The Gut Health Podcast

Fermented Foods for Gut Health: Myths vs Science

• Kate Scarlata and Megan Riehl • Episode 20

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Fermented foods offer surprising health benefits with science showing they can increase gut microbial diversity in ways other dietary interventions cannot.

• Expert Elisa Caffrey clarifies what qualifies as fermented food: substrate + microbes + time
• While touted as a source of probiotics, most fermented foods don't technically contain probiotics, which require specific strain characterization and known health benefits
•Different types of fermentation are used in food production: lactic acid bacteria ferment carbohydrates in sauerkraut and yogurt; acetic acid bacteria oxidize ethanol into acetic acid in kombucha; and filamentous fungi such as Aspergillus oryzae and Rhizopus species are involved in the fermentation of miso and tempeh, respectively.
• Fermented foods may benefit gut health through microbial derived metabolites rather than just the microbes in the food or beverage.
• Consider starting with yogurt if you are a newcomer and have fun exploring kimchi, sauerkraut and other options for fermented food variety.
• Most fermented foods are safe, though some considerations exist for those with histamine intolerance or sodium restrictions
• Variety is key – consuming diverse fermented foods appears to help maximize potential benefits
• The fermentation process may have mental health benefits beyond nutrition though more research is needed

Try incorporating fermented foods gradually into your diet and experiment with different types to find what works for your body and taste preferences.

 Let us know what makes your taste buds (and gut) happy! 

This episode has been sponsored by Activia. Check out their Gut Health Tool Kit here and A Gut Friendly Meal plan here.

References:

Caffrey EB et al. Unpacking food fermentation: Clinically relevant tools for fermented food identification and consumption

Gaudiest G et al. Microbial and metabolic characterization of organic artisanal sauerkraut fermentation and study of gut health-promoting properties of sauerkraut brine

Wastyk HC et al. Gut microbiota-targeted diets modulate human immune status (high fiber vs fermented food study)

Nielson ES et al. Lacto-fermented sauerkraut improves symptoms in IBS patients independent of product pasteurisation - A pilot study  

Learn more about Kate and Dr. Riehl:

Website: www.katescarlata.com and www.drriehl.com
Instagram: @katescarlata @drriehl and @theguthealthpodcast

Order Kate and Dr. Riehl's book, Mind Your Gut: The Science-Based, Whole-body Guide to Living Well with IBS.

The information included in this podcast is not a substitute for professional medical advice, examination, diagnosis or treatment. Always seek the advice of your physician or other qualified health care provider before starting any new treatment or making changes to existing treatment.

Kate Scarlata, MPH, RD:

This podcast has been sponsored by Activia. Maintaining a healthy gut is key for overall physical and mental well-being. Whether you're a health-conscious advocate, an individual navigating the complexities of living with GI issues, or a healthcare provider, you are in the right place. The Gut Health Podcast will empower you with a fascinating scientific connection between your brain, food and the gut. Come join us. We welcome you.

Dr. Megan Riehl:

Hello friends, and welcome to The Gut Health Podcast, where we talk about all things related to your gut and well-being. We are your hosts. I'm Dr Megan Riehl, a GI psychologist.

Kate Scarlata, MPH, RD:

And I'm Kate Scarlata, a GI dietitian. I'm super excited for today's topic and guest. We will be talking about fermented foods for gut health myths versus science. Our guest today is EliSa Caffrey. She's a PhD candidate in the Sonnenberg Lab in the Department of Microbiology and Immunology at Stanford University School of Medicine. Her research explores the interplay between fermented foods, microbial communities and human health, with a focus on characterizing the metabolites produced during fermentation. She holds a master's degree in bioinformatics from John Hopkins University and has prior experience in biotech research focusing on gut endocrinology. Aliza recently co-led the Fermentation and Health Speaker Series with David Zilber and Dr Justin Sonnenberg and is the founder of Rotten Menu, a platform dedicated to demystifying fermentation microbiology. She has an excellent paper in Advances in Nutrition that she is the lead author on, titled Unpacking Food Fermentation Clinically Relevant Tools for Fermented Food Identification and identification and consumption, which reviews the state of state on food fermentation metabolites and health benefits. We will link this in our show notes. Welcome, Elisa. Thank you so much.

Dr. Megan Riehl:

I'm very excited to be here. I mean fermented foods. We're going to go beyond just sauerkraut. I'm going to learn a lot this episode and it's always fun to really dive into different ways that different things can impact our gut health. So, Elisa, we like to start with a myth buster and, as we kick things off, what myth would you like to bust pertaining to fermented foods and gut health?

Elisa Caffrey:

So I would say that a food that contains microbes does not mean that it is fermented would be my myth that I would like to bust, and a lot of that comes from the way in which we see fermented foods in grocery stores. Now, when we talk about things like gut health and fermented foods, the landscape has gotten very confusing.

Dr. Megan Riehl:

And so trying to really understand what are foods that are fermented and what are foods that might contain probiotics and what are foods that might just have that people hear, you know, just using, like sauerkraut. And we've talked about kimchi and we've talked about some of the literature around these foods and our gut health. But we're going to dive deeper this episode and really learn some of the science and also just some key takeaways on what we're looking for at the grocery store if we want to explore this aspect of health Absolutely, and I definitely think there's just a lot of misconceptions in this area, so I'm excited to have an expert that really understands it.

Kate Scarlata, MPH, RD:

So let's start with just a very like elevator pitch about the gut microbiome. What are some of the terms we need to know when we're thinking about, what are we looking at? Are we looking at the type of microbes in there? Are we looking at what they're making, or the metabolome or metagenomics, or those big terms that you use probably regularly? This will really set our stage today for really having a baseline as we get into the science of fermented foods.

