Mental health is not relegated to the brain. In fact, the digestive tract - especially the colon - play a key role in the production and reception of neurotransmitters, which is one of the reasons the gut has been called our 2nd brain. More specifically, the "2nd brain" is the ecosystem of microorganisms (the microbiota) taking up residency in the colon. To learn more about the microbiota, read Dr. Barrett's blog titled Microbiome and my previously published blog, This is Your Microbiota on Stress.

One way that the microbiome communicates with the brain is by stimulating the vagus nerve. The vagus nerve travels down the brain stem into the spinal column, innervates the abdomen and then spreads out to create a web-like cage for the digestive tract. Microbes in the colon ”tickle” the vagus nerve to communicate directly with the brain, stimulating production and secretion of neurotransmitters that contribute directly to mental wellness, including serotonin, dopamine and others. Additionally, the microbiota play a significant role in what kind of signaling molecules are produced in the gut that then communicate with the brain.

The microbiota also impacts a part of the brain called the amygdala. The amygdala "...is commonly thought to form the core of a neural system for processing fearful and threatening stimuli, including detection of threat and activation of appropriate fear-related behaviors in response to threatening or dangerous stimuli."  The composition of the microbiota - both the overall population and the diversity of the ecosystem -  impacts how the amygdala develops a response to stressful stimuli and the extent to which anxiety manifests in an individual. In this way, microbiota modification via diet, lifestyle and therapeutic probiotic supplements holds promise for mental health. 

Another way in which the health of the microbiota contributes to the health of the mind/heart is via  maintenance of the structural integrity of the digestive tract.

In addition to beneficial microbes like species of lactobacillus and bifidobacteria, we also host strains of streptococcus and staphylococcus, candida and other yeasts. These potentially pathogenic microbes make toxic compounds called lipopolysaccharides (aka endotoxins). Lipopolysaccharides (LPS) dismantle the harmony not just in the colon but in the small intestine too. When the microbiota is imbalanced and the potentially pathogenic microbes gain a stronghold, over time the accumulation of LPS in the digestive tract can cause intestinal permeability or "leaky gut syndrome." In a leaky gut, the barrier of the small intestine is inflamed and compromised to the extent that nutrients are not absorbed and larger molecules escape the digestive tract intact, causing inflammation throughout the body. 

With leaky gut we are posed with two factors contributing to mental wellness:

1. Micronutrients, amino acids, fatty acids and minerals needed for the production, secretion and reception of neurotransmitters may not be digested and absorbed sufficiently. Overtime, this can lead to nutritional insufficiencies and compromise mental health on a biochemical level.
2. When unchecked over a prolonged period of time, the inflammation in the gut can make its way to the brain, disrupting the integrity of the blood-brain barrier. Inflammation there can cause a "leaky brain," which furthers the mental health imbalance. One way that anti-depressants like SSRIs work is via anti-inflammatory mechanisms.

Here are a couple action steps you can take now for your gut - and mental - health:

• Eat fermented foods every day. These are going to be found in the refrigerated section of your grocery store, not on the shelves! 
• Work high fiber foods into your meal plan: legumes, artichoke hearts, avocado, flaxseeds, chia seeds and oatmeal are great ingredients to start with.
• Make bone broth with small joints, like chicken feet, necks and backs. When cooked slowly, glutamine (an amino acid that is used to repair inflamed cells in the small intestine) is broken down into an easily digested form. Sip bone broth every day or use it as a base for soups and stews, or use as a liquid for cooking whole grains and beans. 

These recommendations are not going to be appropriate for everyone, so it's always a good idea to consult a health care provider to get an individualized wellness plan. 



References

1. Uma Naidoo.This is Your Brain on Food (2020).
2. Baxter, M.G., Croxson, P.L. Facing the role of the amygdala in emotional information processing. Proceedings of the National Academy of Sciences of the United States of America. 2012 Dec;109(52):21180-21181. https://doi.org/10.1073/pnas.1219167110
3. Tynan, R.J., Weidenhofer, J., et al. A comparative examination of the anti-inflammatory effects of SSRI and SNRI antidepressants on LPS stimulated microglia. Brain Behav Immun. 2012 Mar;26(3):469-79. doi: 10.1016/j.bbi.2011.12.011.

