August 15, 2018

The Gut-Brain Axis

An interview with Steven Sandberg-Lewis, ND, DHANP

This paper is part of NMJ's 2018 Microbiome Special Issue. Download the full issue here.

In this interview Natural Medicine Journal's editor-in-chief, Tina Kaczor, ND, FABNO, and Steven Sandberg-Lewis, ND, DHANP, discuss the integral role of the gut microbiota in mood and cognition. A review of how the gut and brain communicate through both the nerves and gut microbial metabolites is discussed. They also talk about how intestinal permeability and brain permeability are associated and what you can do about it. As a naturopathic clinician with over 40 years' experience, Sandberg-Lewis shares some clinically useful pearls along the way. 

Approximate listening time: 30 minutes

About the Expert

Steven Sandberg-Lewis, ND, DHANP, has been practicing since 1978, teaches gastroenterology at National University of Natural Medicine and has a private practice at 8Hearts Health and Wellness in Portland, Oregon. He lectures, presents webinars and interviews on issues of digestive health.

He is the author of the medical textbook Functional Gastroenterology: Assessing and Addressing the Causes of Functional Digestive Disorders, Second Edition, 2017. His column Functional Gastroenterology Bolus appears regularly in the Townsend Letter.

Within gastroenterology, Sandberg-Lewis has special interest and expertise in inflammatory bowel disease, irritable bowel syndrome, small intestine bacterial overgrowth (SIBO), hiatal hernia, gastroesophageal and bile reflux (GERD), biliary dyskinesia, and chronic states of nausea and vomiting. He lives in Portland with his wife, Kayle. His interests include mandolin, guitar, writing, and lecturing.


Tina Kaczor, ND, FABNO: Hello, I'm Tina Kaczor with the Natural Medicine Journal. I'm speaking today with Dr. Steven Sandberg-Lewis and our topic is the gut-brain axis. Dr. Sandberg-Lewis has been a practicing clinician for over 40 years now and he is the author of Functional Gastroenterology: Assessing the Causes of Functional Gastrointestinal Disorders, and that has come out in a second edition as of March 2017. He's also adjunct full professor at the National University of Natural Medicine. Dr. Sandberg-Lewis, thank you so much for joining me today.

Steven Sandberg-Lewis, ND, DHANP: You're welcome.

Kaczor: Alright, so I think our talk about the gut-brain axis is extremely timely because of the media attention now given to the bacteria and the effect of our microbiome on our physical ailments and I think it's beginning to look at how it effects the brain both cognition and mood as well.

And so, what I'd like to do is really start at the beginning and can you just give us a quick overview of what exactly do we mean when we talk about the gut-brain axis?

Sandberg-Lewis: Yeah, naturopathic medicine seems to always be at least 30 years ahead of the rest of medicine. We've been talking about this a long time but now we have a lot of research to back up what we talk about. So, the gut-brain axis probably has many more players than we're aware of but the ones we know about are, of course, the microbiota, a lot of people call that the 'microbiome'. But it's the bugs. About 100 trillion of them and they are, of course, not just in the colon but in the small bowel, in the stomach, which is not sterile and the oral and esophageal areas.

The true meaning of microbiome is the genome of the gut floor which has way more, at least 100X more genes than the human genome, which is 26,000. And when you put the two together, you call it the 'holobiome', which is the human genes and the microbial gene. But really, you need to do that because they interplay so much and the bugs really control our genome so intensely.

Then there's that whole genetic piece then there's all the, what we call the metabolon. What the bugs and the enteric cells make, all their metabolic products and that includes secretory IGA, short chain fatty acids, lipooligosaccharide, bacterial hormones and neurotransmitters and cytocinesis. We can talk about all those kind of details.

And then of course there's the enteric nervous system speaking to the vagus and the vagus speaking back. And there's the HPA axis and then there's the immune system and the gut. So, it's huge. It's so much talk it's deafening crosstalk.

