Recap: How your gut fuels your brain and mood | Prof. John Cryan

Summary

Summary of "Recap: How Your Gut Fuels Your Brain and Mood" Featuring Prof. John Cryan

Podcast: ZOE Science & Nutrition
Host: Jonathan Wolf
Guest: Professor John Cryan
Release Date: July 29, 2025

In the episode titled "Recap: How Your Gut Fuels Your Brain and Mood," host Jonathan Wolf engages in an enlightening discussion with Professor John Cryan, a leading expert on the gut-brain axis. The conversation delves deep into the intricate relationship between our gut microbiome and brain health, exploring how microbes influence our mood, memory, and overall neurological function.

1. Introduction to the Gut-Brain Connection

The episode begins with an overview of the evolving understanding of the brain's interaction with the rest of the body. Traditionally viewed as an isolated organ, recent research has illuminated the significant role of the gut as a "second brain."

Professor John Cryan [00:54]: "There is now concrete evidence that the composition of the microbes in your gut influences brain development, influences brain function, and can help steer the brain in specific ways."

2. Understanding the Gut-Brain Axis

Professor Cryan elaborates on the concept of the gut-brain axis, explaining how signals from the gut communicate with the brain to influence behavior and physiological responses.

Professor John Cryan [03:54]: "The gut brain axis has been long, long known. It's basically how signals from your gut go to your brain to change your behavior."

He emphasizes the addition of the microbiome as a crucial component in this communication pathway, highlighting that microbes have always been integral to our physiology.

3. Animal Models and Microbiome Research

The discussion transitions to the use of animal models, particularly germ-free mice, to study the impact of the microbiome on brain development and behavior.

Professor John Cryan [01:20]: "Mice that have grown up without any bacteria in their gut, their brains don't develop normally."

He explains the significance of these findings, noting that absence of microbes leads to altered brain functions, such as impaired social behavior and abnormal stress responses.

4. Communication Pathways Between Gut and Brain

A significant portion of the conversation focuses on the mechanisms through which the gut and brain communicate. Professor Cryan identifies the enteric nervous system and the vagus nerve as primary conduits for this interaction.

Professor John Cryan [06:46]: "We have the enteric nervous system… it's a really good conduit for signaling directly to the brain."

Professor John Cryan [07:24]: "When you cut the vagus nerve in a mouse model, we severed all of the effects of a specific Lactobacillus bacteria on brain and behavior were gone."

These insights underscore the physical pathways that facilitate the gut's influence on neurological processes.

5. Impact of Diet and Lifestyle on the Microbiome

Professor Cryan provides practical advice on maintaining a healthy microbiome to support brain health. Key recommendations include:

• Increase Prebiotics: Emphasizing fiber-rich foods to nourish beneficial gut bacteria.

  Professor John Cryan [10:00]: "Fibers in particular will be really, really important."

• Incorporate Fermented Foods: Such as kimchi, kefir, and kombucha to enhance microbial diversity.

• Consume Polyphenols: Found in onions, grapes, nuts, and green tea, which support microbial health.

  Professor John Cryan [09:45]: "Polyphenols are really good… they're broken down by microbes and can be broken down to chemicals that are important."

• Limit Processed Foods and Artificial Sweeteners: These can negatively impact the microbiome.

• Engage in Aerobic Exercise: Beneficial for both microbiome diversity and brain function.

He also touches on the importance of circadian rhythms, sleep quality, and the mode of birth (favoring natural birth over Caesarean sections) in shaping a healthy microbiome.

6. Microbiome Across the Lifespan

The conversation explores how the microbiome evolves from infancy through old age, affecting brain health at each stage.

• Early Life: The first two years are critical for microbiome stabilization, closely linked to diet and environment.

• Adolescence: The brain undergoes significant pruning and development, with emerging evidence suggesting microbiome influence on these processes.

  Professor John Cryan [13:01]: "The adolescent brain is still under construction… There's a lot of what we call pruning."

• Aging: Aging adversely affects the microbiome, impacting brain health. Interestingly, introducing young microbes has shown potential in reversing some age-related brain declines.

7. The Role of Pets in Microbiome Health

Professor Cryan discusses emerging research suggesting that pet ownership, particularly dogs, may positively influence the human microbiome, thereby benefiting behavior and mental health.