Elisa Caffrey:

When we think of the gut microbiome, we're talking about the microorganisms that live in the large intestine, and so that could include largely bacteria, but also we have fungi, we have yeast, we have a lot of viruses in there. That's been really exciting, and when we are studying the gut microbiome community, we really are interested in what microbes are present and at what abundance, and so that's generally when we're looking at characterizing the gut microbiome. When people go and get their gut microbiome tested, that's what they're looking at ways of doing that. We can do it in kind of a broader view, which is a technique called 16S amplicon sequencing and that just looks at a certain region of a gene that is shared between microbes of the same genus, and the genus is just a way of taxonomically defining different microbes. But if we zoom out, the way that I like to think of what a genus is, is that dogs, wolves, coyotes are all part of the same genus.

Elisa Caffrey:

When we think of a species level, which is what we can do with other methods like metagenomic sequencing, that is when you actually get to dogs are part of one species and wolves are part of another species, and so we're able to get at a deeper understanding of what these different species actually are in the gut.

Elisa Caffrey:

Then there's another level, which is strain level, which has been kind of the latest, very exciting way of thinking about our gut microbiome, and in that case we could really compare it to dog breeds, for example, and that is microbes that have an identity of 99.999 percent. And so that's when we can actually track strains that might be from a mother to a child or, in the case of fermented foods, from the environment to the cabbage itself to say what am I actually consuming. And so we have a lot of kind of different techniques, but I think in the you recent years, we've been able to get really detailed in terms of really mapping out this very specific strain, which might produce different chemicals compared to another strain of the same species that are closely related, but it might have a very different impact on health.

Dr. Megan Riehl:

So interesting. It's always helpful to have kind of these metaphors, to take a concept that you know for all of our listeners. If you're like okay, wait, I'm following the genus and the species and the okay, I'm trying. You know you might have to listen to this a couple of times, but it really helps to understand a very complex topic. So the way you just talked about this was, I mean, so eloquent and obviously, like you are the expert in this space and we don't have to know all of the details of what you're saying, but you're highlighting that it does take a lot of thinking through to understand this.

Elisa Caffrey:

Totally. I mean, the way that we really have thought about the gut microbiome for a while was really just based on this kind of broad genus idea which, if you think of it in terms of coyotes and dogs and wolves all being in the same genus, it was so broad and so now we're finally able to get to a level. That's been really, really helpful. And the other kind of thing is, once we get to the species level, we can really start looking at diversity or richness, which has been a really important metric for thinking about the gut microbiome and health. And so, in terms of you know, people have studied a number of different ways in which we want to characterize or understand what a healthy gut is.

Elisa Caffrey:

But as of now, I think the kind of best metric is that a more diverse microbiome makes for a healthier gut, and we really see that in terms of the way that people might respond to certain treatments and drugs, that the more diverse your gut is, the better the response In terms of risk of certain diseases.

Elisa Caffrey:

Again, the more diverse your gut is, the better your response and the less likely you are to have certain of these especially non-communicable diseases. And what has been really exciting about kind of connecting this back to fermented foods was that there was a study done a few years ago now that was one of the first to really show a dietary intervention, which was a fermented food diet increased gut microbiome diversity, which is something that we really hadn't ever been able to do, where you can change the way in which your gut microbiome might consume, look at certain fibers and produce different metabolites and have a different response. But really increasing the diversity hasn't been shown before, and so when we think of consuming food in order to impact the microbiome, it seems like fermented foods have been really successful in having this positive effect.

Dr. Megan Riehl:

So what qualifies as a fermented food or beverage? As we think about how do we diversify our gut microbiome, tell us some of the qualifications of that.

Elisa Caffrey:

When we think of fermented foods, we really can abstract it out to. You have a substrate, which could be fiber, like a cabbage or milk, If you have dairy. We have the microbes, and then we have time, and so what we really are trying to get at is any sort of food. Where we have, we're giving the microbes the food for them to consume and enough time to produce some sort of chemical that might impact flavor. It's going to impact preservation of the food and, as we're understanding, it's going to impact the health of the person consuming it, and there are a number of different foods. I mean, I don't think there's a single group around the world that does not have some sort of food in their diet that is fermented in some way or, especially if you think of pre-refrigeration. Microbes are consuming and having an impact on that food in some way, shape or form, and we can break this down either by substrate. So thinking of things like, again, vegetable ferments we have kimchi, we have sauerkraut, we have gundruk, we have a ton of different things Dairy we have kefir, we have yogurt, we have cheese.

Elisa Caffrey:

But even getting to fruit right, Like wine, is technically a fermented food. We have vinegar, even just using sugar. So for kombucha, we have tea and sugar as kind of a base for the fermentation. Meat ferments right, Like certain types of sausage used to be fermented. So we really, I mean you can ferment anything right Like, as long as it's the raw ingredient is accessible to the microbe and you create an environment for that microbe to want to consume. So that could be regulating temperature, regulating the amount of salt. You can get fermentation to happen, which you also see a lot in kind of fine dining now with the rise of fermentation. They're trying to ferment, you know, waste products even in order to get some really cool flavor profile to come out.

Dr. Megan Riehl:

I've seen some top chefs that you know they'll talk about their fermented foods that they'll bring on for a challenge or something, and I hear what you're saying. Yeah, totally.

Kate Scarlata, MPH, RD:

So I'd like to talk a little bit about fermented foods. Everywhere on TikTok, everywhere on social media, it's like have more fermented foods. They're a source of probiotics and you know, probiotics has a specific definition and this just can sometimes be the case that they are, and sometimes maybe not. Can you elaborate a little bit on fermented foods and are they all a source of probiotics or what do we know?