Kaczor: It is interesting and one of the pleasures, I think, I've been practicing nearly 20 years and I know that you've been practicing over 40 years so, it's quite a long time to watch the evolution of thought processes in medicine as well as the population at large.

And in some of the folk medicine even, naturopathic medicine, but good old folk medicine, an apple a day and staying regular and keeping the bowels moving, it's amazing how that comes back at us and now we're talking about it in scientific terms which is fascinating to watch the pendulum swing.

Okay so, when we talk about how they communicate, you gave a little overview of some of the ways, when you mention the vagus system, what do you mean exactly?

Sandberg-Lewis: On every new patient, I like to have them open their mouth, stick out their tongue, take a look at their palatal arch and their uvula and then have them say 'ah'. When they phonate, we've all done this, check the vagus nerve. The place you can check the vagus nerve directly is there in the palate because the levator palatini muscles on either side raise the palate when you say 'ah' and when you phonate.

So, I'd like to see both arches go up symmetrically and not an asymmetrical rod. Occasionally you see nothing. The patient says 'ah', nothing happens. There's no palatal rise and you can have them do it over and over and nothing happens. So, that's a sign that the vagus isn't really firing the way it's supposed to and there are lots of ways to try and improve vegul tone. But that's a good thing to know about your patient.

The next thing is the vagus nerve gets sensory information from the enteric nervous system and the neuroendocrine cells in the gut as well as the epithelial cells. It gets input in actually 90% they assume, 90% of the crosstalk is from the enteric nervous system to the brain through the vagus.

So, it's mostly the gut talking to the brain and then the brain through the vagus talks back about 10% of the time. So, there's direct transmission through the nerves and then there's all the cytocinesis and other factors and neuro peptides that also speak through the humoral method.

Kaczor: So, what you're saying is the gut itself is sending signals through the vagus nerve to the central nervous system and effecting what exactly?

Sandberg-Lewis: So, yeah. It's pretty interesting what the gut is interested in talking about. Yeah, you wonder, what does my gut have to say? What does it care about? So, what the gut is saying, the 90% of impulse is going from the gut to the brain, it's talking about the shape and the consistency of the bowless of food moving through and scraping up against the ... rubbing up against the mucosa. The sheering forces of the bowless against the mucosa. That's stimulating serotonin locally but there's also this ... That's what the gut's interested in. Is, what kind of food is it, what's the shape, what's the consistency and what does it feel like as it rubs against the enteric cells?

This seems to stimulate taste receptors on the antero endocrine cells that are scattered throughout the mucosa and give information about the composition of the food, there's, again, there's all these neuro peptides and hormones, GI hormones that are released as well. But directly through the vagus nerve, we think it's mostly the gut talking about it's scratchiness of the food and the size and the consistency and the kind of food.

Kaczor: Okay. And I have to clarify for my own self, when you say 'taste receptors', you're going beyond the tongue? Is that what I hear you saying? Is this "taste receptors" that you say along the GI tract, how does that work?

Sandberg-Lewis: Air quotes, well, our genius in our midst, Paul [Calmens 00:08:18], he's been telling me for years that there are taste receptors throughout the entire gut. And especially most pronounced is the bitter, bitter receptors. And I've tried to go into the research and find out what exactly they do. We don't know a lot about what they do but we know that bitter receptors are not just in the tongue and the mouth, they're throughout the whole gut and they seem to trigger the release when they're stimulated. They trigger the release of ghrelin and glucagon peptide one which have to do with blood sugar balance and hunger and my guess is, Flip Wilson used to say, "The devil made me do it" when he did something that he thought was nasty.

But I really think that in many ways, the GI flora and the food that we eat interact to create cravings so that the body can get what it needs. And if you get more ghrelin, you get hungrier. And certain other, like GLP, maybe you're gonna create more sugar.

It's really important, of course, to eat food ... I think this is why Indies think it's so important to eat foods that's close to nature because once you get these synthetically modified foods or their consistency and their flavor and their compositions is altered, it probably throws off these natural mechanisms that tell us when to eat, when not to eat, when our blood sugar is fine, when it needs to go up or down. So, these are really finely tuned things.

