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The gut-brain axis: How your gut affects your mental health

It's not all in your head. The bacteria in your gut have a distinct effect on your brain and mental health, researchers say.

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It's no longer news that the state of mental health in the US is dire. Between an ongoing pandemic, a tumultuous election year and so much worldwide unrest, even someone with the most solid mental health state could struggle in recent times.

Mental health is very complex, and no one thing can change it alone. Experts say a mix of factors -- including genetics, lifestyle, environment and emotional factors -- influence mental health outcomes. But something that science has begun to understand more than ever is that mental health is not solely, well, mental. 

Research is increasingly showing that gut health, largely the gut microbiome (or the community of bacteria that live in your gut), plays a huge role in the intricate puzzle that is mental health. In fact, your gut and brain are intimately connected to one another and in constant communication through something called the "gut-brain axis." By understanding this connection, you can work on improving your own mental health in entirely new ways.

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What is the gut-brain axis?

Scientists have discovered that the gut and the brain influence each other through what is known as the gut-brain axis. Essentially, this is the route that your gut and nervous system use to send signals to one another. From this connection, researchers have been able to link gut issues (like dysbiosis -- when good bacteria is low) and inflammation in the gut to mental health disorders. 

"All the original work came from studies in mouse models which showed that manipulations of the mouse microbiome could alter emotion-like behavior in these laboratory animals," says Emeran Mayer, MD and author of The Mind-Gut Connection

What makes for a healthy gut microbiome?

One of the biggest influences on gut health is the food that you eat on a daily basis, which can alter your gut microbiome and send changes along the gut-brain axis. "Several molecules generated by gut microbes from the food we eat can reach the brain via the circulation," Mayer explains. They can also "activate receptors on vagal nerve endings, which in turn generate vagal signals to the brain," he says.

The good news is that if you're not currently eating for a healthy gut microbiome, it's not too late to change your diet, and therefore change your gut bacteria. 

"Amongst several lifestyle factors (sleep, exercise, diet, mental factors), diet has a prominent role in determining gut health," Mayer says. "A healthy, largely plant-based diet, made up of a variety of different fruits and vegetables, nuts, seeds and naturally fermented food is generally associated with a healthy gut. A diet deficient in these ingredients, but high in ultra-processed foods, refined sugar and animal fats, such as the Standard American Diet (SAD) is one of the main reasons for… poor gut health."

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Neurotransmitters that play a role in mental and brain health are produced in the gut.

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Neurotransmitters are influenced by gut bacteria

The bacteria in your gut are also responsible for producing many of the neurotransmitters that play key roles in your brain, and overall mood and mental health. Serotonin, which is known as the "happy" chemical or hormone, is largely produced in the gut. Researchers estimate that about 90% of all of your serotonin is made in the gut. One of the ways this happens is via bacteria that send signals to the gut to make serotonin. 

Other neurotransmitters that play a role in mood and mental health are dopamine, GABA and norepinephrine, all of which are also produced in the gut. There is still a need for more research on these connections to fully understand how they work.

The gut-based immune system

According to Mayer, another major way that your gut is linked to your brain is through the immune system, a large part of which is actually based in the gut. This gut-based immune system is capable of triggering "a systemic immune activation" throughout other parts of your body, Mayer says -- "which can induce activation of glial cells in the brain, leading to neuroinflammation and neurodegeneration." Inflammation and degeneration are two key concerns when it comes to overall brain health and mental health. 

Research on how exactly the gut-based immune system works and may affect health care moving forward is still ongoing. "Many human studies are underway aiming to establish a causative role of the gut microbiome on human brain alterations and behavior, " Mayer says. He noted that this research could be particularly important for understanding Parkinson's and Alzheimer's disease further, but could also help us understand other conditions, including major depressive disorder.

One thing is certain: your diet makes a difference in your gut health, and therefore your brain health. "For all these brain disorders, there is evidence from large scale epidemiological studies that consumption of a largely plant-based diet is associated with a lower prevalence of disease," he adds.

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The gut microbiome is only one piece of gut health

As much focus as there is on the gut microbiome, it's important to realize that the microbiome is not the only factor in gut health. Other things to consider include gut permeability and overall gut functioning. A less permeable, tight intestinal barrier is what prevents what's often known as "leaky gut," or when the bacteria that is meant to stay in the gut "leaks" to other areas. It also "prevents direct contact between microbes and the gut based immune system, preventing immune activation," Mayer says. 

In addition, a healthy gut means that other gut-based functions, including the processes that regulate appetite, digestion and elimination, are all healthy and working well.

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The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.