Elisa Caffrey:

I'll actually take a step back and just say, talking about these different substrates, there are different ways in which you can actually then get the microbes to start the fermentation, or where are these microbes coming from? And in certain cases, like in vegetable ferments, we have wild fermentation, which is just microbes from the environment start fermenting and just turns out work incredibly well to make some sort of sauerkraut. We have what's also called like a backslop method, which might be used a lot in sourdough production, where you have like an old batch and it's a community that's fairly stable, but we haven't really characterized it and you can put it in. And then we have examples, like in yogurt, where we're going to pasteurize the milk and then add in a strain that has been usually pretty well studied, and that's an example of a microbe that is both going to be well studied for fermentation but also for the probiotic potential. And so probiotics really are according to the WHO. They have a definition they're these live microorganisms that when you administer them in adequate amounts they have some sort of health benefit, and so they really have to be well characterized.

Elisa Caffrey:

The ISCPP, which is this international research group, International Scientific Association for Probiotics and Prebiotics, has gone a step beyond that and said they also need to be defined at a strain level. You need to have the genome sequence. So we really have to deeply characterize these microbes in order to say that they are probiotics and we also need to really understand what is the specific benefit that they're giving to the host. And so there's been this kind of split between probiotics that we have studied and very well characterized and then these studies looking at consumption of fermented foods saying we see a benefit, but most fermented foods don't actually have well-defined probiotic strains. We just know that there's some benefit to consuming these microbes that are established in these food communities, basically.

Elisa Caffrey:

And so the short answer is most fermented foods are not probiotic unless there are very specific examples. Usually it's dairy ferments, like some yogurts, some kefir, and you can usually see that on the food label when you get it. But if it's something you're making yourself, it does not technically meet the definition of a probiotic. But that doesn't mean that there isn't a benefit to it. And so a lot of that also comes down to just historically how we study probiotics. And there could be potential probiotics in fermented foods. We just haven't characterized them yet.

Kate Scarlata, MPH, RD:

Yeah, I think that's really perfect explanation and I think what people miss sometimes is that probiotics need to be alive. So there are some fermented foods that we're baking or pasteurizing and heating in so that kills off the microbe and we can talk a little bit more about that. But just as a reminder, probiotic is live. That's part of the definition. So that's one way to kind of think about it. When you're thinking about fermented foods, If it's been pasteurized or baked, unless you're adding something after the fact, there's definitely not a probiotic in there. But to your point, which is a very important point, that doesn't mean it's not a healthy food or maybe really beneficial to your gut microbiome. It's just that it's not going to fit that little definition right.

Dr. Megan Riehl:

Exactly, yeah, okay. So as a consumer here, sometimes I've had a roller coaster of an emotional relationship with my McDonald's Coke and right now we've divorced and I'm not drinking soda. But now we go into the grocery stores and we're seeing prebiotic soda or the healthier you know. Just again, as consumers and I'm one of them that are going in what are your thoughts on those types of beverages? What's the thinking behind that?

Elisa Caffrey:

Great question. So these terms become very confusing. We have prebiotics, we have probiotics, we now have postbiotics. So, to kind of break those down, we can really think of prebiotics as ingredients that are there to feed the microbes. So usually it's some sort of fiber that's been added where you can have some benefit. The probiotics are these very well-characterized microbes that have to be alive. Probiotics are these very well-characterized microbes that have to be alive. And then postbiotics is this new term where basically, if you have heat killed a probiotic or any microbe that is known to have some sort of benefit, so post-pasteurization you would have technically, these postbiotics. Sometimes people might just add things like lactic acid, which is a metabolite produced by microbes, to a food and call that it has this postbiotic. It gets tricky because in terms of marketing it makes a lot of sense to say we want to try to reconstruct a food that is going to be very stable. So if I have a probiotic soda addition, know, addition of these strains that have this probiotic benefit.

Elisa Caffrey:

But a lot of the work that has been done in fermented foods is looking at these whole foods that are consumed and so you're missing out on a lot of this. You know, fermented foods end up being very messy of, like you know. We generally know what microbes are in there. We can look at that, we can know some of the metabolites and the chemicals they're producing, but there's a lot we still don't know about them, and so when you start breaking apart these foods and trying to put them back in combinations, you might be missing a lot of this benefit.

Elisa Caffrey:

And we still haven't really understood. Do we actually get the same benefit from deconstructing these fermented foods and putting them back together in stable combinations, or is there just more of a benefit to leaving some of this diversity that we would be consuming? Even in a yogurt that has its dairy and these well-defined strains, you still have not fully characterized what the chemical milieu, the number of different metabolites in there, are going to be, and so when you're consuming yogurt day to day, even if you're just consuming yogurt, there are going to be differences in what metabolites you're exactly consuming and the levels, and it's still an open question as to maybe that is. What is really important is getting these different amounts of nutrients and chemical metabolites compared to something that might be very stable and taste very good and be shelf ready. You know, shelf stable but might be missing some of that important diversity and nutritional value.

Kate Scarlata, MPH, RD:

I think of fiber, the same, you know. People always ask, like you know, what fiber supplement do you recommend? And I'm like food first, because there's so much else there. Right To your point, you've got bacteria in this milky substance and it's a live experiment going on and we have no idea what's being made and we know some of it. Obviously there's some acidity, right, there's some flavor profiles that we can detect, but there's so much else going on. It's a little science experiment in a way.

Elisa Caffrey:

Yeah, I mean I think we see this a lot. Even I mean I think of again, wine is not the best example when we really talk about fermented foods for a health benefit, because there still is ethanol in there. But I mean, when you you know you have wine, you might open the same bottle and you might have very different flavors. And that's wine that was made in the same place, it's going to be aged for the same amount of time, but just some little variability in the microbes might lead to these very different changes in flavor and flavor. At the end of the day is a metabolite, and so when we think of that when it comes to health, you can also really understand how, yes, opening two different yogurts might lead to very different metabolites that we're consuming. Both might be beneficial and we just don't know. And so maintaining that nutritional diversity is going to be very important.