Kaczor: Yeah, it's interesting in context, again, of traditional medicines because it automatically makes me think of Ayurvedic medicine and other traditional practices that naturally balance the flavors on the plate, that's a big part of making sure each meal is healthy in that tradition. So, let's talk about the microbiotas some more.

You mentioned briefly that its metabolites are part of the talk between the gut and the brain, can you elaborate on that?

Sandberg-Lewis: Yeah. First of all, I wanted to mention that the metabolic byproducts, the products of the microbiota, it's huge, it's huge. And Emerson Mayor's book, the gut-brain connection, he makes a quote that 40% of the metabolites in human blood are derived from gut flora, which blew my mind completely.

And so, I said, "Where is he getting that?" And I looked, I found it in two or three different articles. And so, to me, that means 40% of our blood chemistry is derived from the intestinal flora. And that makes sense since there are at least 10-to-1 more of them than there is of us in terms of cells. But I never really put that together.

So, there's these metabolites in our blood derived from the flora that do fine tuning of eating behavior, mood, blood glucose, digestive secretion, absorption, motility, just it's mind blowing. It's so important and it makes sense. You can understand that when you go ahead and even just take a broad spectrum antibiotic, we know that greatly increases the risk of kids and even adults, getting inflammatory bowl disease, especially Crohn's.

Just so many effects on immunity and the balance within the body if we knock down the bacteria or alter them or decrease their diversity. So, pretty important, pretty major stuff that everybody's been messing around with since the 1920s and '30s with antibiotics.

Kaczor: Mm-hmm (affirmative). Yeah and you mention a metabolite that caught my attention because I think it's at least in our naturopathic circles, we're paying a lot of attention to the role of that lipopolysaccaride and the LPS, for short. Can you talk a little bit about that? Because I feel like that's, as far as I can see, getting a bit of attention these days in how the gut and brain effect one another.

Sandberg-Lewis: Yeah well, I'm glad it's getting attention, it deserves it. You know, every physician knows about LPS in one particular way and that is, it is the cause of septic shock. It kills people if the LPS is high enough. What we don't usually hear about and we're starting to get more and more research on is, what about physiological levels of LPS when it's not super high?

Sandberg-Lewis: LPS is used in research, they inject it into lab animals to activate the NF kappa B pathway of inflammation and there's a tremendous amount of it. These are from the gram-negatives. The gram-positives also have an inflammatory precursor like this, which is the peptidoglycan. But, mostly we talk about the gram-negative because it's so potent and there were a million copies or so of LPS in each gram-negative microbe and it's not just something that gets emitted when the bug dies, it's also just when it's replicating or if you take an antibiotic and weaken it a little bit, they don't have to die to give off LPS.

And it's thought that in the adult human gut, you have up to a gram of LPS, a thousand milligrams at any one time. So, it's a major player. There's a lot of it and it can trigger the Zonulin pathway, which leads to intestinal permeability, hyperpermeability, which we know is related to autoimmunity and allergies.

Obese humans have up to a three fold increase in LPS compared to lean and maybe some of that also dove tails with the fact that obese adipose tissue has 10X as many macrofacies. So, you got a lot of esocine activity, a lot of TNF alpha.

Kaczor: Mm-hmm (affirmative).

Sandberg-Lewis: And different types of enteric flora have different amounts of LPS. Or even different potentiates. So, antero bacter are thought to have some of the most potent LPS that can be up to 1,000X more potent than some of the other gram-negative bacteria.

So, this is a major toxin, it's a major provoker of inflammation and preradical activity in all kinds of changes.

Kaczor: So, how does LPS effect the brain directly? Since, I hear what you're saying and I know even in experimental animals LPS is a common way to reliably instill an inflammatory process in a lab animal. So, it's clearly a very potent, inflammatory molecule. How does it effect the brain?

