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The Surprising Way Your Brain and Gut Are Connected

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These days, it feels like everyone and their mom takes probiotics for digestive and overall health. What once seemed like a potentially helpful but maybe unnecessary supplement has become a widespread recommendation among mainstream and integrative health experts alike. There are even probiotic skin-care products—and (spoiler alert!) dermatologists say they're worth using. Even crazier, scientists are beginning to learn that the bacteria in your gut not only affects your day-to-day life through digestion, but also how you feel mentally on an everyday basis. We tapped top experts in the field to find out how your gut affects your brain, how advanced the science is in proving their link, and what you can actually do about it.

What Is the Gut-Brain Axis?

"The gut-brain axis (GBA) refers to the close link and constant communication between our 'two brains': the one that everyone knows about in our head, and the one that we've just recently discovered in our gut," explains Shawn Talbott, Ph.D., a nutritional biochemist. Essentially, the GBA is what links the central nervous system (the brain and spinal cord) with our "second brain," which consists of the dense, complex network of nerves around the gastrointestinal tract, known as the enteric nervous system, along with the bacteria living in our GI tract, which is also known as the microbiome.

"The microbiome/ENS/gut communicates with the brain through the 'axis,' sending signals through a coordinated network of nerves, neurotransmitters, hormones, and immune system cells," Talbott explains. In other words, there's a two-way street between your gut and your brain, and the GBA is how they communicate.

"We used to think messages were sent mainly from the brain to the rest of the body," says Rachel Kelly, coauthor of The Happiness Diet. "Now, we're realizing the stomach also sends messages to the brain." This is why nutrition is emerging as an important factor in mental health, as it's the primary way to impact your gut's microbiome.

There are two primary ways the stomach communicates with the brain (that we know of!). "There are eight neurotransmitters that affect happiness, including serotonin and dopamine, sleep-inducing melatonin, and oxytocin, which is sometimes referred to as the love hormone," Kelly says. "In fact, as much as 90 percent of serotonin is made in our gut and around 50 percent of dopamine." These neurotransmitters partially determine how you feel on a daily basis, so it stands to reason that when the microbiome is out of balance and the neurotransmitters aren't being produced effectively, your mental health could suffer.

Second, there is the vagus nerve, which is sometimes referred to as a "phone line" connecting the brain and gut. It runs on each side of the body from the brain stem through the chest and abdomen. "It makes sense that the brain controls a lot of what the gut does, but the gut itself can also impact the brain, so the communication is bidirectional," Kelly says. Vagus nerve stimulation is sometimes used to treat epilepsy and hard-to-treat depression, so its connection to and impact on the brain is well-established.

Is This Legit?

We know that there's definitely a connection between the brain and the gut. How exactly that connection works is still somewhat of a working theory. "There isn't really any debate at this point about the existence of a gut-brain axis," Talbott says, although he does point out that many physicians didn't learn about it in school because it's a relatively recent scientific development.

According to Talbott, there are still some important things about the gut-brain axis that scientists are trying to figure out. First, they're not sure how to measure a "good" vs. "bad" gut microbiome status or how exactly to reestablish balance. "At this point, we think that microbiomes might be as individual as fingerprints, but there are some consistent patterns associated with a 'good' versus a 'bad' balance," he says.

There are plenty of studies showing the connection between brain-related conditions and certain gut microbes, but the links are not that clearly defined at the moment. "There's evidence supporting microbiata-gut-brain interactions and how the disruption of this communication is found in patients with anxiety, depression, ADHD, autism, and dementia just to mention a few," says Cecilia Lacayo, M.D., a board-certified integrative physician. It's important to note, though, that the bulk of this research has been done in mice, which means that human studies are needed before conclusions can be more concretely drawn. Still, there's incredibly little doubt that gut microbiomes are *different* in people with these conditions.

Secondly, they're still figuring out which strains of bacteria (aka pre- and probiotics) are most helpful for which issues. "We know that the benefits of probiotics are very 'strain dependent.' Some strains are good for depression (like lactobacillus helveticus R0052); some are good for anxiety (like bifidobacterium longum R0175); and some are good for stress (like lactobacillus rhamnosus R0011), while still others are good for constipation or diarrhea or immune support or reducing inflammation or cholesterol or gas," Talbott says.

In other words, simply taking probiotics, in general, isn't likely to be that helpful for mental health. Instead, you'd need to take a targeted one, which your doctor may be able to help you select if they're up on the most recent research.

What You Can Do

How can you know if mental health problems are linked to your gut? The truth is, you can't really—yet. "There are tests for this, but they're expensive and only give you a snapshot of your microbiome at that moment," Kelly explains. Since your microbiome changes, the information these tests provide is limited. The best thing you can do, experts agree, is to prioritize healthy eating to promote a healthy microbiome. Here are their top suggestions:

Keep a food diary: "A good long-term approach is to learn to listen to your body," Kelly says. "Become your own detective by keeping a food diary for a start to notice how certain foods impact on your mood," she says.

Eat more fiber: "It's the number-one way to improve microbiome balance," Talbott says. It's thought that fiber from fruits, vegetables, beans, and whole grains helps to "feed" the good bacteria and "starve" the bad bacteria, meaning you could get more of the "happy/motivated" signals and fewer of the "inflamed/depressed" signals being sent between your gut and brain, Talbott says. (More: These Benefits of Fiber Make It the Most Important Nutrient In Your Diet)

Focus on whole foods: Advice for eating to improve your mental health is pretty similar to general healthy eating advice. "Lifestyle choices are the first change that you can make now to improve the health of your microbiome," says Dr. Lacayo. Foods with a positive impact on the gut-brain connection include seeds, raw nuts, avocado, fruits and vegetables, and lean animal protein, she says. Dr. Lacayo also recommends cooking with healthy fats like coconut oil, avocado oil, and organic ghee.

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