What we know about the so-called "gut-brain axis" — and what we don't.
By Cassie Shortsleeve, Men’s Health
May is Mental Health Awareness Month. For too long, men have been silent about mental health and it’s literally killing us. We can change that. Our Healthy Mind, Healthy Body series shines a light on mental health issues that everyone should be talking about. Share your own moment of #HowIGotHelp and let your voice inspire other people's.
May is Mental Health Awareness Month. For too long, men have been silent about mental health and it’s literally killing us. We can change that. Our Healthy Mind, Healthy Body series shines a light on mental health issues that everyone should be talking about. Share your own moment of #HowIGotHelp and let your voice inspire other people's.
- There are trillions of bacteria in your gut that help you digest your food and keep your immune system in check
- It's well-established that gut bacteria plays a tremendous role in your overall health, but an emerging body of research indicates that it could play a role in mental health as well
- Some people have claimed that changing their diet and taking probiotic supplements has helped them manage their symptoms of anxiety and depression
- But how much do we actually know about the link between gut health and mental health to begin with?
When Emeran A. Mayer, M.D., was in med school in 1973, he spent a summer working in the digestive disease division at Mass General Hospital in Boston. It was there where he noticed something that would change his career. “Many patients were admitted to investigate chronic abdominal pain symptoms, but diagnostic exams were negative,” he says. “Taking a history of patients, it became clear to me that many of these patients had increased anxiety, depression, and stress levels.”
When Mayer, who went on to write the book The Mind-Gut Connection, began his research, the relationship between gut health and mental health was a fairly niche area of medicine. But today, researchers are now starting to fully understand what he'd observed back in the 1970s: that changes in your gut bacteria could lead to changes not only in your immune and nervous system, but also in your brain, potentially playing a role in mental health issues like anxiety, depression, stress, and fear.
The so-called "gut-brain axis" (also known as the "gut-brain connection" or “mind-gut connection”) is a major part of the health vernacular, to the point that some psychiatrists have started recommending probiotic supplements to patients. Some people have even claimed that changing their diet and taking probiotics helped them “cure” their anxiety and depression. Taking probiotics and prebiotics "gave me my life back," one woman with a history of anxiety attacks wrote on Reddit.
But how much do we actually know about the relationship between gut health and mental health? Here's how the bugs in your gut and your mind are connected — and what scientists on the front lines hope is next.
When Mayer, who went on to write the book The Mind-Gut Connection, began his research, the relationship between gut health and mental health was a fairly niche area of medicine. But today, researchers are now starting to fully understand what he'd observed back in the 1970s: that changes in your gut bacteria could lead to changes not only in your immune and nervous system, but also in your brain, potentially playing a role in mental health issues like anxiety, depression, stress, and fear.
The so-called "gut-brain axis" (also known as the "gut-brain connection" or “mind-gut connection”) is a major part of the health vernacular, to the point that some psychiatrists have started recommending probiotic supplements to patients. Some people have even claimed that changing their diet and taking probiotics helped them “cure” their anxiety and depression. Taking probiotics and prebiotics "gave me my life back," one woman with a history of anxiety attacks wrote on Reddit.
But how much do we actually know about the relationship between gut health and mental health? Here's how the bugs in your gut and your mind are connected — and what scientists on the front lines hope is next.
What is the gut-brain axis?
The trillions of bacteria in your gut make up what’s known as the gut microbiome. They are, more or less, your friends, helping you digest food and keep your immune system in check, explains Glenn Treisman, M.D., Ph.D., a professor of psychiatry and behavioral sciences at Johns Hopkins University School of Medicine.
“The digestive system, and specifically the intestines and their resident bacteria, are playing an incredible role in keeping the body healthy,” says David Perlmutter, M.D., editor-in-chief of the upcoming scientific textbook The Microbiome and the Brain.
But your gut doesn’t just play a role in your physical health. The gut-brain axis is a bidirectional communication system between the gut microbiome and your brain. Put simply, your brain sends signals to your gut via your body’s control system, the autonomic nervous system. Your gut also talks to your brain via hormones that are stored in specialized gut cells, immune molecules, and nerve signals, Mayer says. “These communication channels make the gut and the brain the two most closely connected organs within our body,” he says.