Dr. Megan Riehl:

Yeah, keep trying different things you know. And also letting your taste buds explore the different things too, because these all come with lots of different tastes that you know. Depending on your cultural background, your environment, you might try something and go whoa like my tongue is zippy right now and, I think, also letting your kids try different from as young of an age as possible, to get them used to some of this yummy, gut health friendly fermentated benefit food and that's very scientific. That's my scientific explanation of that Non-dietitian here. Tell us a little bit about the various fermentation methods you've started to tell us, but if you can kind of summarize for that, describe them for us and also give us some ideas of which foods use these methods.

Elisa Caffrey:

Yeah, there are different ways in which we can start the fermentation process, but then there are also different groups of microbes that are largely used to ferment. So I'll see if I can kind of break this down in different ways. So, for example, if we're looking at what we call kind of wild fermentation, and so that is really just using microbes that are in the environment, they could be from your hands, they could be from your kitchen. Honestly, there's been a lot of work done in this space and it's still kind of an open mystery of where are the microbes in your sauerkraut really coming from? Where we have a general sense of maybe some of the cabbage, some on your hands, but actually tracking where they come from has been very interesting. And so in that case what you're doing is you are cutting the cabbage, you're exposing some of these carbohydrates for the microbes to start consuming, and so there you end up getting a lot of lactic acid bacteria, and so these are microbes that largely produce lactic acid, and so you get a very specific flavor, and we see this again. If you're doing any sort of brine ferment so let's say you're making carrots and then add 2% salt and water, that is also lactic acid ferment you could be doing kimchi as another example where the microbes come from the environment, end up in your jar fermenting and you have this lactic acid fermentation happening.

Elisa Caffrey:

Lactic acid fermentation is also in dairy. In this case we're not adding the salt and we might be adding specific strains, but we see this in cheese, in yogurt, in kefir, and so we have kind of a number of other ferments in the dairy space where we tend to pasteurize the dairy first and then add in our specific strain of interest. Then we also have acetic acid fermentation and that's largely vinegar and kombucha, and so in that case we have a SCOBY, which is this symbiotic community of yeast and bacteria, and in that case we have exactly both a mix of the yeast and the bacteria that are used as a starter, and the actual thickness of the SCOBY itself is a lot of cellulose, and so you're able to kind of passage that where we don't know the exact strains that are present. But we have this fairly stable community and it's fun to kind of two different people making kombucha and you compare it. The flavors are totally different when you make them at home, but the general idea should be it's very similar bacteria and similar yeast. So that's always fun to kind of explore that.

Elisa Caffrey:

And then we also have yeast fermentation, where we can think of largely, let's say, in sourdough as well, where when you're making your own sourdough you're going to have both lactic acid bacteria and yeast. That's present. But you could be purchasing a yeast strain and adding it in and that might not be as diverse in terms of the microbial community, but you're still getting the yeast that is fermenting. And that's very different from breads that are made with chemical leaveners, so in that case it would not be a fermented product and of course you also have. Again, I keep going back to winemaking, but wine is made with yeast as well.

Dr. Megan Riehl:

You are in California.

Elisa Caffrey:

I know.

Dr. Megan Riehl:

Napa is right down the road.

Elisa Caffrey:

Exactly.

Elisa Caffrey:

And then we finally also have filamentous fungi, and so that's when we think of aspergillus oryzae, which helps to make miso, or rhizopis oryzae, which is to make tempeh, for example, and so in that case we usually have some sort of legume the soybeans that are steamed, and that helps to kind of sterilize the environment, and then we're going to add in a starter of the different fungi that we're interested in the different molds, and in that case we're really trying to avoid a lot of bacterial growth and just get this filamentous fungus to kind of take over the environment. And the advantage of the filamentous fungi is that they're really, really good at making enzymes to break down certain products, and so they actually help to break down the soybean and or, you know, in certain cases rice, and really make either this kind of beautiful savory umami flavor or the sweet flavor for things like amazake, which is a mix of rice and aspergillus . So there are so many methods and there really is if you don't like sauerkraut.

Dr. Megan Riehl:

There's so many other options out there to try. What would be your recommendation of like if this is brand new to you? Where might you encourage people to start? And, kate, I'm sure you have lots of opinions on this too. But what do you think if the family isn't really thinking much about fermented foods?

Dr. Megan Riehl:

Where do they go?

Dr. Megan Riehl:

First?

Elisa Caffrey:

I feel like yogurt is always a good place to start in terms of kind of flavor palette, but I also think just starting slow and just small little bites of sauerkraut, small little bites of kimchi, I think often, especially when you have the strong lactic acid flavor, can be very overwhelming.

Elisa Caffrey:

But just, I don't know, trying different things. The other kind of interesting thing that has been reported in some of the participants of the dietary interventions that the Sonnenberg Lab has done in collaboration with Christopher Gardner's nutrition group has been that they often report that they might not really like fermented foods to begin with and then, once they start eating them, they start craving them. And we see that in some of the work where, even after participants were told you know you don't have to eat fermented foods anymore, you know you can go back to your normal diet, they still continue to eat them and that they just become incorporated in their diet, and so the science behind that needs to be explored. But I think that's very exciting. And so just saying you know, try different things, put them together, see what you prefer, might open up doors to novel flavors that might have some sort of benefit as well.

Kate Scarlata, MPH, RD:

We add sauerkraut to sandwiches and just do small amounts, and different sauerkraut has different flavor profiles. So like trying that and just kind of almost like lettuce on a sandwich. You know just a little bit of it. It's a little tangy, little salty. You know that's somewhere I might start and my kids actually like sauerkraut. So I think, like everything, the more exposure you have to these things and with yogurt you know you can get Fage yogurt which is very kind of creamy and not very acidic, and then other brands that might be have more of that lactic acid really tang. So I think even across yogurts you can get different flavor profiles as well.

