How Gut Bacteria Impact our Brain and Mental Health


Often, we think of bacteria as the culprits of infections and illnesses – something to eliminate from our environment. 

While it is true that some types of bacteria, viruses, and fungi can cause illness, and are even deadly, there are thousands of species of microorganisms that not only support the proper functioning of bodily systems but are vital to our health and wellbeing. These are the good bugs. 

The population of good bugs in our gut are referred to as the gut microbiome. Discussions and research around the gut microbiome are often focused on digestive health and nutrition. While this is a vital role of the gut microbiome for our overall health and wellbeing, there is another role of gut bacteria in our overall health that is often overlooked; the status of an individual’s gut microbiome has a profound impact on mental health. 

How do gut bacteria impact our mental and emotional health? Read on to learn about the science and mechanisms for how good bugs affect your brain. 

 

What is the Gut Microbiome? A Refresher

The gut microbiome is the term for the collective population of bacteria, viruses, and fungi that live in the gut. A normal gut microbiome doesn’t include pathogenic bacteria, viruses, and fungi – of those that cause infection and illness. They are either benign or functional for our body’s digestive, regulatory, and immune processes. 

Normal gut microbiome imparts specific functions in the body, including: 

  • nutrient metabolism
  • xenobiotic and drug metabolism
  • maintenance of structural integrity of the gut mucosal barrier
  • Immunomodulation
  • protection against pathogens

An individual’s gut microbiome at any given time is the result of numerous historic, environmental, and internal or biological factors, including:

  • Method of delivery at birth: A person born by vaginal delivery is exposed to more benign bacteria, which influences the gut microbiome. 
  • Infant feeding method: Children fed by breastfeeding are more likely to have a more diverse microbiome. 
  • Genetic makeup: A person’s genetics affect human metabolism and the number of specific bacteria found in the gut microbiota.
  • Infections, past and current: Pathogenic infections can displace or kill bacteria that promote health. 
  • Medications: Antibiotics can kill beneficial microbiota in addition to the pathogenic microbiota. Other medications can affect metabolism and overall conditions in the body that support beneficial bacteria. 
  • Supplementation: supplementation with probiotics and specific vitamins may impact the gut microbiome
  • Diet: overall nutrient intake and dietary patterns affect the diversity and population of gut bacteria. We discuss the specific dietary factors that affect gut microbiota in a later section. 
  • Exercise: Moderate, regular exercise and physical activity reduces inflammation and helps to create an environment where beneficial bacteria can thrive. 
  • Stress: Chronic stress or extreme distress can cause irregularities in the immune system which make it easier for pathogenic bacteria to colonize the gut. Additionally, stress can modify behaviors and lifestyles that are not supportive of overall health and wellness. 

The Gut-Brain Axis: How the Gut Microbiome Affects Mental Health 

The field of Nutritional Psychology has uncovered the multiple ways in which certain nutrients and eating patterns can affect mental health. Because of the work and research of nutritional psychologists, we do not know how what we eat may affect brain function and, ultimately, our mood. For example, research suggests that improvements in dietary diversity and quality lower the risk of depression and the appearance of anxiety. Because depression is an inflammatory condition, an anti-inflammatory diet might contribute greatly to treatment.

How does what we eat affect our mood and overall mental health? 

One of the paths in which the gut microbiome can affect mental health is via the gut-brain axis, which is “bidirectional interactions between the central nervous system, the enteric nervous system, and the gastrointestinal tract.”. The study of the gut-brain axis has revealed that there is a vast system of communication between two bodily systems that many people view as separate. In fact, these systems are closely intertwined, as we describe below.

The gut-brain axis is made up of: 

  • The central nervous system. It includes the brain and the spinal cord, and the enteric nervous system includes the neural circuits that control basic functions like blood flow, secretions, mucosal transport, and the modulation of immune and endocrine functions. 
  • The gastrointestinal tract, or GI tract. This is the series of hollow organs that include the mouth, esophagus, stomach, large intestine, small intestine, and anus. 
  • Other organs that are part of the digestive system and have direct interaction with the GI tract: they include the liver, the pancreas, and the gallbladder. 
  • The gut microbiota: the population of bacteria in the gut. 

