Are Vegetarian Diets Better for the Microbiome?

What we can learn from these studies is only that the average person who eats red meat has a disrupted gut microbiome compared to the average vegetarian. That’s the only thing a study like that can tell us. It doesn’t tell us whether it’s because of the meat or because it’s the buns that they’re eating, like, the hotdog buns and hamburger buns around the meat, or it’s the sugar, or it’s the other crap that they’re eating, or it’s a lack of exercise, or it’s that they smoke more frequently.

In this episode, we cover:

2:27  What Chris ate today
6:05  How meat consumption affects the microbiome
11:30  The biggest diet factor that determines gut health
25:28  The importance of the context in which you eat meat

Links We Discuss

• Comparison with ancestral diets suggests dense acellular carbohydrates promote an inflammatory microbiota, and may be the primary dietary cause of leptin resistance and obesity

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Steve Wright: Good morning, good afternoon, and good evening. You are listening to the Revolution Health Radio Show. I’m your host, Steve Wright, co-author at SCDlifestyle.com. This episode of RHR is brought to you by 14Four.me. This is a 14-day healthy lifestyle reset program. Chris Kresser has put together a program here. If you’re someone who’s still struggling with, maybe, digestive issues, skin problems, low energy, maybe insulin issues, basically all these conditions, all health conditions are foundationally supported by diet, sleep, movement, and stress. Now, incorporating all four of these variables into your life can be very hard, especially if you’re having to make tweaks in all of these areas at the same time. Chris knows this, he’s been studying psychology and habit formation for a long time, and so what he’s done is he’s put together this 14-day healthy lifestyle reset program, where you’re going to actually work on your diet, your sleep, your movement, and your stress all at the same time, and by the end of the program, you’ll have incorporated the foundational pieces you need to get over these issues. Check it out at 14Four.me.

All right, let’s get on with the show here. With me is integrative medical practitioner, healthy skeptic, and New York Times bestselling author, Chris Kresser. Chris, how are you doing today?

Chris Kresser: I’m great. How are you, Steve? Good to talk to you. It’s been a while.

Steve Wright: Yeah, yeah, it has been a while. I’m recovering from a sinus infection.

Chris Kresser: Oh, man. I’m sorry to hear that.

Steve Wright: Eh, it’s OK. It happens when you don’t do those four foundational steps.

Chris Kresser: Right. You need a little 14Four spring cleaning, huh?

Steve Wright: Yeah. You try to have too much fun and do too much work at the same time.

Chris Kresser: Mm-hmm. Yeah, that’s not sustainable for very long. It might work for a short time but definitely not over the long term, as you’re finding out, right?

Steve Wright: Yep, yep. I have to make the mistake, like, every three months or so.

Chris Kresser: Right, just to remind yourself.

Steve Wright: Yeah, the body’s just trying to train me.

Chris Kresser: Yeah, got it. Well, I hope you get well soon.

Steve Wright: Yeah, I’m on the mend. It’s all good. So what have you eaten all day today?

What Chris Ate Today

Chris Kresser: I had scrambled eggs; sweet potato hashbrowns; and raw sauerkraut with cabbage, beets, and carrots for breakfast. And I had kind of an unusual lunch because I had a lot going on and I knew we were sitting down to record, so I just had some yuca crackers from Mission: Heirloom. A really awesome thing that they do. Sylvie loves them, and we send them with her to school for her snack at preschool. They’re made from yuca, AKA manioc or cassava. It’s grated and then pressed and dried into crackers, and I put some ghee and sea salt on them, sometimes some avocado. And I had some olives, Castelvetrano olives, green olives, which are my favorite. I had some salami, some raspberries. It’s similar to, like, food that I take with me on an airplane. A little bit of sliced chicken and some kale that we had leftover, so it was kind of almost like tapas, although there was nothing Spanish about the food but just in the sense that it was like a smorgasbord, I suppose.

Steve Wright: Yeah, more like a summer picnic.

Chris Kresser: Yeah, exactly. Got it.

Steve Wright: Have you tried the Boulder brand avocado oil sea salt chips?

Chris Kresser: No, I haven’t. Are they potato chips, you mean?

Steve Wright: Yeah, so it’s just white potato.

Chris Kresser: Oh, yeah, yeah, yeah. Yeah. Avocado oil. Yeah, those are pretty good.

Steve Wright: They’re dangerous.

Chris Kresser: Yeah, exactly. I mean, certainly they’re better than eating chips with industrial seed oils, and they’re a great snack, but if you eat, like, two bags, it’s probably not doing you any favors!

Steve Wright: Probably need 14Four.