Kate Scarlata, MPH, RD:

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Kate Scarlata, MPH, RD:

Back to sort of the fermented food studies, and I know the one that I believe the one you were quoting on was the fermented foods versus high fiber diet. So it was a 40 gram fiber diet versus six servings of fermented foods and in that study they used all live containing fermented foods, so the microbes were alive. They weren't using sourdough, for instance, in that particular study. So is there advantages of selecting fermented foods that have live cultures versus? I mean, I know, let me just plug my little low FODMAP. I do a lot with IBS patients and you know sourdough bread, when it's slow fermented, is actually tends to be lower. It can be a little higher in mannitol sometimes but for the most part lower in those fructans which are the biggest culprit for most people, and so that really affords them to have that. So I love sourdough. That's an advantage and there's no live bacteria. But overall, if you had to be zoomed out. Do we want the live microbes first and foremost, or are they just all great?

Elisa Caffrey:

in different ways. That's a great question and has really changed, I think, in the past few years, even in terms of the way we think about it. When the FeFiFo paper or the study, this fiber fermented study, dietary intervention was first designed. Fermented study, dietary intervention was first designed. A we're kind of we I was actually not part of that study at all the group really went in with just kind of the current understanding of general consensuses eating live microbes is good, we want raw, wild, fermented foods. It was designed just trying to test our fermented foods, even interesting to look at. Right, it was meant to really be a control group for the fiber arm of the study, and so that's why you know there was a selection towards maintaining kind of live microbes.

Elisa Caffrey:

But there have been a number of studies since then that have come out that compare pasteurized versus and this has largely been in sauerkraut specifically pasteurized versus unpasteurized and in certain cases. So there've been three studies that kind of come to mind. The first was in 2018, which is this Nielsen et al that was comparing patients with IBS, saying pasteurized versus non-pasteurized, and they found that both had reported kind of relief from symptoms, and so they were like, okay, there's no real difference between pasteurized and not pasteurized for this population, and so that was kind of a first indicator of maybe for people who might be more sensitive to some of these foods when they're not pasteurized, having pasteurized foods might be good. Another study that is currently in bioarchive which is from someone in the lab, sean Spencer, was looking at differences in immune cell type, called regulatory T cells, which are very important for maintaining immune homeostasis in the gut, and he was comparing sauerkraut brine to filter sterilized sauerkraut brine, so no microbes, or the kind of brine with the metabolites in it, and he found that there was a similar increase in these regulatory T cells, so the cell type really important for preventing inflammation.

Elisa Caffrey:

And then this other study that has come out this year, which has been very exciting, that was again doing this fresh sauerkraut or this unpasteurized versus pasteurized, and they actually did it. You know this very elegant study which is this crossover study and so where you have participants eating sauerkraut that is pasteurized and then have a four-week washout period so they stop eating sauerkraut and then switch to either the pasteurized or the not pasteurized and you have two groups at the same time that are swapping. So it's a really good way of seeing what the actual impact is of this certain food on the diet, because you have time when you're consuming it, then you're not consuming it anymore, so you can see what's going on and then you go back to it, and what they found was that participants that were eating the pasteurized sauerkraut actually had an increase in plasma short-chain fatty acids.

Elisa Caffrey:

And short-chain fatty acids are a type of metabolite that's primarily made by microbes in our gut microbiome that are known to have, for the most part, a very important benefit for our immune system, and so these are kind of just early indicators that it might be the chemicals themselves that the microbes are producing that might have more of an impact, if not the same impact, and so we've been really interested in exploring this, particularly with patients where it might not be recommended for them to consume fermented foods if they're live or raw, for example, with immunocompromised patients, where the idea is we have this benefit to the actual fermentation process itself that the chemicals microbes are making are likely having a positive impact on the immune system, and so if we pasteurize them and so you're not consuming the live microbe, you could be getting the same benefit.

Elisa Caffrey:

And so they're designing some clinical interventions now that are trying to explore this more, but I would say, as of right now, if you are a patient who might be a little sensitive to consuming fermented foods, consuming the pasteurized version of that cooking with it is a great way of incorporating those foods into your diet. And again, there also are so many different fermented foods that really finding foods that you might not be as sensitive to is going to be very important. But for the most part, yeah, our understanding is diversity is important, so find what works for you and if you need to cook it, pasteurize it. That sounds great, as long as you're incorporating some of that into your diet.

Kate Scarlata, MPH, RD:

Love it. Who knew, who knew? I figured oh, it's got to be the live, it's got to be the live, but it's really what they're doing in there before we even eat it. Exactly.

Dr. Megan Riehl:

So cool. It's very cool and we both do a lot of work in the IBS and DGBI space and I work with a lot of patients with inflammatory bowel disease and both groups of people are at higher risk for anxiety and depression. It's kind of this bi-directional experience and when we think about various multifactorial treatment opportunities, where is the science right now in kind of fermented foods and people's mental health and gut health in general?

Elisa Caffrey:

I think that is a prime area for exploration.

Elisa Caffrey:

There've been a few groups like John Kryan in Ireland has been doing some really amazing work in that space and exploring that as we learn more about the gut brain axis and the way in which not only does diet impact your gut microbiome but fermented foods right, making these metabolites that could have a direct impact on your gut brain axis and gut health, I think is really important to continue to explore.

Elisa Caffrey:

I think we're still kind of in early enough stages that it's hard to make a direct recommendation, but I would say that I've also just talked to people that there's one person specifically I'm thinking of who has ADHD and during COVID, started making sourdough and was just telling me how making sourdough grounded them in time, especially during this kind of COVID time and so part of it too, of like, yes, there's the benefit of the consumption, but I think there's also benefit to the practice of fermentation where again, kind of connecting to your food and you know when you're having to take care of something also has this kind of added benefit which I think is very exciting to really think of when it comes to mental health and, yeah, and kind of wellness as a whole, that this kind of reconnection to preparing food and engaging has this kind of large benefit and just feeling like you know you're making something, that you're, you're raising these microbes and you're consuming it, and so there's also that benefit to it as well, it just reminds me of like people that were like naming their starter and like it became such a hobby, and I love that idea, that concept of you know you are more thoughtful about what you're putting in, you're stopping, you're thinking through the process, there's some science, but you're getting those little zaps of endorphins that are great for our mental health and our well-being.