Some studies have suggested that humans with brain disorders like Parkinson’s disease and Autism spectrum have altered composition and function of their gut microbes. “The gut is critically involved in regulating inflammation, the underlying mechanism related to our most dreaded brain conditions like Alzheimer's disease, Parkinson's disease, and multiple sclerosis,” says Perlmutter.
“The digestive system, and specifically the intestines and their resident bacteria, are playing an incredible role in keeping the body healthy,” says David Perlmutter, M.D., editor-in-chief of the upcoming scientific textbook The Microbiome and the Brain.
But your gut doesn’t just play a role in your physical health. The gut-brain axis is a bidirectional communication system between the gut microbiome and your brain. Put simply, your brain sends signals to your gut via your body’s control system, the autonomic nervous system. Your gut also talks to your brain via hormones that are stored in specialized gut cells, immune molecules, and nerve signals, Mayer says. “These communication channels make the gut and the brain the two most closely connected organs within our body,” he says.
Some studies have suggested that humans with brain disorders like Parkinson’s disease and Autism spectrum have altered composition and function of their gut microbes. “The gut is critically involved in regulating inflammation, the underlying mechanism related to our most dreaded brain conditions like Alzheimer's disease, Parkinson's disease, and multiple sclerosis,” says Perlmutter.
"The gut and the brain [are] the two most closely connected organs within the body."
So how does mental health come into play? The gut bacteria can also produce neurotransmitters such as serotonin and dopamine, which play a role in mood regulation. It’s a back-and-forth sort of relationship. “The brain does things that affect the gut bacteria, and gut bacteria do things that affect the brain,” says Treisman.
Indeed, a rapidly growing body of research suggests that altering your gut microbiome can impact mood, as well as various mental health conditions. Take a 2017 study published in the journal Microbiome, which found that, in mice, gut microbes appeared to influence brain molecules called microRNAs, which can impact how genes are expressed in the body. Scientists also believe that dysfunction of microRNAs could contribute to stress- and anxiety-related disorders. Another study led by John F. Cryan, Ph.D., a professor and chair of the department of Anatomy & Neuroscience at the University College Cork in Ireland, found that a specific strain of bacteria (B. longum 1714) subtly decreased stress responses in healthy people.
On the surface, such results might be enough to make the estimated 16 million and 40 million U.S. adults who suffer from depression and anxiety disorders invest in a bottle of probiotics. But researchers say not so fast.
Can we really use probiotics to help treat mental illness?
The short answer: we don’t know.
Up until recently, most of the research, such as the 2017 Microbiome mice study, have been conducted in animals, and mice and humans don’t always have that much in common. Plus, Treisman says much of the research on the brain-gut connection is too preliminary to determine cause and effect. He likens the connection between the gut microbiome and the brain to a bridge: “we’ve started the bridge from both sides and we’ve made some progress. But we don't know how it hooks up,” he says.
We do, however, know that there's a complicated set of arrows from your gut to your brain. Most research suggests that everything from the outside environment and where you live to medications you might be on, lifestyle choices, and genetics can lead to changes in your gut microbiome, altering levels of inflammation throughout your body, up to and including your brain. Your diet is just one of those many factors.
So as for those packaged probiotics promising that they can give you a good mood now? Sorry, but Mayer notes that “there is currently no solid scientific evidence to support the administration of probiotics for mental health.” There’s a lot more research needed to hammer out precisely how the gut-brain connection works.
Up until recently, most of the research, such as the 2017 Microbiome mice study, have been conducted in animals, and mice and humans don’t always have that much in common. Plus, Treisman says much of the research on the brain-gut connection is too preliminary to determine cause and effect. He likens the connection between the gut microbiome and the brain to a bridge: “we’ve started the bridge from both sides and we’ve made some progress. But we don't know how it hooks up,” he says.
We do, however, know that there's a complicated set of arrows from your gut to your brain. Most research suggests that everything from the outside environment and where you live to medications you might be on, lifestyle choices, and genetics can lead to changes in your gut microbiome, altering levels of inflammation throughout your body, up to and including your brain. Your diet is just one of those many factors.
So as for those packaged probiotics promising that they can give you a good mood now? Sorry, but Mayer notes that “there is currently no solid scientific evidence to support the administration of probiotics for mental health.” There’s a lot more research needed to hammer out precisely how the gut-brain connection works.
"We’ve started the bridge from both sides, but we don't know how it hooks up."
