Can your microbiome affect your mood? Experts weigh in on surprising gut-brain connection at play.

By Julia Malacoff and Pamela O'Brien
Updated December 02, 2020
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Credit: Getty Images Design: Alex Sandoval

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.

Here, top experts in the field explain the gut-brain connection, or 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 Connection?

"The gut-brain axis 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 gut-brain axis 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 gut-brain axis 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. (Related: How to Improve Your Gut Health — and Why It Matters, According to a Gastroenterologist)

There are two primary ways the stomach communicates with the brain (that are currently known). "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," says Kelly. "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," says Kelly. 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 The Gut-Brain Connection 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," says Talbott, 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 connection 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," says Talbott.

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 for Your Gut-Brain Connection

How can you know if mental health problems are linked to your gut health? 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 for your gut-brain connection, experts agree, is prioritize healthy eating to promote a healthy microbiome. "The more balanced [your diet] is, the more likely you are to have the right mix of healthy microbes in your gut,” says Vanessa Sperandio, Ph.D., a professor of microbiology and biochemistry at the University of Texas Southwestern Medical Center. That, in turn, helps your gut produce enough serotonin to make you feel happy — and keep you healthy.

After all, the impact that food makes on your body and brain is so powerful that “what you eat affects your gut bacteria within 24 hours, and the composition of your microbiome starts to change,” says Uma Naidoo, M.D., the author of This is Your Brain on Food and the director of the Nutritional & Lifestyle Psychiatry Clinic at Massachusetts General Hospital. “Because your gut is directly connected to your brain through the vagus nerve, your moods can be affected as well.” Here’s how to eat in order to keep your outlook bright and your GI system strong. (Related: Is the Microbiome Diet the Best Way to Promote Gut Health?)

Keep a food diary.

"A good long-term approach is to learn to listen to your body," says Kelly. "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.

When you consume foods rich in fiber, your body has to break them down. “Doing that work helps keep your gut microbes healthy,” says Sperandio. “But if you eat processed foods, those have already been broken down for you. The makeup of your microbiome changes in response, and that’s when you start to have metabolic issues like high blood pressure and high blood sugar.”

It's also 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, adds Talbott. "It's the number-one way to improve microbiome balance," he says. To keep your gut bugs happy, avoid too much packaged stuff, and load up on vegetables and fruits daily, plus whole grains like oats and farro. (Related: 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.

Add key spices to your diet.

To boost your mood when you’re feeling low, Dr. Naidoo recommends having some turmeric with a pinch of black pepper. “Several controlled trials have shown that this combination improves depression,” she says. A substance in black pepper called piperine helps your body absorb curcumin, an antioxidant in the turmeric. So whip up a golden latte with turmeric and some black pepper. Or add the ingredients to plain Greek yogurt for a dip for veggies. That gives you the probiotic benefits of the yogurt, which help replenish your good gut bacteria.

Eat away at stress.

During trying times like these, we’re likely to feel anxious, which sets off a chain reaction in our bodies. “Chronic stress negatively affects your gut bugs, and your microbiome gets thrown off-balance,” says Dr. Naidoo. “Bad gut bugs start to take over, and that causes inflammation, which affects your mental health.” Her prescription? “Eat foods rich in anti-inflammatory and mood-boosting omega-3 fatty acids, like salmon.”

Do your ABCs.

Eating foods high in vitamins A, B, and C can help fight anxiety and will improve your mood, according to Dr. Naidoo. For vitamin A, reach for mackerel, lean beef, and goat cheese. Get your Bs from leafy greens, legumes, and shellfish. And broccoli, Brussels sprouts, and red and yellow peppers will give you plenty of C.

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