Dr. Megan Riehl:

So maybe not a prescribed treatment for anxiety or depression yet, but very cool area of research coming down the pipeline.

Kate Scarlata, MPH, RD:

Yeah, definitely yeah, I'm like cooking is my relaxation. My husband's always like you've got a lot going on. Why are you in the kitchen? And I find it from a mental health standpoint it is very relaxing. So maybe yeah, there's something there, but I do think it's just like growing your own food in a garden. Right, there's this whole, you know, like raising a child not quite, but that it's something you've nurtured and that makes us feel good. When we think about fermented foods, are there any potential risks? I know like kombucha can have alcohol, for instance, and miso is high salt. Are there any negatives? Or patient populations Obviously immunocompromised. We want to be careful with live active cultures, maybe.

Elisa Caffrey:

Yeah, there are a few kind of key examples. The first, I would say, are histamines, so people who are histamine intolerant, fermented foods I don't know if there's been a kind of a survey across all fermented foods to see which ones might be higher or lower in histamine, but for the most part it's understood that there is histamine production in fermented foods. You know, I was actually just some of the work that I was recently doing was comparing sauerkraut made with green cabbage versus red, and there are differences where the ones made with red cabbage tends to have lower amounts of histamine. But that really has more to do with how tolerant an individual is more than kind of the food itself, cause there's some people that can eat unlimited amounts and they're mostly fine. Individuals who are also on MAOIs so monamine oxidase inhibitors that's usually treatment for depression might be sensitive to high levels of tyramine, which might also be in certain fermented foods, like certain cheeses that are aged for a long time, and so just being more kind of mindful of that Sodium is kind of a big. It's honestly a very interesting one because, yes, fermented foods primarily, not just vegetable ferments where you have two percent salt usually, but also misos that could have up to 20 salt.

Elisa Caffrey:

There's certain studies that have looked at for, I think, primarily in mouse and rat models of high blood pressure. They give them miso and they actually don't see an increase in blood pressure in these cases, and soo, and they actually don't see an increase in blood pressure in these cases. And so the question is what is going on? Are there other compounds in there that might be having an impact? And the way that we're defining servings right now is just based on one tablespoon of miso is considered a serving, but maybe for individuals that have high blood pressure and need to watch their sodium intake, a smaller amount might have the same benefit, but you don't have as much sodium. But that is kind of an open area, and so I think it's I'm a little hesitant to kind of make any recommendations, but there's kind of interesting work happening there.

Elisa Caffrey:

But again, there are fermented foods that are lower in sodium, like dairy ferments and some of the filamentous fungi tempeh right will have.

Elisa Caffrey:

You don't use as much salt in those to actually produce them, and so there are kind of opportunities there to still incorporate fermented foods without having to consume foods that might be higher in in sodium.

Elisa Caffrey:

And then of course there's, yeah, immunocompromised individuals, people who are pregnant, where technically they're still in this kind of gray space where consumption of live microbes, especially in higher abundances, might not be recommended, but again going to kind of pasteurized fermented foods and using those instead With the pregnancy, it's very exciting. There is the follow-up from this FeFiFo study. There's a study now that's ongoing called the MOMS study, which is a maternal offspring microbiota study that is being written up and should be published very soon and that was comparing pregnant women who either were consuming high fiber, high fermented food both at the same time or their kind of normal diet, and so hopefully in the next year they're going to be kind of new recommendations or new indications for what are the best recommendations for pregnant women when it comes to fermented foods, and so that I'm very excited about that. That study it's. I'm not a part of it, but I've just seen some of the results and it's very cool.

Kate Scarlata, MPH, RD:

Very cool. Cause I remember early you know, following gut microbiome science and just the different changes that women's microbiome goes throughout the trimesters and there was some signals that, like in the third trimester, there were some changes that almost looked like diabetic microbiome, so probably some microbiome way to add weight to your body or whatever it is that it's doing. That's probably protective, but it looked very similar to individuals with diabetes.

Elisa Caffrey:

So it'd be interesting to see how we manipulate our diet and what that does, and from a number of different factors yeah, what I think is really exciting about the study as well is that not only are they following the women up to birth, but they're actually going to follow the influence up to five years of age.

Elisa Caffrey:

And so this is also getting at the idea of you know, if you're able to change your gut microbiome while you're pregnant, does that affect what microbes are passed on to your infant? And if we know this, you know relationship between the gut microbiome diversity and the immune system, could you potentially have a lower risk of having your child develop some of these food intolerances, for example like peanut allergy? And what role does having a diverse microbiome during pregnancy or consuming certain diets during pregnancy have on the offspring and kind of your infant health? So the first part of the paper of just looking at the women and the birth outcomes is going to come out, I think, in the next few years and then in five years time, once they've followed up on all these children. Then, yeah, we'll have kind of this longer term follow-up, but it's very exciting.

Dr. Megan Riehl:

You've talked a little bit about the power of these little active microbes and, rather than just and going beyond, just identifying them in the gut, and so can you explain the importance of the microbial metabolites like lipopolysaccharide or LPS, from gram-negative microbes and how this is beginning to shift our understanding of gut health?

Elisa Caffrey:

So LPS, which is it's part of the outer membrane of gram-negative microbes, and most fermented foods are not gram-negative, so we really should not be getting that much in the fermented foods at all, and in fact, there's been some kind of early evidence that some fermented foods which are largely gram-positive, might actually impact and decrease the abundance of LPS in your gut. Your gut also should not be high in LPS. Usually, it's a sign that something weird is going on, and so that tends to be, yeah, not of a lot of concern when it comes to fermented foods. But certain things like short-chain fatty acids, which we know, for example, acetate and lactate, are short-chain fatty acids. They're made in your body. They're made in your gut microbiome by your gut microbes, but they're also made by your microbes in sauerkraut and kombucha, and so there are these really interesting parallels where we have right in our gut microbiome. We're consuming a food, the microbes make these short-chain fatty acids and these other metabolites Aerolactates, for example, are another kind of class of compounds that have been of interest but when you're consuming a fermented food, the same thing is happening.