Chris Kresser: Yeah. But we have a really great question. It’s from Dr. Akil Palanisamy, I think, is how you pronounce it. I hope that’s correct, and I apologize if it’s not. I’ve met Dr. Akil before, and he’s a functional medicine practitioner in San Francisco, and he has a really good question that a lot of folks have asked and a lot of people will be interested in, so let’s give it a listen.

Question from Dr. Akil Palanisamy: Hi, Chris. This is Akil Palanisamy, integrative medicine physician in San Francisco. I have a quick question for you about meat consumption and the microbiome. When I was reviewing the literature recently, I came across some studies that surprised me, suggesting that eating meat could have an adverse impact on gut bacteria and that a vegetarian diet may have beneficial effects on the gut microbiome and markers of gut bacteria. I’m wondering if this is related to antibiotics in commercial meats that are having a negative effect on gut bacteria. I couldn’t find any studies that looked at pasture-raised meat or antibiotic-free meat, and I wonder if that would have a better impact on gut bacteria. It’s a very important question, I think, because many patients that I see have a problem with their microbiome, and I’m trying to restore it, and if eating meat has an adverse impact on it, then that would really change my dietary recommendations for people. Thanks for your response.

How Meat Consumption Affects the Microbiome

Chris Kresser: OK, so I’m sure some of you have seen articles in the mainstream media about this or have seen some chatter in social media or whatnot, and it is true that some studies show that vegetarian diets are better for the microbiome and eating meat is associated with unfavorable changes in the microbiome. But once again, you have to understand the issues with most of this kind of research. To get a much more detailed discussion of this, go back a few podcasts and listen to the research 101 show that we did where we covered all of these issues much more extensively, but most of these studies are just comparing two groups of people. They’re comparing meat eaters and vegetarians, and then they look at the microbiome in each group and then they come to some conclusion where they say, OK, people who eat meat generally have a worse microbiome than vegetarians. The problem with drawing that conclusion is that we know from other studies that the average meat eater does a lot of things differently than the average vegetarian. They eat fewer vegetables and fresh fruits. They don’t exercise as much. They tend to smoke more. They consume more alcohol. They engage in all kinds of other behaviors that can adversely affect the microbiome, and studies do try to control for some of those other confounding factors, but they can never control for all of them.

What we can learn from these studies is only that the average person who eats red meat has a disrupted gut microbiome compared to the average vegetarian. That’s the only thing a study like that can tell us. It doesn’t tell us whether it’s because of the meat or because it’s the buns that they’re eating, like, the hotdog buns and hamburger buns around the meat, or it’s the sugar, or it’s the other crap that they’re eating, or it’s a lack of exercise, or it’s that they smoke more frequently. Those other factors are, more than likely, what are causing this difference. If you extend that, of course, it doesn’t mean that a person who eats red meat that is also eating a lot of fresh fruits and vegetables and fermented fibers, fermented foods, that isn’t eating a lot of refined sugar and industrial seed oils, that is exercising and sleeping and taking care of themselves is going to have an inferior microbiome compared to someone that’s doing all those things and not eating meat. There is no study that I’ve seen that has come to that conclusion.

Steve Wright: Yeah. I’ve looked at this stuff quite a bit as well, being something I care about, and I’ve thought about it a lot in my diet, and so I’ve tried times of vegetarianism just to kind of see what it was like and also during, like, my vipassana retreat.

Chris Kresser: Yeah.

Steve Wright: And what I think is also not being talked about in these studies besides everything you’ve already mentioned is that typically because when you go vegetarian, you need more calories and you end up eating a larger quantity of fermentable fibers.

Chris Kresser: Mm-hmm.

Steve Wright: Versus somebody who’s maybe satisfied earlier because they’re consuming animal content. They might end up eating less fruits and vegetables over time just because they need less volume to feel full and satiated during a meal.

Chris Kresser: That’s true. That’s definitely true, and of course, the question there is, does that adversely affect the microbiome? I haven’t seen any studies that suggest that it does. I mean, we’ve looked at traditional cultures that have meat in their diet but also eat relatively high amounts of plant foods, you know, fruits and vegetables and tubers and other plant parts, and they have an ancestral microbiome. So I don’t think we can say that it has much to do with the meat, but it does have to do with the intake of other stuff — we’re going to come back to that — and also non-dietary factors, like sleep and exercise, we know affect the microbiome as well.

