Most individuals not engaged in the pursuit of an education rooted in science might still conceive of human biology as a collection of non-interactive systems housed inside a skin, but this ignores the brain and gut connection. As research proves repeatedly, this understanding of the species’ biology is reductive and overly deterministic. Published studies delineate with increasing frequency the interconnectedness of biological systems. When one takes a moment to examine the evidence, such relationships become apparent. This article explores the gut-brain axis in humans and its implications for medical research.
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Anyone familiar with the famous phrase,“You are what you eat” should take note. Within the human gut or large and small intestines exist billions of microorganisms. If one is looking for perspective, each organism is single-celled, and collectively they represent a population about ten times greater than the total number of cells that make up the human in which they reside. That’s a lot of cells. What are they doing in there? What are their roles in individual human health? How are they connected to the brain, precisely? These are simple questions with complicated answers.
First, scrub the concept that the brain all the way up in the skull has no concrete or direct interaction with the intestines. Studies in the recent past have shown that there are neurons in the stomach and that serotonin is produced mainly in the gut as well as in the brain. But wait, isn’t serotonin a neurotransmitter? Aren’t neurons the structures responsible for thought? Yes, and yes, but that’s not the weirdest part of what scientists are discovering. Welcome to the gut-brain axis.
The composition of the microbiome influences mood, behavior, and even predisposition to allergies, autoimmune diseases, and autism spectrum disorders. What one feeds it is vital, but as an article published by Johns Hopkins Medicine indicates, the Standard American Diet is doing a terrible job of feeding the good bacteria. Add a sedentary lifestyle and a high-stress working environment and the increasing numbers reported for mental illness, depression, anxiety, and even motor neuron diseases like ALS cease to be quite so mysterious.
In the walls of the digestive system there hides a second brain. It doesn’t look anything like the first one upstairs, but it does control for mood, perspective, and some crucial aspects of general human health. This is known as the enteric nervous system (ENS) and is composed of 100 million nerve cells that line the human alimentary canal from mouth to anus. It combines the sympathetic and parasympathetic nervous systems, and it also has a direct line to the Big Brain.
For decades, it was believed that individuals suffering from a variety of digestive issues were doing so because of an underlying condition of depression or anxiety—that the brain was impacting the digestive system. So, they medicated the depression or anxiety. When the digestive problems persisted or worsened, they were at a loss to explain why. The reason is that the brain and gut connection isn’t a one-way street.
As research continues to unveil the many ways in which the ENS and the gut microbiome impact individual mental and physical health, there are essential lessons society may glean. First, the deeply interconnected nature of seemingly disconnected systems may have implications for other areas of medicine and biotech. It may also influence how artificial intelligence is designed. Even so, it’s also important to remember to feed the gut as well as the human that surrounds it. Increasing evidence for the brain and gut connection has shown that neglecting it may have serious consequences.