Professor John Cryan [11:48]: "Having a pet and particularly a dog is good for your microbiome… it’s an intriguing area overall."

However, he notes that more research is needed to fully understand this relationship, especially in older populations.

8. Conclusion and Final Insights

The episode wraps up with an affirmation of the profound impact the gut microbiome has on brain function and overall health. Professor Cryan underscores the importance of nurturing our microbial communities through mindful dietary and lifestyle choices to support both gut and brain health.

Professor John Cryan [12:55]: "The increase in diversity of foods and Mediterranean style diets are really good for your microbes, so therefore they should be also good for your brain."

Key Takeaways

• Gut-Brain Axis: A bidirectional communication system where the gut influences brain function and behavior.

• Microbiome's Role: Essential for normal brain development and function; imbalance can lead to neurological and behavioral issues.

• Practical Steps: Incorporate prebiotics, fermented foods, polyphenols, and regular aerobic exercise while limiting processed foods to maintain a healthy microbiome.

• Lifelong Impact: The state of the microbiome at different life stages significantly affects brain health and cognitive functions.

This episode provides a comprehensive exploration of how our gut microbiome serves as a cornerstone for brain health, offering actionable advice to optimize this intricate relationship for improved mood, memory, and overall neurological well-being.

Transcript

[Zoe]

Hello and welcome to Zoe Recap, where each week we find the best bits from one of our podcast episodes to help you improve your health. Today we're exploring the connection between your gut and your brain.

[Host]

For years, the brain was seen as.

[Zoe]

Somewhat detached from other parts of our body, working in isolation above all else. However, emerging research is flipping our idea of the brain on its head. Scientists now know that the gut acts like a second brain, influencing everything from our mood and memory to our risk of neurological disease. So have we been neglecting a vital piece of the brain health puzzle? Joining me to unpack this topic is Professor John Kryan, a world leading expert in the gut brain axis. He's here to explain how the two communicate and what you can do to support that connection.

[Host]

Are there links between the gut and the brain?

[Professor John Kryan]

What we know now, and there's been an evolution over the last two decades, I would say, is that there is now concrete evidence that the composition of the microbes in your gut influences brain development, influences brain function, and can help steer the brain in specific ways. The evidence is coming largely from studies in animal models.

[Host]

And John, just to make sure, everyone has said an animal model, what does that mean?

[Professor John Kryan]

Usually a mouse or a rat. So because we can get mice that can grow up without microbes ever having a microbe, you know, if you want to find out if something is important in a process, we know from engineering or other areas of biology that if you take it out and see what happens, it's probably one of the best ways to see if it's important. So mice that have grown up without bacteria, they allow us to answer the question, is the microbiome relevant? Yes or no. And studies from our lab and from other labs over the past decade or more have shown that in these mice that grow up without any bacteria in their gut, that their brains don't develop normally.

[Host]

That's amazing. And do you find special mice that you found somewhere in the world that grew up without any gut microbiome? Is that how you compare this?

[Professor John Kryan]

No. This is an unusual lab based situation. So these animals are kept in this ultra sterile condition where they've never been exposed to microbes. And this concept goes back to Louis Pasteur. He first tried to do these work with these types of mice and they are not really translatable to anything human, with maybe the exception being the boy in the bubble that Paul sang about in the 1980s. These mice in the bubble, they allow us to have this specific question, is the microbiome involved? Yes or no?

[Host]

Got it. So it's quite unnatural, is what you're saying. You have to create this incredibly sterile situation because we're constantly surrounded by these bacteria who want to get into us and presumably these mice. So you create this incredibly sterile situation to discover what happens if a mammal grows up without any bacteria. And that's what you're comparing then with the normal situation for mice and I guess for us. Right, which is we're stuffed full of trillions of them.

[Professor John Kryan]

Absolutely. And our group and the group of Rochelle Heights in Karlinska and Jane Foster in McMaster well over a decade ago, all showed roughly around the same time, that these mice have messed up brains in different ways in terms of their behavior. They respond differently to stress. We showed that they don't have proper social behavior, that they don't have proper fear learning, and their pain processing is different. So they've given us a real entry point into convincing us that there's something about microbes and brain function that we need to pay more attention to. And that's taken us on this journey that my lab has been on for well over a decade.

[Host]

And, John, one of the words that I think we often hear is like gut brain axis, which is a great sort of phrase, which I don't really understand what it is, but I'm hoping you're about to explain. Is that this or is that something different?