When people read these kinds of articles or hear about them on social media or on the news, there’s a natural and understandable tendency to kind of identify with the meat eater and place yourself in that category and assume that you are in that group and are subject to those same conclusions, but it’s not true actually. Most of the people who are listening to this podcast are not representative of the meat eaters in scientific studies. That’s really important to understand. So if you ever hear of a conclusion that’s being drawn of red meat eaters in scientific research, you are not that person typically. Of course, it depends on the exact study and what they’re looking at, but most people who listen to this show are eating meat in the context of a diet that’s rich in all the things that are beneficial for gut health, and so we cannot extrapolate the results of meat eaters in these studies to all of you who are listening to the show.

The Biggest Diet Factor That Determines Gut Health

So if it’s not the meat, what is the biggest factor that determines the health of the gut microbiome? I think it is the type of carbohydrate that you eat, and specifically, it’s the ratio of acellular to cellular carbohydrate. Now, that sounds very geeky, I know, but just give me a chance to explain it a little bit because it’s a very useful concept to understand, and I think it answers a lot of questions, and you’ll see what I mean as we go through this.

This concept of acellular versus cellular carbohydrate and the importance of it to the gut microbiome comes from one of my favorite research papers ever, which was written by Professor Ian Spreadbury, and he’s actually going to be a presenter at the Ancestral Health Symposium conference in New Zealand, the New Zealand version of that conference, which is happening in October of this year. And the paper is called “Comparison with ancestral diets suggests dense acellular carbohydrates promote an inflammatory microbiota, and may be the primary dietary cause of leptin resistance and obesity.” That’s a mouthful. The study will be in the show notes, so you can check it out. The full text is free, and you can read it if you’d like, but the basic idea is that all carbohydrates that were part of the ancestral diet, which would be tubers, fruits and vegetables, plant parts like stems and leaves, store their carbohydrates in fiber-walled, living cells, and those cells remain largely intact during the cooking process, and they also resist digestion or absorption in the small intestine, and therefore, the fiber remains intact all the way down to the colon, where it then becomes food for beneficial gut bacteria that are living in the large intestine. So those are the cellular carbohydrates, and they’re, like I said, found in all ancestral carbohydrate sources.

On the other hand, in the Western or industrialized diet, you have a lot of acellular carbohydrates. These are things like flour, sugar, and other processed starches that have no living cells. These industrial foods are much higher in carbohydrate density than anything the microbiota of our upper GI tract would have encountered during our long evolution. And these foods, because they have no living cells, they’re absorbed higher up in the GI tract, and they can stimulate the overgrowth of bacteria in the upper GI tract, AKA SIBO, or small intestinal bacterial overgrowth, and they preferentially will feed some species of bacteria over others, and that can in turn lead to an inflammatory gut microbiota.

Dr. Spreadbury makes the argument, which I agree with, that this difference in carbohydrate type could be the single most important difference between ancestral and industrialized diets. Now, notice I didn’t say carbohydrate quantity, the amount of total carbohydrate that you eat. I don’t think that’s the issue for most people. The issue is carbohydrate quality, and I know I’ve been beating this drum for a long time. I wrote about it in my book. Professor Spreadbury talks about it in the paper. He points to traditional cultures like the Kitavans and East African groups who eat from 35% to 70% of calories as carbohydrate, but all of these carbohydrates come from foods with living cells, like tubers or fruit or other plant parts, and the reason that industrialized diets are so harmful is not because of the overall amount of carbohydrates that they contain, as some people have argued, but because they don’t have those living cells, and as a result, they have a completely different impact on the gut microbiota than the ancestral carbohydrates, the real-food carbohydrates.

Steve Wright: Is it living, Chris? Or is it more of the complexity and the molecular structure of the differentiation? Because we can take those tubers and cook them. Now they’re not living anymore. But I was kind of under the understanding that you have a cell wall that contains all the parts of the cell and it’s a… complex isn’t necessary the perfect word here, but the actual molecule is still intact, whereas the processed foods, the molecule has been stripped down.

Chris Kresser: That’s right. Yeah, it’s been predigested, essentially, and broken down. And the cellular structure, like I said before, remains largely intact even during cooking, so the carbohydrates are locked into the fiber-walled cells, and that’s why in some cases the carbohydrate portion of that food is inaccessible, and that’s why it’s considered to be fiber. Fiber is not a nutrient technically for humans because we can’t absorb the carbohydrate that’s contained in those cells and make use of it ourselves, but those cells are instead nutrients for the bacteria that live in our large intestine because they survive in that form all the way down to the large intestine.