Collectively, we have long understood the relationship between stress and the gut. Reflections on this connection shows up in common phrases, like "I get butterflies in my stomach when I'm nervous," and "I just felt me stomach drop with dread." Emotional strain can trigger digestive upset and has been shown to play a role in conditions like irritable bowel syndrome (IBS), the onset of inflammatory bowel diseases (IBD) and intestinal permeability (aka "leaky gut syndrome"). This relationship goes both ways: imbalances in the gut can trigger mood and cognitive imbalances too, including depression and Alzheimer's disease. 

The connection between the gut and the brain/heart is complex, so I'll be adding to a collection of blogs on the topic over the coming months. Click on "The Mind-Gut-Heart Connection" category to learn more. We'll start the conversation at the end of the digestive tract - in the colon - with the ever-amazing microbiota. 

There are bacteria and yeast living in and on your body. 

That's a good thing.

I sometimes joke that we need to look no further than these microorganisms sharing our bodies for the meaning of life: our purpose is simply to play host. Make them comfortable and well-fed. If we do that, we've got a good start on a good life. When our microbiome is healthy and robust, those bugs make nutrients for us, like short chain fatty acids and vitamins. They transform compounds in our food, like fiber and phytonutrients, into useful forms. They maintain our colonic environment and help us maintain digestive health. They communicate with and enhance our immune systems, and help us prevent disease. They even make neurotransmitters like serotonin and dopamine to facilitate positive thoughts and balanced emotions. 

So playing the role of a gracious host really does go a long way on our wellness journey!

The most accurate term for these bacteria and yeast living in and on our body is "microbiota," a term used interchangeably with "microbiome," though they are distinct words. "Microbiota" refers to the microorganisms found in an environment, while "microbiome" actually describes the collection of genetic material from said microorganisms. I might use these words interchangeably because "microbiome" is more commonly used and I think it's more important to see the big picture than get caught in the weeds. 

On the human body, there are microbiota found in the sinuses, respiratory tract and lungs, the mouth, the skin, and the digestive tract. The most heavily populated microbiota is found in the colon. In and on the human body, there are 10 times more microbiota cells then there are cells of human origin. In other words, there are ~150 times as many genes coming from microorganisms than from the human genome. (Learn more about the microbiota in Dr. Barrett's blog article here.)

Stressful encounters change the microbiota...and the microbiota changes the stress experience. 

Stressful experiences early in life inform the composition of the microbiota by impacting the type and abundance of microorganisms that colonize the colon. It is estimated that the microbiota is established by age three, so these early childhood experiences can have a lifelong impact on an individual's microbiota.

At all stages of life, beneficial microorganisms like Lactobacillus sp. decline in the presence of stress - even short-term stress. Lactobacillus is a genus of bacteria that is well-studied and easily found in over-the-counter probiotic supplements and fermented foods like yogurt. It's an important "bug" for many reasons, one of which is that it reduces inflammation in not just the digestive tract, but throughout the body. Repeated exposure to stressors has an exponential impact on Lactobacillus species and other beneficial microorganisms in the microbiota, giving us another reason to reduce stress and build resilience. 

Interestingly, the composition of the microbiota also impacts how a person responds to stress. Potentially pathogenic microorganisms, like E. coli, can trigger a heightened stress response. Similarly, a microbiota that is not diverse or abundant in beneficial microorganisms can also heighten the stress response. In other words, stress impairs the health of the microbiota. And a sick microbiota exacerbates the harmful impact of stress. 

Addressing gut health - including the health of the microbiota - is a necessary component of any functional nutrition plan. This becomes all the more important when lifestyle factors like stress and resilience (the ability to recover from stressful experiences) are indicated in the root cause of symptoms. Incorporating ferments, fibers, therapeutic probiotic therapy and nutrients that enhance the ecosystem of the colon may all be recommended to balance HPA axis imbalance, support recovery from burnout and enhance resilience. 



References:

1. Jeffrey D Galley, Michael C Nelson, Zhongtang Yu, et al. Exposure to a social stressor disrupts the community structure of the colonic mucosa-associated microbiota. BMC Microbiology 2014, 14:189.
2. Dinan, T.G., Cryan, J.F. Regulation of the stress response by the gut microbiota: Implications for psychoneuroendocrinology. Psychoneuroendocrinology. 2012 37(9):1369-1378 https://doi.org/10.1016/j.psyneuen.2012.03.007