The Surprising Gut-Brain Connection

Stephanie Wells, MS, RD, LD

The topic of mental health hasn’t always been openly discussed or researched as much as it deserves, but thankfully that fact is changing. The ability to manage our thoughts and emotions in a healthy, productive way is crucial for reducing stress and maintaining healthy relationships with family and friends. It also plays a significant role in our ability to contribute to society through our careers, volunteering, and keeping up our physical health. 

It’s estimated that 15–20 percent of people will develop a mental health disorder, such as depression or anxiety. These are both among the top 10 worldwide causes of losing healthy, disease-free years from our lives. Since so many people are affected, it’s important to know if depressive disorders are inevitable or whether there’s anything we can do to reduce our risk.

Fortunately, there is something we have the power to change within our own bodies that can help reduce the risk of some mental health disorders: our gut bacteria. Also known as our gut microbiome, the bacteria in our intestines play a fascinating and surprising role in supporting our mental health. Let’s take a closer look.

What Is the Gut Microbiome?

You may know that our bodies are naturally covered in bacteria, but did you know that the majority of this bacteria is located in our gut? It’s true—there’s an incredible two to six pounds of bacteria in your intestines, comprising about 160 different strains of bacteria. This includes both harmful and helpful bacteria. In healthy people, the amount of beneficial bacteria typically outweigh the amount of harmful bacteria.

However, we know that the risk of developing many different chronic diseases increases when we have too much harmful bacteria and not enough helpful bacteria. This is true for common health conditions such as type 2 diabetes, metabolic syndrome, irritable bowel syndrome, and some types of cancer. We’ve known this for a while, but science is just starting to uncover how our gut bacteria influence mental health disorders as well.

The Hidden Conversations Between the Gut and Brain 

So how are these gut bacteria related to our mental health? In a nutshell, the gut microbiome and the brain communicate with each other in a relationship that scientists call the microbiome-gut-brain-axis. This relationship goes both ways, with the brain impacting the gut microbiome and the gut microbiome impacting the brain. Researchers believe that this relationship plays an important role in brain function and health.

This can happen in different ways. For one, about 95 percent of the body’s total serotonin is produced in the gut by the bacteria that live there. Serotonin is a neurotransmitter responsible for feelings of happiness and calmness. Low levels of serotonin are seen in people with depression. These helpful bacteria also produce other chemicals important for the brain and central nervous system, such as dopamine, norepinephrine, and acetylcholine.

Changes in the types and amounts of bacteria present in the gut have been seen in cases of depression, anxiety, schizophrenia, and bipolar disorder. It isn’t always clear which comes first—whether a poor balance of gut bacteria contributes to the development of these conditions, or whether these conditions lead to habits that negatively impact the gut. Either is possible and may vary based on the individual.

In what other ways can an unhealthy gut microbiome increase the risk of mental health issues? Another explanation is inflammation. When harmful bacteria outnumber good bacteria, chronic inflammation develops in the gut. Inflammation can increase the risk of some mental health disorders by weakening the protective lining of the gut and allowing for the intrusion of harmful bacteria. It can also reduce the amount of serotonin produced in the gut. Inflammation can also occur when there aren’t enough beneficial bacteria to produce vitamin K2 and certain B vitamins.

When You Feel Poorly, You Eat Poorly. 

While a nutrient-poor diet can increase the risk of certain mental health conditions, the reverse can be true as well. Anyone who has suffered from mental health issues can tell you that when your head isn’t in a good place, you’re less likely to have the mental and emotional bandwidth to focus on eating a healthy diet. Some people may not be able to eat much at all if they’re suffering from a poor appetite, which can lead to malnutrition if not addressed quickly.  

Depression and stress can even change your perception of how foods taste, making sweet flavors and high-fat foods more enticing. This can make it even more challenging to maintain a balanced diet when you’re struggling. 

Healing Your Gut 

Mental health is a complex topic, and gut health is far from being the only factor that plays a role in mental health disorders. However, we have the powerful ability to support the growth of beneficial, anti-inflammatory bacteria in our intestines by eating a nutrient-dense diet rich in fruits, vegetables, healthy fats, and plant-based protein and low in added sugars, saturated fat, fried foods, and animal products. Taking a probiotic can help as well. 

These gut-friendly foods can help manage stress and reduce the risk of developing mental health disorders, such as depression and anxiety. This type of eating pattern is consistent with widely accepted nutrition guidelines and is a great strategy for anyone looking for ways to support their mental health.

Stephanie Wells, MS, RD, LD, is a registered dietitian working in cancer research. She has a passion for plant-based nutrition and has been published in numerous scientific journals.

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