Sandberg-Lewis: So, the bacteria, we get some bacteria trans locating into the blood but they usually get called out after they travel through the portal vein to the liver by the cooper cells. At least if the liver's working well. You're not gonna have a lot of bacteria in the blood but the bacteria can still effect the central nervous system, even if they don't cross the blood brain barrier and never even get there.

First of all, one mechanism is that LPS and the inflammatory cytocinesis that it induces include interleukin one, interleukin six and I mentioned TNF alpha and they can actually up regulate the transcription of these cytocinesis in certain discrete areas of the brain.

And then one of the things that happens with that is, within the brain you get an up regulation of indoleamine dioxygenase, which is that enzyme that converts tryptophan to kynurenine and that can move further to quinolinic acid, which is neurodegenerative. Although, there's quinolinic acid, which is also has a positive effect.

So, depending on how it goes through the pathways, you can have neuro degeneration up regulated. And studies show that depression, anxiety and insomnia can issue from high levels of quinolinic acid. So, there's that.

There's also cognitive deficits and in my book, very important, is increased visceral sensitivity. All the functional disorders of the GI tract, there is increased visceral sensitivity meaning, people perceive their own motility and movement within the gut as pain or strong discomfort. And man, those patients are strong to treat because if you start to activate their GI tract and get it moving again after it's been atonic for years, then they're complaining that they're up all night with abdominal pain. And that's a tough one, we're trying to learn more about how to deal with visceral hypersensitivity.

But, it's thought that LPS is one of the things that triggers that too.

Kaczor: So, I have a two part question. I guess, in our clinical assessment of LPS, is there a means, I mean, I know that we could do testing for small intestine bacteria overgrowth through breath testing but, is there any blood test, I guess is what I'm thinking? Can you tack on any blood test to gauge LPS levels and the second part of this question is, what do we do about it?

I suppose treating the gut in a totality dysbiosis present, is the short answer. Any clinical pearls are certainly welcome.

Sandberg-Lewis: Yeah. So, you can, this is available, you can measure LPS. You can measure LPS binding protein, I believe as well. And you can, in your patients, you can, of course, measure zonulin, which gets up regulated by LPS. So, yeah. By all means, start experimenting with that and then see if you can get the levels down.

Now, yeah. I'm known for spearheading along with some other really busy physicians and researchers. The treatment and in our case, more the natural treatment, of small intestine bacterial overgrowth, you just can't get away from it. It's so key to, we used to say, "Death begins in the colon" when I was in school in the 1970s and now, I think it makes sense to say, "Dysfunction and autoimmunity begins in the small intestine". It's just associated with so much and that includes neurodegenerative diseases, like Parkinson's as well.

A practical thing, yeah. Learn how to test for, interpret and treat ... Use your testing and learn how to treat SIBO. Both the hydrogen, methane and hydrogen sulfide types. And don't throw out the yeast with it either because they often go together and get that metabolite base 40% of the blood. Get it into a functional mode instead of a dysfunctional mode.

Kaczor: Mm-hmm (affirmative). Mm-hmm (affirmative). Yeah. And I know, I will say that, you lecture and write a lot on the clinical aspects of this. So, anyone who wants further information can certainly start Googling you and find lots and lots to followup on. I do want to ask another question because this issue that we are in for the Natural Medicine Journal this month is a special on the microbiota and the microbiome. How do probiotics specially affect the gut-brain axis?

Sandberg-Lewis: I don't know that we have enough yet to really have a great answer. Although, there are some docs out there that really have a strong handle on the strain specific effects of probiotics and people like Jason Hawrelak who is an ND and teaches at Western States and practices in Australia, he has totally got that covered. So, I would highly recommend looking at his website Jason Hawrelak, Hawrelak. But I mean, we know that there are studies that show that fermented foods significantly reduce anxiety, especially social anxiety.

And there's a lot more research going on on strains, specific things that show that there are specific effects on anxiety and depression. But it's still really early so, I can't say I have a really good picture of that. When people ask me about probiotics, I usually say, "I don't know anything about probiotics". They don't believe me but, yeah.

