Welcome to week two, where we will discover that our gut is more than a place to digest food for fuel. We’ll learn the various means of communication pathways that flow from the gut to the brain, the guts vital role in our immune system, and its relationship with our endocrine system - which all have ties to our mental health.
The Gut-Brain Connection:
The gut-brain connection communicates in a variety of ways.
Vagus Nerve - the longest nerve in the body, connects our brain to many organs, including the intestines, stomach, heart, and lungs. It is a key part of our parasympathetic nervous system - rest and digest. Influencing breathing, digestion, and heart rate - which all have a huge impact on our mental health. 80 - 90% of nerve fibers in the vagus nerve are for transmitting information from the gut to the brain, rather than the brain to the gut. 1
Microbial Metabolites - Chemical compounds that communicate with cells to serve as messengers. These chemical messengers are utilized for gut function and nerve activity, never crossing the blood brain barrier, yet influence brain function. The Gut produces: - 90% of the body’s serotonin -50% of the body’s dopamine - 99.5% of the body’s melatonin
Influence how neuro-chemicals are produced
Have a negative impact on energy production and cellular death
Impacts stress hormones (specifically cortisol)
Proliferates cytokines - increasing likelihood for even more depression 2
Understanding the Guts Role in our Immune System:
Thanks to the Human Microbiome Project we are learning that our immune system and the root of our mental health actually live in and around our gut (called GALT - gut-associated-lymphatic tissue).
Up to 80% of our body’s immune system is accounted to GALT 3
Why? The intestinal wall is the barrier to the outside world - aside from the skin it has the most chances for bodily defense.
Any potentially harmful substance in the gut will send a message to the rest of the immune system. This is one reason food choices are so important.
The Microbial Flora in our Gut Has Many Roles and Duties:
Aides in absorption of nutrients
Creates a barrier from harmful invaders (bad bacteria, viruses, and parasites)
First step of detox
Production of enzymes, vitamins, amino acids, and neurotransmitters
Help stabilize stress hormones
Regulates inflammatory pathways
The gut is our biggest immune organ - controlling the immune systems response
Understanding the Way the Gut Works With our Hormones:
Gut microbiota is a key factor in the metabolism of hormones, and those hormones greatly influence our microbiota.
Gut hormones identified in mood disorders such as anxiety and depression serve as signals in the gut-brain axis as well as our energy metabolism. All of these hormones are released in response to food in-take and work to regulate different functions of our central nervous system. Making the endocrine system the other factor identifying what is going on between our brain and our gut. 4
Hormones and Your Central and Enteric Nervous Systems:
Central Nervous System (CNS) connects the brain to the spinal cord.
Enteric Nervous System (ENS) runs from the mouth to the anus - same neurons and neurotransmitters found in our CNS.
The ENS communicates with our brain through the nervous system and our hormones.
Both CNS and ENS are connected via the vagus nerve.
Gut microbiota can exert considerable influence on our CNS. Microbiota have the ability to produce neurotransmitters that are essential for mental well-being.
The CNS helps regulate the intestinal function via the hypothalamic-pituitary-adrenal axis (HPA).
Stress produces a cascade of events in the HPA axis. The HPA axis is a self-regulatory system using cortisol to regulate its own activity through a negative feedback loop. Changes in the HPA axis loop affect many physiological systems. Chronic stressors also affect the release of hormones such as norepinephrine and serotonin, pro-inflammatory cytokines and inflammatory pathways in the brain, endocrine glands and blood.
Cortisol is the body’s stress hormone, and also controls how our body processes carbohydrates, fats, and proteins.
Excess cortisol over time can lead to excess abdominal fat, bone loss, suppress immune system function, fatigue, increased risk for insulin resistance, heart disease, and depression. 3
Cortisol is also a buffer against inflammation - when cells become resistant to cortisol one result is chronic inflammation. 5
Healthy Gut - Healthy Mind:
Our gut is home to trillions of bacteria called our microbiome. Our microbiome allows for nutrients to enter the body, keeping opportunistic pathogens out, and helping our brain function. The gut microbiome ecosystem are key players in our mood and overall mental health; helping with depression and anxiety, but can also make matters worse. If our microbiome is out of balance (dysbiosis) that will effect our overall mood. Knowing the relationship between the vagus nerve explains why stress can play a role on our digestion and why digestive issues play a role in our mood. When the vagus nerve is impaired by stressors it cannot react adequately to inflammation. To support our health our microbiome needs to be diverse. Diversity is what helps keep it in balance. Dysbiosis results in opportunistic bacteria to proliferate and ultimately cause inflammation, which can contribute to depression and depression can cause inflammation.
At its basic level our diet can help our gut microbiome protect our mental well-being because the right food feeds the right bacteria. When you eat plenty of healthy diverse foods, our microbiome is more diverse and is able to generate neurotransmitters.
By now I hope you are seeing the relevance akin to the systems in our bodies. Next week, join me for blog #3 - where we will be looking into the role inflammation and inflammatory foods have on our mental heath well-being.
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Himmerich H, Patsalos O, Lichtblau N, Ibrahim M, Dalton B. Cytokine Research in Depression: Principles, Challenges, and Open Questions. Front Psychiatry. 2019; vol 10: 30. doi: 10.3389/fpsyt.2019.00030.
Brogan K MD, Loberg K. A Mind of Your Own. Thorsons. 2016.
Sun L, Li J. Nie Y. Gut Hormones in microbiota gut-brain cross talk. Chin Med. 2020; vol 133(7): 826-833. doi: 10.1097/CM9.0000000000000706.
Cohen S, Janicki-Deverts D, Doyle W, Miller G, Frank E, Robin B. Chronic stress, glucocorticoid receptor resistance, inflammation, and disease risk. Proc Natl Acad Sci USA. 2012; vol 109(16): 5995-5999. 10.1073/pnas.1118355109.