[Professor John Kryan]

Well, yeah. So the gut brain axis has been long, long known. It's basically how signals from your gut go to your brain to change your behavior. Now, that's been very well studied in the context of food intake, because we take food into our bodies, but the reason we do that is in response to hunger. Signals that come from our brain, and then we take it in, and then we stop eating based on signals that are telling us we're full, and they are also brain derived. And so the gut brain axis has been around for a long time, mainly in that context. Then people started being more understanding that disorders like irritable bowel syndrome, which is a very common unloved disorder associated with abdominal pain and bloating and various other functional side effects, that this is really a disorder of how our gut and our brains talk to each other. What we now think of is a microbiome, gut brain access. So the microbes are the new players. So it makes things even more complex. And what we're trying to do figure out is how do the microbes in the gut talk to the aspects of gut brain signaling to change brain and behavior? So it's a new dimension, a new Player, if you will. We have to think that the microbes were there first. And so that's an important aspect of all of this in our learnings from an evolutionary perspective, microbes were there. And so there's never been a time where our brain or our gut existed without microbial signals. So we kind of have to contextualize that. And we, we're very human focused in our primacy of what's the most important. But we have to remember also that the mitochondria, the powerhouses of cells, are actually microbes that got lost into the cells. And so there's such a close relationship between our microbes and everything through evolution. And so once you start contextualizing it in that way, it's probably not surprising that the microbiome could play such a key role in so many aspects of our physiology and our behavior.

[Host]

So just to make sure I got that, what you're saying is, hey, the microbes were there before there were any human beings, in fact, before there were any mammals. And so, you know, even from the very beginning of building this gut, there would have been microbes there. So it's hardly surprising that they are a sort of built in feature, if you like, of our body rather than how, you know, I think we obviously all thought about them until a few years ago as a sort of in irrelevance.

[Professor John Kryan]

Yeah, absolutely.

[Host]

So I think lots of listeners have asked this question about, well, how does that work? Because I think they can understand that your microbes affect the way you digest your food. They're in the same place. That makes sense. But you know, my gut and my brain are in two different places. Bacteria are really small. How do these bacteria affect what's going on in my brain? And I know this is something that you study.

[Professor John Kryan]

Yeah. And it's a large part of what our lab is focused on is really trying to delineate the mechanisms and pathways for this communication. And there are a number of ways. First of all, it's worth noting that within our gut we have a second brain. This is called the enteric nervous system. And this second brain has more nerve cells than our spinal cord. Enteric nervous system is very important for digestion, motility, various aspects of gut function. But it's also a really good conduit for signaling directly to the brain. So that's an important first pass on it. The second thing is we have a nerve. It's one of the major cranial nerves which sends signals from the brain to all the organs and from organs back up to the brain. It's called the vagus nerve. Now, vagus comes from the Latin for wandering. It's the same derivation as vagabond or vagrant. And this nerve is really well, poised to be an important highway of communication between the gut and the brain and between the microbes and the brain. And so over a decade ago, we showed together with the late John Beanstalk's lab that when you cut the vagus nerve in a mouse model, we severed, all of the effects of a specific Lactobacillus bacteria on brain and behavior were gone. So, as I like to remind people, this tells us that what happens in Vegas doesn't just stay in Vegas, but will actually affect our emotions in certain ways.

[Host]

Okay, I love that. So I've got a vagus nerve inside me, which bit like Vegas, all sorts of bad things can happen and come back to haunt me afterwards. How would you think about what people should be doing either for themselves or as they're thinking about their children or. Or relatives?

[Professor John Kryan]

