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The Emerging Science of Gut Feelings

Learn about how your brain, your gut, and its microbiota work together to impact your emotional balance, moods, and behaviors.

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Contributing Writer

You’ve probably felt “butterflies” before a big presentation or a tight knot forming in your stomach after receiving really bad news.

Recently, science has begun to unravel the fascinating biological explanations for why those “gut feelings” happen, with a growing body of research that shows the close relationship between our digestive system and brain, and how communication between the two can impact everything from emotions and moods to decision making and behavior.

“The intense information exchange between your brain, your gut, and its microbiota takes place 24 hours a day, regardless if you sleep or are awake, from the day you are born to the day you die,” writes renowned gastroenterologist, neuroscientist, and UCLA professor Emeran Mayer, M.D., Ph.D., in his new book The Mind-Gut Connection. “And if we listen carefully, this conversation can also guide us toward optimal health.”

Gut health has been a trending health topic for the past few years, as knowledge of how profoundly the microbiome—the trillions of microbes that live in your gut and elsewhere in the body—affects individual health has grown. But most research has focused on how microbes affect the immune system, and therefore inflammation and chronic disease risk.

Related: The Hidden Health Factor Everyone is Talking About

How these microbes interact with the body’s nervous systems is less established, but that’s quickly changing. “It’s a field in rapid evolution,” Mayer says, and it’s worth paying attention to if you want to live well. Here’s why.

Your “Second Brain” and Its Microbe Mediators

You’ve likely heard of the Central Nervous System (CNS), made up of the brain and spinal cord, and the Peripheral Nervous System (PNS), which consists of the nerves in the rest of the body that transmit signals to and from the CNS to other parts of the body, like muscles and organs.

But there’s another network, the Enteric Nervous System (ENS), and its millions of nerve cells are embedded in the lining of the gastrointestinal tract from the esophagus all the way to the rectum, Mayer explains. It’s so vast and complex that researchers often refer to it as the “second brain” or “little brain.”

And while the ENS’ main job is to regulate digestion, which it does almost entirely without the help of the brain, it also transmits regular signals to the brain via the vagus nerve.

What kinds of signals is it relaying and where does the microbiome come in? “The microbes sit on this crucial interface between the signals that go up to the brain and signals that come back from the brain,” says Mayer, and studies have shown they likely play a crucial role in relaying information back and forth. “There’s quite a bit of science, mainly from mouse studies in the last five to ten years, that has established this concept that if you alter the gut microbial composition, you can observe changes in mouse behavior… and all of these behaviors are presumed examples or correlates of human’s complex behavioral traits.”

Emotional Impact

Here are some examples of how that may work.

Research has shown some gut microbes are able to produce the neurotransmitter GABA, a signaling molecule that keeps the emotional part of the brain regulated. (Popular anti-anxiety medications like Valium and Xanax mimic the molecule.) Therefore, how much is being produced in your gut and transmitted to the brain via the vagus nerve could impact anxiety levels. In fact, studies have suggested that in normal mice, “gut microbes produced a steady supply of substances that were able to suppress anxiety, and their effect was transmitted to the brain through the vagus nerve,” Mayer writes.

95 percent of the body’s serotonin—a signaling molecule that plays a major role in regulating sleep, appetite, and mood—is also stored in the gut. “Microbes produce signaling molecules that can directly communicate with serotonin-producing cells,” Mayer says. “60 percent of the production of serotonin in those cells is dependent on the microbes.” So if your microbes are out of whack, it may affect how much serotonin is reaching your brain, and therefore those many systems that depend on it.

How to Optimize Mind-Gut Communication

A healthy gut is generally defined as one that is home to a diverse, stable, resilient community of microbes, but unfortunately, most of those microbes establish residency early in life, finding their way into your system via pathways like the birth canal and breastfeeding. “The biggest programming of the system clearly happens in the first three years, including pregnancy,” Mayer explains, so while it may be difficult to completely change your microbiome’s composition, researchers think that via diet and lifestyle, you can essentially alter the metabolites the microbes produce, and therefore the signals they send out. “It’s like an orchestra that gets assembled, with all the different players and instruments, and what it plays later in life has a lot to do with the inputs it gets from the conductor.”

His advice? First and foremost, maximize plant-based foods in your diet, since they contain prebiotic fiber that nourishes microbes, and minimize animal fat. Avoid processed foods to steer clear of additives like artificial sweeteners and emulsifiers, which can disrupt the protective lining of the GI tract, and go organic when you can. Eating fermented foods like sauerkraut, kimchi, miso, and yogurt regularly may also be beneficial.

Related: How to Really, Really Listen

Finally, think about how your mental state relates to your meals, Mayer says, and don’t sit down to eat when you’re stressed, angry, or sad, as your gut will already be in an unbalanced state. On the flipside, enjoying meals with people you love is probably good for your microbes.

“The resulting sense of connectedness and well-being almost certainly affects the gut and influences how your gut microbiota respond to what you eat,” he writes. That’s right, science just gave you a reason to host more dinner parties with friends.



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