Evidence for the Gut-Brain Axis Continues to Accumulate

This crucial connection is redefining how we understand many diseases and treatments
January 23, 2020 Updated: January 23, 2020
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Good gut health is central to our overall health. For years, doctors and researchers thought that the delicate interplay between gut microbes, the immune system, and the cells lining the gut were solely responsible for this important balance. We have now discovered that nerve cells in the gut are critically important in this process as well.

That finding means that our gut has another direct connection to our central nervous system, further affirming the importance of the gut-brain axis.

In a recent study in the journal Cell, scientists at Harvard and Yale medical schools discovered that nerve cells within the intestinal wall release cytokines. Cytokines are a broad group of small proteins known as peptides. Cells use cytokines for signaling what is going on in their immediate environment.

Cytokines can spur cell development, immune modulation, and inflammation cycling. Cell signaling between the brain and gut is also carried out by hormones, neurotransmitters, growth factors, and—as the researchers discovered—cytokines.

The discovery that nerve cells in the intestinal wall have this communicative function is further evidence of the importance of the gut-brain axis. The gut-brain axis is the biochemical signaling that takes place between the gastrointestinal system and the central nervous system.

The importance of this connection has been a central tenet of functional medicine. Problems with this connection between our gut and brain should be evaluated early in a patient’s diagnostic workup.

One of the first digestive functions known to be controlled by the nervous system was peristalsis, the rhythmic contraction and relaxation of muscles used to propagate food from ingestion to excretion. The nervous system also controls the secretion of digestive enzymes and neurotransmitters. Now we can add the extensive and growing class of cytokines to that list.

The ability to communicate rapidly over long distances is one advantage to having the nervous system in charge of secreting these important cell signalers. This rapid communication becomes essential when you realize that the surface area of the average gut is 3200 square feet or approximately the size of a tennis court.

This discovery calls into question our current classification of organ systems.

The original distinction of our nervous, immune, and endocrine systems goes back well over 100 years ago and does not take into consideration new findings, such as this study. These are complex systems made of different organs, types of cells, and biochemical reactions. From a functional perspective, the neurons, immune cells, and hormones work synergistically in many instances. This finely tuned symphony of impulses, cells, and molecules work together as a single neuro-endocrine-immune system that performs daily life-sustaining functions. Regarding it as a single system would seem practical, especially since treating a part of it in isolation can disrupt its broader functions.

These findings may advance our choice of treatments for classical neurological disorders which many practitioners have clinically known for years to have strong connections with gut health. These include autism spectrum disorder, Parkinson’s disease, and Alzheimer’s disease, to name a few. Studies continue to find links between these diseases and aspects of our gut health.

Improvements in therapeutics would likely be seen in two categories. First, direct intervention using the nervous system itself or agents, such as a supplement, herb, pharmaceutical, or medical device, to alter the nervous system in order to impact gut health.

If we are able to alter cytokine profiles, for example, there could be a whole variety of conditions in the gut that could be modified to further an individual’s health.

The second improvement in therapeutics would be a more general shift in the way we see disease progression.

With tangible, experimental evidence supporting the concept of the gut-brain axis, it is now time to begin looking at many gut and neurological disorders from a different viewpoint. To what extent do all of them have some form of connection? Did the gut problem start the neurological problem or vice versa? This broader viewpoint may even enter the realm of everyday health. Did that poor quality fast food you ate for lunch affect how your cognition worked in the afternoon and evening?

Though research continues to expand our understanding of the importance of gut-brain access, this is unlikely to rapidly influence normal clinical practice. That said, functional medicine practitioners and other forms of medicine have long understood the importance of a whole-of-body approach to care, factoring in basic and essential aspects of lifestyle, like what we eat.

To that end, you’d be well advised to stop shopping for food based solely on price and taste and start thinking about how that food will affect your gut and then your brain and mind.

While the concept of the gut and mind being connected was commonplace for the nineteenth-century physician and patient, this connection was somehow lost over the past century. Now with the help of modern scientific inquiries, we return full circle from where we started: with a functional gut-brain axis critically important for our continued overall health.

Armen Nikogosian, M.D., practices functional and integrative medicine at Southwest Functional Medicine in Henderson, Nev. He is board-certified in internal medicine and a member of the Institute for Functional Medicine and the Medical Academy of Pediatric Special Needs. His practice focuses on the treatment of complex medical conditions with a special emphasis on autism spectrum disorder in children, as well as chronic gut issues and autoimmune conditions in adults.