For more information on this, check out the article on how the gut-brain axis impacts mental health. 

Good Bugs in the Gut: The Link Between Digestive and Mental Health?

While the bacteria in the intestines has traditionally been encompassed in the gut side of the gut-brain axis, the microbiota are completely separate microorganisms to the host (us, the humans!).

Not only diet but measurable alterations in gut microbiota have been associated with mood and depressive disorders. In fact, a diverse and populous variety of species of gut microbiota can help to maintain normal mental processes just as it is involved in mental and neurological diseases. 

What does gut bacteria have to do with mental health? Our emotional and mental state has an impact on the chemicals that circulate in the body, which can create an environment that either welcomes or shuns off microorganisms. 

Let’s look at an example. Mental health conditions and disorders affect the synthesis of several chemicals, including hormones like cortisol. Cortisol activates molecular patterns associated with danger, and chronically activates stress cascades. These, in turn, modify the production of a number of circulating stem cells, creating an unwelcome environment for friendly bacteria. This results in dysbiosis, or a lack of balance in intestinal microbiota.

At the same time, gastrointestinal diseases that cause dysbiosis, affect the production of short-chain fatty acids, neurotransmitter synthesis, and chemical signaling. These also affect the production and modulation of circulating stem cells, which cause a chemical imbalance in the brain. 

Food and Mood: Diet Quality and Its Effect on Gut Microbiome ad Mental Health

The connection between gut microbiota and brain health is clear. So, establishing a balance of good bugs gut can improve some of the factors that influence mental health. 

How can we establish a healthy population of microbiota in the gut? One of the ways is through diet.

Diet quality can affect the gut microbiome by reducing or limiting the diversity of beneficial microorganisms in the gut. What a person eats can lead to infection by pathogens, inflammation, and the erosion of the mucus layer in the intestine. This may lead to intestinal permeability and low short-chain fatty acid levels. 

A diet that is not supportive of a healthy gut is predominant in the following foods: 

  • Meat and processed meats
  • Foods rich in probiotic bacteria
  • Saturated fats
  • Refined grains
  • Sugar
  • Salt
  • Alcohol
  • Corn-derived fructose

On the other hand, a diet predominant in the following foods support gut health:

  • Fruits
  • Vegetables
  • Fiber
  • Plant-derives proteins 
  • Monounsaturated fatty acids
  • Omega-3 polyunsaturated fatty acids

Read this diet to learn about foods that help support gut health

Main Takeaways

The role of nutrition and eating habits can affect mental health in many ways. One of the ways is through the impact of what we eat on the gut microbiome. Remember, however, that nutrition is only one factor that affects the gut microbiome and overall mental health and wellness. There are many factors that influence mental health, including:

  • Genetic factors
  • Other conditions and diseases, past and present
  • Medications
  • Supplements
  • Social determinants of health and wellness include life experience, discrimination, and trauma. These have the biggest influence on mental health

Exploring the nuances and complex connections between habits, environment, genetics, microbiota, biology, and personal health history can seem confusing at times, but it is helpful for having greater sensibilities for the multidimensional ways in which health is produced and maintained by that over which we have control, and that which we do not. 

 

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References

  1. https://www.sciencedirect.com/science/article/pii/S0399077X13003077
  2. https://www.sciencedirect.com/science/article/pii/B9780128130377000042
  3. https://www.researchgate.net/publication/304070457_The_role_of_Gut_Microbiota_in_the_development_of_obesity_and_Diabetes/figures?lo=1
  4. https://www.sciencedirect.com/science/article/pii/S0271531721000580
  5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5483960/
  6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6699480/
  7. https://www.frontiersin.org/articles/10.3389/fnut.2021.644138/full
  8. https://www.frontiersin.org/articles/10.3389/fnint.2018.00033/full
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  11. https://www.sciencedirect.com/science/article/pii/S0278584610002319
  12. https://www.jci.org/articles/view/76304 





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