Why Your Gut is Your “Second Brain”
Your gut is lined with over 100 million nerve cells
Digestion is a carefully orchestrated process, which is why you have so many brain cells down there. The gut is not a glamorous organ. You might hear people say I want to dedicate my life to become a cardiologist or a neurosurgeon, but very few people want to dedicate their lives to study the gut. A significant part of the body, hitherto relatively unexplored.
Apart from extracting energy from the food we eat, the gut accounts for most of our immune system and produces more than a dozen hormones that influence everything from our appetite to our mood.
Buried in our intestines, deep inside its tissue, is a very thin layer of the brain. It’s called the enteric system and comprises the same cells, neurons found in the brain. There are over 100 million neurons in the gut, except instead of being in one big lump, like the brain, the neurons in your gut are spread in a thin mesh that extends from your throat to your rectum.
The ‘second brain’ doesn’t do much trigonometry or worry about tax returns, but it does orchestrate digestion, moderate gut pain and develop the glorious immune system.
Fun fact 1: When we talk about having “gut feelings” or “gut instincts,” we reflect the reality of how closely our guts and brains are entwined.
The Gut Microbiome
The star of the digestive show is the one to two kilos of microbes that live in your gut and make up the microbiome.
Until biotechnology came along, these little guys were almost impossible to study. All we knew was they protected the gut from dangerous invaders, synthesized a few vitamins, and gobbled up the fiber our bodies can’t digest. Now we know far more than that.
All kinds of connections from how stress can affect your intestines’ microbial makeup to how the microbiome affects behavior. There’s a reason why funding agencies are pouring millions of dollars into understanding what researchers call the gut-brain axis.
The Gut-Brain Axis
The gut-brain axis is a two-way link between our CNS (Central Nervous System — controls functions of the body and mind), and the ENS (Enteric Nervous System — controls functions of the gastrointestinal tract).
A complex channel of communication signals between the endocrine (hypothalamic-pituitary-adrenal axis), immune(cytokine and chemokines), and the autonomic nervous system (ANS) is involved in the gut-brain axis.
With the help of the GBA neuro-immuno-endocrine conciliators, the brain can influence intestinal function with immune cells, epithelial cells, enteric neurons, and smooth muscle cells.
The cells of the gastrointestinal tract are under the influence of the gut microbiota. The microbiota is the microbe population in a specific ecosystem within the body, such as the population found in the gut microbiota or skin microbiota.
The microbiome’s bacterial DNA is approximately ten times greater than the human genome*, altogether, which explains why scientists label the microbiome as a “superorganism.”
*A genome is an organism’s complete set of DNA, including all of its genes. In humans, a copy of the entire genome — more than 3 billion DNA base pairs — is contained in all cells that have a nucleus.
With the rise of modern antimicrobial treatments, overuse of disinfectants, harsh cleaning products often marketed as necessary for better health. To understand the adverse effects of these, the Human Microbiome Project was set up to understand the unique interdependent co-evolution of humans and microbes and the role they play in health and disease.
The Gut-Brain Link
When we spent nine months in our mother’s womb, we were in an essentially sterile environment. As we enter this world, we are smothered in an invisible coating of microbes and friendly microbes, too, from our mother’s birth canal.
According to research studies, the composition of the gut microbiota from infancy is the fundamental building block of development and maturation of the human CNS and ENS.
The GI mucosal lining and the gut microbiome always harmoniously interact with each other, and this also helps in tuning the development of the immune system. With more and more research conducted, with lab mice, the effects of antibiotics, probiotics, and fecal transplants to determine the impact of the gut microbiota on our brain and behavior.
Fun fact 2: Lymphoid tissues are organized tissues that support immune responses. The gut-associated lymphoid tissue (GALT) comprises 70% of the body’s immune system and is the body’s largest immune organ.
This second brain of ours might not be the best at remembering poetry, but it does play a big part in influencing emotions by the nerves in our gut. Getting butterflies in your stomach is just one example of how our gut reacts to physiological stress. Everyday emotional well-being may rely on messages from our brain below to the brain above.
Mindful of the similarity between both our brains, several studies were conducted to determine the correlation between psychological issues such as depression, anxiety, autism, and multiple sclerosis to how our gut responds to it. Treatment for depression targeted towards the mind unintentionally affects our gut.
Let’s understand this; more than 30 neurotransmitters are used in the ENS (Enteric Nervous System), just like our brain. Also, 95% of serotonin — the feel-good hormone is produced in our digestive tract. Antidepressant medications, otherwise known as selective serotonin reuptake inhibitors (SSRIs), increase serotonin levels. No wonder medicine that is meant to cause a change in the mind often causes gastrointestinal issues as side effects.
An example of this is the Irritable Bowel Syndrome (IBS), which affects more than two million Americans happens because of an excess of serotonin secreted in our gut.
Manipulating the gut microbiome
Since microbes are easy to manipulate and eliminate, they can be readily modified for better functioning, regulatory control, targeting, and even delivering. Maintaining a good and balanced relationship with them is important.
Many factors affect our microbiome, including how we are born, by C-section or not. Babies born by a C-section don’t get initial inoculum or coating of bacteria designed by evolution to be in the mother’s birth canal. Instead, they are first coated with other bacteria on the skin or in the hospital environment, contributing to a 25% increased risk of obesity, asthma, immune deficiencies, and inflammatory bowel disease in later life.
Environment, antibiotics, stress, and our diet modify our gut microbiome, giving it a diversified flora. Out of these, diet is emerging as one of the leading influences on our gut’s health, a factor we have complete control over.
We can manipulate the balance of our microbes by paying attention to what we eat. While we already know that the microbiome helps in digestion, it also affects your brain.
By being mindful of how we fuel and feed, our gut will eventually improve our body; think of our gut as the engine that drives us, we always ensure to fuel it rightly.
Our gut loves fermented foods rich in probiotic bacteria such as yogurt, sauerkraut, kimchi, kefir, miso, kombucha, etc. Adding beneficial bacteria and enzymes to our overall intestinal flora reduces cortisol (the stress hormone) levels.
Eating more whole foods — vegetables and fruits high in fibre and antioxidants, getting enough sleep, and exercising regularly contributes to the healthy gut microbiome. Our bodies are miraculously phenomenal.
Think about everything you do as affecting your microbiome; think about how you can improve it. Think twice.