The future of psychobiotics
For the sake of argument, however, let’s assume that one day, scientists will be able to ID specific microorganisms that, when introduced to the human gut, have beneficial effects on mental health. The next step would likely be prescribing prebiotic (a type of fiber that your gut microbes eat) or probiotic supplements to improve your gut health and, in turn, your mental health.
Known as psychobiotics, this emerging scientific field is still in its infancy. But in coming years, Treisman argues experts may even be able to make a link between a particular health condition and the presence of a certain kind of gut bacteria. This would theoretically allow doctors to offer a "microbiome" prescription for better health. “We’re excited about that, but we’re not there yet,” he says.
There is, however, one big caveat: gut bacteria varies tremendously from person to person, so a certain kind of probiotic or food that makes you feel great might make someone feel crummy. It will likely be difficult to recommend a course of treatment that works for multiple patients. “It’s not like everybody has the same bugs,” says Treisman.
Known as psychobiotics, this emerging scientific field is still in its infancy. But in coming years, Treisman argues experts may even be able to make a link between a particular health condition and the presence of a certain kind of gut bacteria. This would theoretically allow doctors to offer a "microbiome" prescription for better health. “We’re excited about that, but we’re not there yet,” he says.
There is, however, one big caveat: gut bacteria varies tremendously from person to person, so a certain kind of probiotic or food that makes you feel great might make someone feel crummy. It will likely be difficult to recommend a course of treatment that works for multiple patients. “It’s not like everybody has the same bugs,” says Treisman.
So what can you do to improve your gut health/mental health?
Generally speaking, if you struggle with mental health issues, your first move should be to seek professional help (and we have a complete list of mental health resources for you here). You can speak with your mental health care provider about a course of treatment that works for you.
But if you've already established a primary course of treatment, and you’re just looking to make small tweaks to your lifestyle, try paying closer attention to how certain foods make you feel, suggests Treisman — a sign, perhaps, that that all those little microbes in your gut are trying to talk to you.
Additionally, some research has shown a link between depression and eating too many processed foods; other studies have found that people with depression have a less diverse microbiome, says Cryan. “For appropriate brain and psychological health, we strongly advocate a diverse diet,” he says.
That means eating fruits and vegetables full of polyphenols and antioxidants, such as blueberries, peppers, turmeric, and olive oil. Researchers have also suggested that a Mediterranean-style diet (meaning a focus on vegetables, fruits, nuts, seeds, legumes, potatoes, seafood, and extra virgin olive oil) has been linked to a better mood — something that, perhaps, is brought about by changes in the gut microbiome.
Bottom line? We’re not yet at the point where scientists can specifically indicate a cocktail of probiotic organisms for specific mental health conditions. But if you do want to improve your general gut health, Perlmutter notes that probiotic foods — kimchi, sauerkraut, yogurt, and kefir — have been shown to reduce inflammation, while prebiotics — garlic, onions, leeks, chicory root, dandelion greens, Jerusalem artichoke, and jicama — can also nurture good gut bacteria.
But if you've already established a primary course of treatment, and you’re just looking to make small tweaks to your lifestyle, try paying closer attention to how certain foods make you feel, suggests Treisman — a sign, perhaps, that that all those little microbes in your gut are trying to talk to you.
Additionally, some research has shown a link between depression and eating too many processed foods; other studies have found that people with depression have a less diverse microbiome, says Cryan. “For appropriate brain and psychological health, we strongly advocate a diverse diet,” he says.
That means eating fruits and vegetables full of polyphenols and antioxidants, such as blueberries, peppers, turmeric, and olive oil. Researchers have also suggested that a Mediterranean-style diet (meaning a focus on vegetables, fruits, nuts, seeds, legumes, potatoes, seafood, and extra virgin olive oil) has been linked to a better mood — something that, perhaps, is brought about by changes in the gut microbiome.
Bottom line? We’re not yet at the point where scientists can specifically indicate a cocktail of probiotic organisms for specific mental health conditions. But if you do want to improve your general gut health, Perlmutter notes that probiotic foods — kimchi, sauerkraut, yogurt, and kefir — have been shown to reduce inflammation, while prebiotics — garlic, onions, leeks, chicory root, dandelion greens, Jerusalem artichoke, and jicama — can also nurture good gut bacteria.