Another way to think about it is these real-food carbohydrates in these tubers and plant foods, especially the ones that are resistant to digestion, are not nutrients for us; they’re nutrients for our gut microbiota. On the other hand, the flour and sugar and processed starches, they are absorbed completely by us, and furthermore, they’re absorbed in a different part of the GI tract and they feed bacteria and can lead to an overgrowth of bacteria in that part of the digestive tract because they lack that cellular structure. And so they have a completely different impact on the gut microbiome. When you compare diets and you take one diet that has 25% or 30% of calories as carbohydrate in the form of these cellular carbohydrates, the tubers and the fruits and the vegetables, and then you have another diet that’s 30% of calories as carbohydrate in the form of flour and sugar, those are going to have a completely different impact on the body. And Spreadbury’s argument is the thing that’s mediating that difference in impact is the gut microbiome.

Steve Wright: Yeah. I love it. I believe it, too, and I think it just makes sense once you begin to actually think about what’s happening inside of the small intestine and the large intestine. When you really think about the structure of the foods we eat and what functionally is supposed to happen and then what is happening from an ecosystem in each organ, it only begins to take on just really logical sense.

Chris Kresser: I think that is a good point because we’ve been talking about this for a long time, but the contribution of this paper is that it provides a clear mechanism for why industrialized carbs have a different impact on the body than real-food carbs do. And to make it even more clear, the Standard American Diet varies from person to person, but on average it’s, I think, 40% to 45% of calories as carbohydrate, and so the low carb advocates have argued that, hey, this is way higher in carbohydrate and that’s why it’s problematic. Well, that’s not true, strictly speaking, because there are cultures, as I said before, that consumed an even higher percentage of calories as carbohydrate, up to 70%, but they didn’t have any of the diseases that people eating industrialized diets are suffering from, so that goes to show that it’s not about the total amount of calories from carbohydrate; it’s about the quality and type of carbohydrates that are being consumed.

Another example of this is that all of the studies that have been done on the paleo diet so far that have shown such remarkable improvements with weight loss and metabolic health have been done on a moderate carbohydrate paleo diet ranging from, I think, 20% to 30% or 35% of calories as carbohydrate. These are not really low carb diets that are being studied. They’re diets that restrict the quality and type of carbohydrates that are consumed. They eliminate processed and refined grains and all the dense, acellular carbohydrates that are part of the industrialized diet, and they just permit intake of starches and fruits and these cellular carbohydrates. I’m not aware of many, if any, studies on a very low carb paleo diet. Almost all the studies I’ve seen on paleo are 30% carbohydrate roughly, and you’re still seeing really remarkable reductions in weight and improvements in insulin sensitivity and body mass index and waist circumference and all that stuff, which really, again, just goes to support the argument that it’s more about the quality and type of carbs than the absolute amount.

Now, there is one thing that I want to point out, which is that — and you kind of alluded to this before, Steve — one reason I’m not a fan of very low carb, high protein, high fat diets for extended periods of time is that when you cut your carb intake, your absolute amount of carbohydrate that you eat, when you cut it down to below 10% or below 7%, which can be necessary in order to achieve ketosis for some people, it becomes very difficult to consume sufficient amounts of fermentable cellular carbohydrates to maintain a really robust and healthy gut microbiota. And I think this explains why some studies have shown that people consuming a very low carb diet may experience undesirable changes in their gut microbiota, and we have seen this in our clinic and in our work with patients. I think we need more research in this area, but again, if you understand — like you said, Steve — how the small intestine and the large intestine work and what the bacteria in the large intestine need to sustain themselves, it makes sense that if you’re on a diet where you’re eating on a percentage basis a much higher percentage of nonfermentable substrates, like meat and fat, and a much lower percentage of fermentable substrates, like the plant foods, then it very well could have an adverse impact on the gut microbiome over time.

Steve Wright: Yeah. I mean, we don’t know for sure yet, but the analogy I like to use is if you throw a scoop of peanut butter on the sidewalk in any city, you’re going to have a giant ecosystem that forms within minutes to hours, where a dog’s going to walk by, some ants, maybe a bird, maybe some humans will mess with it, who knows? And the same thing is true inside of our gut. Everything we put into our mouth, it is going to be part of the ecosystem. And some of those foods feed the ecosystem in certain parts of the body. Other foods feed the ecosystem lower in the body, in the large intestine, which is what we’re talking about here. So if you just start to think about the fact that everything you put into your body is sort of feeding this ecosystem… I don’t like getting reductionist, but it is kind of simple once you stop to think about how we do want a robust gut microbiome, and what feeds that? Well, certain types of foods. And other types don’t.

