, and they have very beneficial functions. They carry out specific functions within the microbiome, from metabolic health to hormone health to brain health. The problem is, because of the way we live, our diet, medications, the air we breathe, our friendly neighbors become disrupted. That’s why probiotics have become such a supplement, and in fact are often needed.
Postbiotics is this whole new category. In 2021 the definition expanded to what we understand it as today: beneficial compounds or byproducts that your probiotics produce, butyrate being a very common one, known as a short-chain fatty acid. But we’re also starting to understand what happens when we purposefully heat treat or heat-inactivate, so we kill it, in a sense. I think of postbiotics as ghost biotics. If you think of a ghost, it hasn’t quite fully crossed over to the other side, but I can’t see the ghost around me, and if it came behind me and knocked something off my printer, it’s intentional, it wants to do it. That is a postbiotic. It’s basically a dead probiotic, but it retains very specific functions and benefits. Probiotics have to travel to their destination and then start doing all the important jobs they do. Postbiotics don’t have to travel, they just get to their destination. And that’s a very exciting thing.
Megan: I have follow-up questions, because one of the big conversations when you’re thinking about a probiotic is everyone’s always talking about the delivery mechanism. Can it stay alive in the factory, does it stay alive, does it die before it gets through your stomach acid all the way down there? So the benefit of the postbiotic is that it’s already dead, dead on arrival, we’re not worried. But then my question is, what is the difference between my probiotic that died in the back of the Amazon truck and intentionally heat treating and killing off a probiotic?
Kara: Yeah, so we’re using these specific strains, and strains are important to understand, because basically what we’ve come to understand about probiotics is strain specificity. That’s a big term a lot of us don’t understand. I use the analogy of dogs: all canines are part of the same species, canine, or even humans, we’re all Homo sapiens, all part of the same species. But when you get down to the specific canine, a pit bull or a West Highland Terrier or a Yorkshire Terrier, genetically they’re different, they look different, they act different. That’s the same with our bacteria. You can have a specific Lactobacillus acidophilus species, very common, we find it in yogurt, but when you get down to that very specific strain, say LA5 or LA14, they function very differently, they have different jobs, they’re different dogs. One’s a West Highland Terrier, one’s a pit bull. What we’ve really started to understand as technology has advanced are those very specific functions and benefits that these specific probiotics have. What’s fascinating is when you heat treat or kill these into postbiotics, some of those functions get retained, but it’s not the same thing, so unless you study it specifically, you don’t know. You could take a specific bifidobacterium strain and kill it, and it could not do anything, that wouldn’t be a good postbiotic. Whereas if we purposely heat treat or inactivate it, we’re actually looking at the very specific functions being carried out, which means you’ve got this biotic with very targeted benefits that doesn’t need to be alive to get the benefits. You have stability, it doesn’t matter what’s happening in that hot Amazon truck, doesn’t matter what’s happening in your digestive tract, you get consistent dosing. If you take a probiotic and say well, it doesn’t matter, a bunch of it’s dead, I’m still getting benefits, you don’t actually know that, and are you getting a sufficient dose? Which is why the science and research become so important.
Megan: Of course. I feel like we all want all the research and all the testing and we don’t realize how little of it is actually out there. So if you’re taking all these fun strains, studying them, and then killing them off to make our ghost biotics, and then sending them places, is it like they retain the instruction set? Is that what’s happening? It’s like we put them to sleep, here’s your instruction set, and they go carry on in the microbiome.
Kara: Yeah, absolutely. If we say, okay, this specific heat-treated postbiotic L. plantarum specifically supports the natural production of, say, GLP-1, we’ve specifically studied that, and that means you’re getting that very specific benefit. It doesn’t mean it doesn’t have other benefits, which it probably does, but unless you do the science and the work, you can’t say that all probiotics do X, Y, and Z, because they don’t, they do different things. And the more confusing part of this whole conversation is that a lot of research is starting to want to dissect whether probiotics are really only beneficial because of their postbiotics. Because when you take a probiotic, they’re not colonizing. A lot of people say, I don’t have these bacteria, I need to take this so my microbiome has it, but it doesn’t actually colonize. Probiotics are tourists, they’re coming, it’s like an Airbnb, you come in, you enjoy it, and then you leave. We don’t really know why things engraft or colonize, we don’t have that knowledge yet.
Megan: Right, so thinking about neighborhoods and who’s taking up residence makes me think of that Stanford study that you shared. One of the things they talked about was that eating more fiber doesn’t expand the diversity of the neighborhood, eating more fiber just makes more houses in the same neighborhood, more people in the same neighborhood, and it’s the fermented products that are actually changing the diversity, but it’s not being populated with the microbes from the fermented products, it’s like they’re feeding other things that are maybe somewhere else and we don’t know.