Elisa Caffrey:

You're taking your fiber, you're taking your dairy, they're making these compounds and you consume them and they're going to be absorbed. We actually still need to figure out exactly which compounds are rapidly absorbed and which ones are degraded, because, honestly, the gut is a black box and so it's hard to figure out exactly what goes on in there. But understanding what is it in fermented foods that might actually be absorbed and have different impacts on health. And so we know again that in your fermented food you're going to get some of these short-chain fatty acids, you're going to get some of these arylactates and just kind of a number of compounds that you might be able in the future to personalize, to say, even for just comparing green and red sauerkraut, their differences and what metabolites are actually being produced. But maybe we can make a microbial community that's going to be really good at making one specific compound that maybe you are deficient in and try to see if we can kind of use that to target the yeah, kind of target your health and make personalized fermented foods.

Elisa Caffrey:

And so it's been very exciting and interesting to really explore this metabolite and chemical space, because I had gone in assuming, you know, it's a vegetable ferment, they make lactic acid, they must make a lot of similar stuff, and it turns out that they don't, that there are these kind of you know, large, really abundant metabolites, primary metabolites, like the short chain fatty acids that they do make, that are similar, but the amount, even of lactic acid, is going to depend on how long did you ferment, what type of substrate. Different kimchis are going to have different amounts, different dairy products are going to have different amounts, and so, getting at, you know, can we standardize these? Do we want to standardize them? What is really happening is, yeah, it's very exciting, but the kind of general takeaway is that they're diverse. Diversity does matter, and we just know that difference in fermented foods and consuming different fermented foods tends to have that beneficial effect, and so just keep trying different things.

Kate Scarlata, MPH, RD:

I like that. You know I think about. So a couple of things I want to ask. So you know, when we talk about eating fiber, we're feeding the microbes that already exist in the gut. I mean, it's a prebiotic. That's the role there. When we're eating fermented foods, that's the role there. When we're eating fermented foods, we're adding a bunch of stuff the metabolites, microbes that maybe never existed in our gut.

Kate Scarlata, MPH, RD:

So just so many potential things, things going on there, which is really really so exciting, and I'm definitely going to be upping my fermented food intake. I'm jazzed about this whole topic and I feel like I'm pretty good about it, but I think variety is lacking. I need to get a little bit more exploratory with some of these things. But for our listeners and again, you've made it very clear that fermented foods have so many potential health benefits just on their own, whether they're a source of probiotic or not. But for those that are interested in selecting a fermented food that is a source of a probiotic, what do they look for? What does a consumer look for at their local grocery store to say, oh, this is sauerkraut with a probiotic or this is yogurt with a probiotic? Are there tips and tricks for them when they go to the grocery store.

Elisa Caffrey:

Yeah, so I mean in some ways, because these probiotics have to be well-characterized.

Elisa Caffrey:

The advantage is they also have to be listed on the ingredients because you're adding them to the food and so you should be able to just look at the ingredient list and either have them listed under the ingredients or sometimes they might say contains live active cultures and then has a list of the different probiotic strains.

Elisa Caffrey:

Sometimes it gets very tricky to know whether it's just a kind of added mixture of defined community and they have the list, or whether it's actually a really clearly defined probiotic. And so usually a probiotic will have not just the name of the species but also some sort of number or some sort of letter after it, and so that could also help you. If you were interested in kind of tracing where that came from, what the genome was, what the benefits are, you can actually go and kind of find that it does get very messy in the, especially in the kind of the food space, so it does get very hard to identify some of these. I mean yogurt I think is the best example of a food where usually you look at the back and it will say you know, streptococcus thermophilus, and then some sort of number or some sort of bulgaricus strain, and then a number behind it. I mean, yeah, it does get very tricky.

Kate Scarlata, MPH, RD:

It's a little tricky. I like when they at least use the term probiotic. Maybe that helps a little bit probiotic yogurt?

Elisa Caffrey:

No, exactly, although that gets tricky as well because there's no regulation, at least in the US, as to how to use these terms. And so you could go and I've seen it kind of at farmer's markets where you know a jar of sauerkraut will say a probiotic sauerkraut and it technically does not meet the legal definition.

Kate Scarlata, MPH, RD:

But you know, you also want to sell your product and say it has live microbes and so yeah, yeah, maybe if there's a certain product that you really like and you're curious, I guess you could go on their website and learn more specifically about a specific yogurt or a specific sauerkraut.

Elisa Caffrey:

Yeah, but it is a little murky, it is murky, and I would say for the most part, if someone is actually going out of their way to purchase a probiotic and put it in the food, they will let you know. So yeah, going to their website, you should be able to figure it out and they'll have the information there.

Dr. Megan Riehl:

Perfect. Yeah, I'm in Michigan and there's just been a lot of sickness over the winter, a lot of antibiotics flying around and I'm just thinking that like an easy way to help diversify your gut microbiome after you know you've given your kid another antibiotic for their ear infection. You know, yogurt is a good one. I know that it feels easier for us to grab something, and so am I right on that. Is that a good way to go?

Elisa Caffrey:

Great question. I don't think anyone has done that specific study saying are fermented foods a good way of restoring the gut after antibiotic use?

Dr. Megan Riehl:

But yeah, I don't know if I want to speculate too much on it, but it sounds yeah, that's okay, I'm going to keep doing it. I don't know, but you don't have to.