Chris Kresser: Exactly. And another angle or way to look at it is, like, in clinical practice, if I’m treating SIBO, one of the strategies that we use is a diet that’s low in fermentable fiber. We put patients on a diet that is low in these fibers because we know that these fibers can feed bacteria that have become overgrown in the small intestine. You know, there is a lot that we already know. We do need more research, but there is a lot that we already know. I mean, one of the treatments for SIBO, for example, is an elemental diet, which is composed of only simple carbohydrates, like glucose and fructose, that are absorbed extremely high up in the digestive tract and thus don’t become food for bacteria lower down in the gastrointestinal tract. And we know, studies have shown that people who are on elemental diets experience a dramatic shift in the composition of their gut microbiome. So I think you can make a very strong argument that a diet that’s low in fermentable substrates and high in meat and fat may have an adverse impact on the gut microbiome over time.

The Importance of the Context in Which You Eat Meat

Now, getting back to the original question, of course, when we tell patients to eat a paleo type of diet, we’re not necessarily — hopefully not — telling them to just eat only meat and fat. I mean, that’s not what the paleo approach is about, as we’ve talked about ad nauseam. We’re telling them to eat a diet that is very rich in fruits and vegetables and fermentable fibers and fermented foods and things that support the gut microbiome that also happens to include meats because meats are very nutrient dense and have a lot of other beneficial impacts on health, even if they don’t have, necessarily, a beneficial impact on the gut microbiota.

Again, to sum this up, it’s not really about whether you eat meat; it’s about the context in which you’re eating meat and the quality and the type of carbohydrates that you’re eating. You want to focus on real-food carbohydrates, like tubers and fruits and other plant parts, that contain all the fibers that feed beneficial gut microbes. This is resistant starch; we’re talking about non-starch polysaccharides, things like inulin and FOS and arabinogalactan. And then we’re talking about soluble fibers. All of these different types of fibers feed the beneficial gut microbiome.

I know that this is anathema to some people in the paleo community, but legumes can be a really good choice if you tolerate them, if you prepare them properly, soaking them prior to consuming them, and if they don’t replace more nutrient-dense sources of food. One of the reasons that they can be beneficial is they’re an excellent dietary source of resistant starch, which is somewhat difficult to come by in the diet.

And if you have to eat a very low carb diet or a ketogenic diet for any reason — maybe you’re treating a neurological condition, maybe you’re on a rapid weight loss program, maybe you feel better doing that in most ways — I would suggest increasing your intake of fermentable fibers. Many of these don’t really count towards your carb intake anyway because the carbs in them are not absorbed. For example, if you cook a white potato and you cool it, a lot of that will be resistant starch and it won’t impact the blood sugar or carbohydrate levels as much as if you just eat a cooked potato. You can use potato starch, and that, again, is not going to have an impact on your overall carb level intake. You can use plantain flour or green plantains, dehydrated, green banana flour. You can use supplements, non-starch polysaccharides. I saw one in my store called Prebiogen, which I really like. And then there are soluble fiber supplements, things like acacia fiber, or psyllium husk is another popular soluble fiber. Glucomannan is one that I like a lot. I think I also have that in my store. It has a particularly good effect on blood sugar. You can use all these fermentable fibers to make sure that you’re not starving your gut bugs of the foods that they need to thrive over the long term.

And I just had another thought along these lines. I can’t remember if I’ve ever blogged about this. I’m sure you’ve seen this study, too, Steve, but there’s now some speculation that a low FODMAP diet, which can be very therapeutic for people with IBS, irritable bowel syndrome, and also SIBO, may not be a good choice over the long term because it removes a lot of the foods that feed beneficial gut flora. This is being discussed now even in the mainstream scientific literature. That kind of supports everything that we’ve been talking about today.

Steve Wright: Oh, yeah, definitely. And I think the ways in which you’ve mentioned, and I would echo what you’ve seen, which is that if FODMAPs are an issue for you, obviously cut them out while you fix the root causes, and it’s an indication that your gut is really messed up. The more sensitive you are to FODMAPs, it appears that you’re having some definite issues. And then over time, you want to get those foods back in as fast as possible. That’s something that’s bugged me about that entire thing, so that’s cool that there’s some research and some talk about that finally.

Chris Kresser: Yeah, exactly. And I’m sure there will be more. We’re definitely moving in this direction.

OK, so that’s it for today. Keep sending us your questions. It’s fun to be able to hear what’s on your mind and respond to it, and I’ll look forward to talking to you next time.

Steve Wright: Yeah, send those questions in at ChrisKresser.com/PodcastQuestion. And in between episodes, hang out with Chris on Facebook.com/ChrisKresserLAc or Twitter.com/ChrisKresser. Thanks for listening, everyone.