Kara: Yeah, and we’ve seen that even in other postbiotic studies, where you take a specific heat-treated strain and it promotes the abundance of others, it’s like, hey, this is a great neighborhood, I’m going to invite all my friendly neighbors, all my cool friends, to come move in. I think where fiber really comes in is that it’s going to feed what’s already there. A lot of people will do stool testing, microbiome testing, and go, my goodness, I don’t have X, Y, and Z strain, but a lot of times they’re actually there, they just might be on life support. If they’re on life support, fiber is going to feed that strain, and that’s why fiber diversity is so important, because different fibers feed different bacteria. Now we still have a lot to learn, we’re kind of at the tip of the iceberg. If you’re taking certain strains and feeding them the right food, and your neighborhood is conducive for it, will you start to increase that abundance? Potentially. There’s also newer research trying to break down what a healthy microbiome actually looks like. We don’t fully know who’s in the neighborhood, what we know is there are characteristics of the neighborhood we want to move into, and there’s this question now of whether diversity is even necessary. It’s coming down to function. Is your neighborhood carrying out the necessary jobs and thriving like a neighborhood should? Is your microbiome performing the functions we’ll talk about around menopause and hormone metabolism efficiently?
Megan: There’s so many bacteria, how do we even categorize all these things? I know you shared some research on the HAC index.
Kara: The index of health-associated core keystone species, which is fascinating, it was something like forty thousand microbiomes.
Megan: Forty thousand samples, and I think they came up with two hundred and one taxa, and they ranked them based on prevalence amongst cross-populations, whether there was a community association with a healthy person and whether it was resilient. But even within that space of two hundred and one species, it seems like we know so little.
Kara: Yep. We know so little. I was in school when we were just starting to touch on this, and all the rage was figuring out which probiotics we’re going to use, which strains, which brands. It sounds like now it’s almost a full one-eighty, where we’re realizing maybe that’s not the way we should be doing things anymore. Especially early on we’ve looked at the microbiome in this conventional lens, I call it the point-and-shoot method: kill this, give this. But it’s an ecosystem. If I look out in my backyard and chop down a tree that a specific plant or insect needed, there’s going to be a cascading effect, and it’s the same in our microbiome. We’ve got friendly neighbors, unfriendly neighbors, but we want the neighborhood to thrive, we don’t want houses crumbling because it changes the look of the neighborhood. If we start thinking in this ecosystem lens, we understand a little more how to use the microbiome to achieve better health outcomes. What’s fascinating now is specific strains for specific needs versus you need this one bug. A lot of microbiome research is trying to discern the signature of a healthy microbiome, you have to have this strain and this amount, or these keystone strains, these influential strains. What that study did was say, well, depending on what you’re dealing with: if you have metabolic disease and you’re missing certain strains, that might be an issue, that might be a need for a probiotic. But if you don’t have that strain and you’re not dealing with any metabolic outcomes, who’s to say you actually need it? I think that’s really the takeaway, that it’s coming down to function. If you’re someone struggling with metabolic changes, or you’re going through perimenopause, there may be very specific strains, whether you have them or not, that are necessary because you need that function supported. So I think what we’re seeing now in the microbiome research space is less about this specific bug and more about what that bug is doing.
Megan: Right, and then supporting some sort of growth, or maybe resonance, of that bug or strain for that functionality. So potentially there could be multiple strains that do this thing and we just don’t know what they are yet.
Kara: Yeah, exactly, there’s still a lot we don’t know, so many uncharacterized strains. I think that’s what makes the space exciting but also confusing. As a consumer, as a patient, some of the marketing I think gets in the way, we sometimes hype up certain keystone strains, like this is part of a healthy microbiome and you must take it, versus, well, what if you had antibiotics and now have diarrhea, maybe you actually need this product. I think it’s challenging providers and healthcare practitioners to think of how we use the microbiome in clinical practice a little differently, versus it being, well, you need this exact strain. It might be, well, you need this strain because we know it really supports antibiotic-associated diarrhea.
Megan: Well, and I think that touches on the whole idea of labeling everything good versus bad, because we also have a lot of information showing that a healthy microbiome actually does have some E. coli in it, or a little spot of C. diff in it. It’s not that C. diff is bad, it’s that within the ecosystem, at the right amount, it’s fine, it’s supportive in some way, or we don’t know if it’s supportive, it’s just not doing anything wrong. But if it overgrows and takes over the entire neighborhood, then we have problems.
Kara: Exactly. I could be living next door to E. coli right now, their yard’s a bit of a mess, maybe they’re a little loud at times, what I don’t want is for them to invite more of their E. coli friends to move into these empty houses. But they’re fine, if I go over and ask for eggs, they’ll actually give me some, which is great, but there’s potential for them to take over, and that’s the thing about our microbiome. There are pathobionts, there are opportunists, and you can have good bugs that turn bad, that’s the other side of it. Even an overgrowth, an abundance of something that’s usually healthy, isn’t necessarily a good thing, because it’s an ecosystem, it’s about balance. The microbiome is Goldilocks, not too hot, not too cold.
CLOSE
That is such a good place to pause for today. We covered the real definitions of pre, pro, and postbiotics, why a probiotic dying in a hot delivery truck isn’t the same as an intentionally heat-inactivated postbiotic, what strain specificity actually means, and the Stanford research on fiber versus fermented foods that’s reshaping how we think about gut diversity. We also got into the health-associated core keystone species research, and why the real question isn’t which single bug you need, but what job your gut needs done.
Next Wednesday, Kara is back for part two, and this is where it gets really exciting. We’re getting into the science behind how a company like resbiotic actually validates what’s in its products, and how all of this connects specifically to perimenopause and your hormones. Thank you for being here with us this morning. I will see you next Wednesday for part two.
