How Does the Gut Microbiome Affect Mental Health?

KOTRYNA ZUKAUSKAITE

Thankfully, we’ve come a long way from the idea that mental health issues are “all in your head.” In fact, there’s a growing body of evidence that what’s happening in your digestive system can play a big role in your mood and emotional state—and vice versa. And those so-called gut feelings or instincts? They’re pretty damn real too.

“The gut is the most complex organ, secondary only to the brain,” says Emeran Mayer, MD, a gastroenterologist and neuroscientist. It is filled with millions of nerves as well as large portions of your immune and hormone systems, he says, all working hard to transform the food you eat into the nutrients you need to thrive. To stay in sync, your gut chats with your brain 24/7 via a complex network called the “gut-brain axis”—and it’s this network that can potentially shape your mental and physical health.

The gut’s relationship to mental health is a newer field of study. And full disclosure: There is a lot we still don’t know about how the gut and the brain work together. Many recent studies are preliminary or based only on cell or mice experiments. But what we do know is illuminating—and has implications for how we’ll address mental health in the near future. To learn more, we talked to top experts in this field about how much our emotions are influenced by our guts.

Table of Contents

Inside the Mind-Gut Connection

As mentioned earlier, your gut and brain are constantly talking to each other like teens in a group chat. How this communication works is complicated, but emerging research suggests that your gut microbiome—the vast community of bacteria and other microbes in your digestive system—likely plays a significant role. These bugs chow down on your undigested food scraps (pizza, grain bowls, and everything in between) to make various kinds of metabolites—science-speak for food by-products. These metabolites trigger different responses from your brain and body, says Mayer.

For example, say you’re eating a kale salad or veggie sandwich for lunch. Your gut microbiota “eat” it too, producing short-chain fatty acids in the process. Some research suggests that these acids may prompt your endocrine system to make the hormone leptin, which tells your brain that you’re full.

Between 90 and 95 percent of our serotonin is in the gut.

Your microbiome also makes neurotransmitters, a type of chemical messenger that carries signals between your nervous system and the rest of the body. Chief among these is the “happiness hormone” serotonin. “Between 90 and 95 percent of our serotonin is in the gut, and a lot of serotonin is made in the gut,” says Uma Naidoo, MD, a nutritional psychiatrist and nutrition specialist and the author of Calm Your Mind with Food. In your brain, serotonin hugely influences your mood and sleep habits. Elsewhere in your body, it’s used to help regulate appetite and gut function. Research suggests that changes to your gut microbiome can impact your body’s balance of serotonin and other neurotransmitters, which can potentially mess with your mood.

Having a ‘Gut Feeling’

Having a healthy, “happy” gut—full of good bugs working overtime to relieve inflammation and make good-for-you metabolites—typically correlates with a positive mood, less stress, and a sharper mind, says Naidoo. But the gut-brain relationship is complex, says Lin Chang, MD, a gastroenterologist specializing in disorders of the gut-brain interactions. Sometimes life (or illness, or stress) comes along to disrupt the balance, which may have implications for your health.

For example, eating tons of ultra-processed foods on the reg can cause inflammation, says Naidoo. Inflammation harms the good bugs in your gut and promotes the growth of “bad” ones, which might affect your mental health. In fact, a 2021 review found that people with various psychiatric disorders (including depression and anxiety) tend to have greater numbers of pro-inflammatory bugs than anti-inflammatory ones in their microbiomes. (On the flip side, people who are more resilient to stress tend to have lots of anti-inflammatory gut microbes.)

“A chronically unhealthy diet and chronic abnormal signaling from the gut to the brain can have major negative effects, like inflammation in the brain,” adds Mayer. Brain inflammation is associated with depression as well as an increased risk of neurodegenerative diseases like Parkinson’s and Alzheimer’s.

Chang says that regularly experiencing digestive problems—or even a bout with severe food poisoning—can also change the microbial balance of the gut and throw a wrench in your mental health. Conversely, she says, surviving trauma or prolonged levels of stress can lead to gastrointestinal problems.

Irritable bowel syndrome (IBS)—a disorder that causes symptoms like chronic stomach pain, diarrhea, or constipation—is one of the clearest examples we have of the gut-brain connection at work. With IBS, there’s nothing physically amiss that would explain your symptoms, says Chang. Instead, experts believe something happens to throw your gut-brain communication out of whack. We don’t definitively know what triggers that imbalance. But interestingly, IBS often pops up in people who have depression, anxiety, and other mental health conditions.

“Mental health doesn’t just begin from the neck above,” Naidoo says. “It’s really the whole body and also in the gut microbiome.”

How to Have a Happy Gut

It bears repeating that we’re in the early stages of understanding the microbiome. We’re not at the point yet where we can, say, prescribe a probiotic for depression, says Chang. But all evidence suggests that what happens in your digestive tract is reflective of (or can predict) what’s going on in your brain. And the food you eat has a major impact on your gut, says Naidoo.

To support a happy gut, all three doctors recommend eating a balanced, nutrient-rich diet while avoiding or limiting inflammatory, ultra-processed eats. (Mayer is specifically a fan of a Mediterranean-style diet.) Doing so will support an abundance of good bacteria and decrease inflammation, says Naidoo, and it’s associated with a reduced risk of depression. Talk about a win-win.

Mental health doesn’t just begin from the neck above. It’s really the whole body.

Fiber is also crucial. If you’ve been skimping on vegetables, Naidoo recommends gradually increasing serving sizes to work up to the recommended 25 grams of fiber a day. This slow-and-steady approach lets your digestive system gradually adjust while avoiding annoying symptoms like gas, bloating, constipation, or diarrhea.

Chang adds that fermented foods (like yogurt and kimchi) are also essential because they throw more beneficial bacteria into the mix. She also suggests eating foods loaded with the amino acid tryptophan, which your body uses to make serotonin. Options include tuna, oats, bananas, chicken, turkey, prunes, and peanuts.

Of course, mental health is bigger than what you eat. “Just focusing on your diet and not changing your lifestyle misses the boat,” says Mayer. Finding healthy ways to manage stress, prioritizing self-care, going to therapy (if it’s helpful for you), and taking prescription medications (if needed) can all support both your mental health and your gut health—right alongside a nutritious diet.

link