Kaczor: So, is it accurate to say that you advocate the whole foods diet, plenty of prebiotics in the form of fibers and resistant starches and things like that and then trust that if that is done well and consistently and then, of course if there is other treatments to kill undesirable bacteria etc. but complimenting ... I mean, the way to encourage the good bacteria is to give the prebiotics more in your view?

Sandberg-Lewis: Well, the problem is a lot of my patients, because they have overgrowth, they can't tolerate prebiotics and fiber. So, when I first start working with them, we can't really use those things except very specific types. We know that partially hydrolyzed program seems to be actually beneficial for people who have overgrowth, sometimes used along with rifaximin in treatment of hydrogen SIBO and it increases the effectiveness of that.

But, there's some GOS's that that may also be well tolerated. But that's a problem in the beginning because if you have overgrowth and then you feed them with a prebiotic, then it just increases symptoms and problems. So, it's a fine balance, it's a fine balance. But, yeah. I really encourage my patients to eat whatever fermented foods, probiotic foods that they tolerate.

So, we use lactose-free, fermented dairy products, we use pickled items like kimchi or sauerkraut, the real stuff not the fake stuff. The refrigerated kind. Or homemade. And things like that. I think all traditional groups of people around the world have their own probiotic foods. Some of them pretty hard to even relate to, like haggis in ... where is that? Scotland. Where they eat the goat stomach that's fermented. Fish and rotten fish in the northern areas of Europe.

There are some really interesting things you'd think, "Why the hell would people ever invent that food?" But these things have tremendous fermentative capabilities. And one thing that I'm sure NDs understand this but it comes up a lot with patients asking, they'll say, "So, you don't want me to eat any fermented food, right? Because I already have ... You want me on a low fermentation diet". And I say to them, "Well, no that's not what I want you to do". Unless you have a histamine sensitivity and you can't handle foods that are fermented, I want you to use those things because if you eat a high fermentation diet that has carbohydrates that are easily fermented, that produces gases. Hydrogen, carbon dioxide, maybe ethanol, methane, hydrogen sulfide in the gut and causes distention and pain and changes the stools and can cause bloating.

But if you eat a food that is a fermented food, the gases have already come off into the atmosphere in the process of fermentation and now you're just getting all the bacteria and the great metabolites without the gas that causes the symptoms. I think that's an important differentiation.

Kaczor: Well, yeah that's a great way to put it. To help them and us understand it a little bit. One last question, we'll end on a fun question, when you hear the term 'gut reaction to something', because we're talking about the gut-brain axis and someone says, "I used my gut" or gut instinct, gut reaction, what do you think?

Sandberg-Lewis: Well, I'll bet physicians with different backgrounds have different ways of interpreting that but clearly if 90% of the input in the gut-brain axis is coming from the gut and if you think about it, if virtually every neuro peptide and GI hormone that's produced in the gut effects insulin and blood sugar and we know the brain suffers within minutes from blood sugar that's too low whereas the other organs may not care for quite some time and oxygen as well, of course, to the brain within three minutes.

There are major effects on life and death related emotions that take place when the gut is feeling like something is wrong and it's gonna make more jittery molecules instead of more serotonin and gaba.

And that's gonna have very rapid effects on the mood and on the functioning of the person's nervous system.

Kaczor: Mm-hmm (affirmative). Alright well, I sure do appreciate the time you took to talk to us today about this. It is a huge topic and I am excited, as a naturopath that everything is coming back to a source, the GI tract, I mean and we've always been taught that we have to remedy the gut and get that in order before we can really keep someone in an optimal health state.

So, sometimes that's harder than others and I do appreciate the time it took to enlighten us today with the gut-brain axis and it look forward to talking to you probably in the realm of gastroenterology again in the future.

Sandberg-Lewis: Great, let's do it.

Kaczor: Alright, take care.

Sandberg-Lewis: Alright, bye.

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