Elisa Caffrey:

What has been really interesting about the increase in diversity that we see following fermented food consumption is that when researchers are actually trying to identify, you know, the first question would be are these actually coming from fermented foods? So you see this increase in diversity and most of them are not. And so it's also like is this actually? It's not like, you know, you eat a yogurt and then suddenly, or the streptococcus thermophilus from the yogurt suddenly will integrate into your gut. That's likely not happening. There must be something about the fermented foods itself.

Elisa Caffrey:

Maybe again this kind of the mix of metabolites that you're consuming, I don't know, the like interaction with microbes in the food that is either leading to an increase in microbes that are already in your gut but just below levels of detection that might be kind of coming up that allows them to grow better, or it primes your gut microbiome to be a place where, I mean, you're exposed to microbes all the time, right?

Elisa Caffrey:

So when you swallow, you're going to get some microbes in there. When you touch a surface and you you know, just on the surface of your food you're going to have something, and so does it just change your gut environment to allow it to be a place where microbes are just more easily integrated from the environment into your gut. We don't know. And so I think the idea of if you take antibiotics and then you take yogurt, are those strains going to be replacing your gut microbiome? I don't think so. I think there likely is still some sort of general change happening to the gut environment itself as a whole, and that's kind of again like an open question. But I think it's also very, very exciting in terms of, yeah, where are these microbes coming from and how are we getting a more diverse gut? But somehow fermented foods are doing that and helping.

Dr. Megan Riehl:

And you've mentioned, you know in terms of like how much we can consume or should consume. It could be as little as you know, a few bites to introduce it, but is there any science around like how much we should actually try to intake, right?

Elisa Caffrey:

Now I would say it gets tricky because we still don't really know how to define a fermented food serving. So again, with miso, we say one tablespoon, because that's what was on the container, but maybe, you know, we should really be thinking about this in terms of a total number of live microbes a day, or a total abundance of a certain of like lactic acid or acetic acid you should be consuming in a day, and so we haven't quite been able to identify that yet as a kind of where do we see this benefit? I think that's something that this mom study is trying to look at a little bit, because I think a fourth of a cup is one serving of sauerkraut. But then you might go and you get these. You know, a bottle of kombucha, that's two servings, and so if you drink one you get two, and there were some participants in these studies that were having insane like based on the like being like 30 servings of fermented foods in a day, which is a crazy amount and like all of us are kind of like.

Elisa Caffrey:

What does that mean? Like, how is that possible? And a lot of it is just based on one tablespoon of some concentrated coconut ferment might count as a serving and so you might have multiple and so it's hard to know still kind of what is a serving size. But just trying to incorporate whatever works for you. And I mean I just like to think of it more in terms of how many times a day did I eat a fermented food?

Elisa Caffrey:

And if I had a shot of sauerkraut brine and then some of that sauerkraut, I count that as two like like you know, two different things, mixing maybe some kefir and some yogurt. I think less about volume and more about just how do I optimize the different types of either microbes or metabolites that I've consumed in a day that come from different microbes, and so that's kind of been my approach to it. But I think we're still a little too early in terms of kind of upper level, especially when it comes to even, you know, patients with IPS or on a low FODMAP diet that might want to restrict the number of live microbes they're consuming or might be more sensitive to them. You know, I think the idea of just consuming as much unpasteurized sauerkraut or you know whatever might not be a great idea because you might have these, you know, gi effects and so you know if you can get to a certain level you can get to two, three servings and you still feel good, then that's great, great.

Kate Scarlata, MPH, RD:

So lots to unpack. I'm thinking, okay, sauerkraut brine shots, let's go, let's go yeah, yeah, exactly.

Kate Scarlata, MPH, RD:

The other thing is well, I know, in the study with the high fiber and the fermented foods, there were six servings and they did break it down. It was like that quarter of a cup of kimchi, for instance. It sounds like six servings, sounds like a lot, but when you looked at the serving sizes it didn't overwhelm me, you know. But yeah, I think listen to your body is what I try to say to my patients that I'm working with, with IBS, and if they're upping, you know, a lot of sauerkraut or kimchi and they feel distressed, then to dial it back a little bit, right? So we always, you know, like to wrap up our episodes. Today this has been fantastic with you know. Just a personal take on our guests you know what they do for themselves, for their gut health and wellbeing, and we'd love you to share something with our audience.

Elisa Caffrey:

I mean I kind of got at this earlier, but I really like to think of it as just how diverse is my fermented food and fiber intake for the day.

Elisa Caffrey:

So I mean it honestly turns more into a game where I just kind of you, look at your plate and you say how many of these things have some sort of microbial connection to them? You know, soy sauce, miso, you know, maybe I add some sauerkraut brine into a dressing that I'm making and just try to kind of add all those up, you know, and of course, fiber, of like how many different types of fiber? And when you really start thinking about it you can get not only very creative but also just makes it fun. We're like you know what? I'm just going to throw these extra seeds on there Cause I want to get up to five things on my plate today that are these things versus just four. And it just also just makes me become much more mindful of what I'm eating and really kind of think through you know, where do these foods come from? How are they processed? It makes it really fun.

Kate Scarlata, MPH, RD:

It does make it fun. I'm a big nut and seed queen and I'm adding them to everything. But I'm definitely going to get into the sauerkraut brine movement and add it to my salad dressings. But you know, variety is important, right? There's so many, like we're thinking about the different types of microbes in different fermented foods. There's so many different polyphenols and different types of fiber that is fermented in different areas of the colon, and so, again, variety is the queen here, absolutely.

Dr. Megan Riehl:

Well, huge. Thank you, Elisa, for coming on our show today and to all of our listeners, we hope that you will subscribe, follow and like The Gut Health Podcast. Your support means the world. Friends, thank you for joining us as we grow this gut health community. We hope you enjoyed this episode and don't forget to subscribe, rate and leave us a comment. You can also follow us on social media at The Gut Health Podcast, where we'd love for you to share your thoughts, questions and experiences. Thanks for tuning in, friends.

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