The important thing is to realize that your microbiome changes as you navigate life naturally. There's a natural change overall. In early life, it takes about two years for stability to start to come in. And it's really primed to maximize what it can get from milk overall and then into adolescence. There's less studies, but we're beginning to see more and more relationships between the microbiome and then we get a stable microbiome unless we shift our environment. And then as we age, then we see a deleterious effect of aging on the microbiome, which we've been showing, for example, that that affects brain health. So we've been able to take the microbes from young animals and reverse the effects of aging on brain health. And that's been quite remarkable. So we know that we need to mind our microbes for optimal brain health. And so some of the practical things that I would tell people to do, that has some evidence, although we could do it more. So there are certain things to enrich in your diet, which is increasing the levels of prebiotics. Fibers in particular will be really, really important. Fermented foods, the 3Ks of kimchi, kefir and kombucha, but there's loads of other fermented foods. And throughout the world, we have a rich cultural history of fermented foods. And not so much in Ireland, I would say, but in other places. But studies like from Justin Sonnenberg's group and now more recently from our own, has shown that there's a science of biology, how these fermented foods are interacting with the hosts to have positive effects. So really, really doing that. We know color is great. Polyphenols give lots of foods color. And polyphenols are broken down by microbes, but they also act on microbes and they can be broken down to chemicals that will be really important. So heavily present in things like onions and grapes and nuts and also in green tea. And people often talk about it in the context of red wine, of course, but it's also in grape juice. But polyphenols are really good. There's been an increasing interest in polyunsaturated fatty acids. So These are the PUFAs that are very good for how membranes and cells work, but they also can have effects directly on the microbiome. And so maybe some of the positive effects of these polyunsaturated fatty acids may be really good. And then there are things we should avoid in our diet as much as we can, and that's the processed food. Artificial sweeteners in particular have been shown to have consistently negative effects on the microbiome. Overall. We know that certain lifestyle other factors can influence the micro microbiome. So our sleep and our circadian rhythms and jet lag all has effects. So we need to be careful on that. Exercise in particular, aerobic exercise has been shown to have really good effects on the microbiome and potentially then onto brain function overall mode of delivery at birth. So we should as a public health should be really encouraging more people to if they can give birth naturally as opposed to by C section because there's enduring effects of C section on the microbiome that can potentially translate to behavior in later life. And then finally there's great data now accumulating from population wide studies that having a pet and particularly a dog is good for your microbiome. And probably maybe some of the beneficial effects of companion dogs on behavior may be related to their effects on the microbiome and gut brain signaling. That needs to be figured out. But I think it's really intriguing area overall.

[Host]

I just want to pick up on this sort of older age thing. So if you're listening to this and you want to maintain your brain health, which I think is becoming increasing focus for many people, right as we age and we see all of these problems. Is there anything specifically within that or on top of that that you need to do, should they all be immediately going out and getting a pet, is that the key additional activity?

[Professor John Kryan]

Well, it's interesting. A lot of the pet work is coming from early life studies. So there hasn't been much data that I'm aware of in older people right now. And we know that social interactions themselves. By living with someone else, your microbiome starts to shift and change. The best studies on old age then have shown that things like the diversity in the diet is what gives the best health outcomes in the context of frailty and other medical outcomes. There's been no reasonably good data yet on brain function as we age in humans. But the studies like the New Age study and the elder Met studies, which would really support this increase in diversity of foods and Mediterranean style diets are really good for your microbes, so therefore they should be also good for your brain.

[Host]

That makes sense. And what about adolescence? I think you talked about like a big shift going on in the brain at this point.

[Professor John Kryan]

So the adolescent brain is really a brain that's still under construction. We often forget that our brain goes through quite remarkable changes during this period. And basically it's a period where the brain has to decide what to keep for the rest of life. So there's a lot of what we call pruning. So synaptic pruning, where basically our immune cells are saying, okay, keep or not keep. What's going to be essential for what need to keep you going?

[Zoe]

As you can imagine hosting this podcast, running Zoe, juggling family life, it all keeps me pretty busy. So I try as best I can to stay energized and show up well in all those parts of my life by fueling my body with the right food, by exercising, and by adding a scoop of daily 30 to my meals every day. If you haven't heard of Daily 30 yet, it's the gut supplement designed by our gut health scientists here at Zoe. It's made of over 30 high quality hand picked plants, including seaweed, fungi and different types of fiber. Better yet, it contains ingredients that support gut health, digestion and energy, which is ideal for packed calendars and busy lives. Simply add one scoop a day to any meal for an extra boost of fiber and plant diversity. And because it tastes delicious on just about anything and adds a satisfying crunch, it quite quickly slots into your life, becoming a daily healthy habit you'll always have time for. By the way, whenever we talk about Daily 30 as a good source of fiber, we're required to say that it contains 4 grams of total fat per serving. Obviously, that's all amazing healthy fats from plants, so order yours [e-mail] daily30. Thanks for listening and see you next time.

[Professor John Kryan]

It.