Photo by Yaroslav Shuraev.

A few decades of research into the many benefits of a healthy gut microbiome have piled up evidence that a broadly diverse array of microbes inhabiting your gut leads not only to improved digestion but also to reduced chronic inflammation and resistance to disease. Now, an ongoing study is revealing more specific links between disease and lively gut health. 

A second brain

Somewhere between 200 million and 500 million neurons reside in the gut.

More precisely known as the “enteric nervous system” (ENS), and often casually referred to as a second brain or “gut brain”, our digestive tract is more densely populated with nerve cells than the spinal cord. Somewhere between 200 million and 500 million neurons reside in the gut, a small fraction of the number in the brain, but significantly more than the 100 million working within the spinal cord.

There is two-way communication between the gut and the other command center of the body, the brain. The vagus nerve is the main information highway between the ENS and the brain. This nerve is aided by other chemical signals produced by the gut and the immune system, which is largely housed in the gut.

The ENS acts independently from the brain to regulate digestion and also produces 90% of the body’s serotonin, a chemical with a wide variety of functions. Serotonin regulates and protects the digestive tract, helps tell the body when to fall asleep and when to wake up, plays a role in blood clotting, and influences appetite, among other things. Beyond these important duties, normal levels of serotonin have been shown to have a positive influence on mood. Anxiety and depression are lessened by healthy serotonin levels, while focus and emotional stability increase. 

Besides the well-established effects of serotonin levels, further studies are pointing to a person’s ENS being a kind of fingerprint or catalog of one’s personal history, as each of us has a unique gut brain reflecting our internal world’s interaction with the external world. From birth, a person’s ENS is contributed to by environmental and dietary factors, lifestyle choices, and chance encounters with disruptions from disease, trauma, and even some medications.

Gut dysbiosis

Gut health is linked to numerous health issues, many of which stem from chronic inflammation.

As research into this topic begins to tease out more specific evidence of a healthy gut being crucial to overall health, some recent results are paving the way toward better understanding and innovative treatments of all kinds of ailments.

An unhealthy ENS, also known as “gut dysbiosis,” was reported in the Journal of Functional Foods in January 2024 to have links to Alzheimer’s Disease. Further investigation is looking into the restoration of a healthy ENS as a possible treatment for Alzheimer’s.

New research into early signs of Parkinson’s disease suggests that the malformed protein “a-synuclein”, the presence of which is a characteristic of the neuro-degenerative disease, begins to gather in the gut long before the disease’s well-known motor symptoms manifest. This awareness could lead to improved and earlier diagnosis of Parkinson’s.

Because digestive distress is prevalent in those diagnosed with Autism Spectrum Disorder, 2025 research looked into understanding genetic links between the two issues, and further study is indicated to discover whether improved gut health can be used as a treatment.

ADHD patients also typically suffer from digestive distress. Gut dysbiosis throws off the production of serotonin as well as dopamine (a feel-good cousin of serotonin), leading to worsening of ADHD symptoms such as poor concentration and emotional dysregulation. Dietary treatments that improve gut health are being investigated and show promise as instruments in reducing the severity of ADHD symptoms.

Gut health is linked to numerous other health issues, many of which stem from chronic inflammation that results from ENS imbalances. Metabolic issues, poor nutrient absorption, autoimmune diseases, cardiovascular disease, fatty liver disease, skin issues, and chronic fatigue are just the beginning of a long list of conditions believed to be influenced or worsened by gut dysbiosis.

Strategy for a healthy gut

Each plant that you consume contributes its unique nutrient signature to our gut diversity.

Tuning up your gut health is best achieved by consuming a variety of foods that contribute to a maximum diversity of microbes.  A robust diversity of microbes makes you resilient in the face of disruptions caused by disease, infection, or drugs such as antibiotics (which we need to kill unwanted microbes, but which also temporarily wipe out many of the good guys).

One strategy for building and maintaining gut diversity that is gaining scientific traction is to consume 30 different plant foods each week. The average American currently falls way short of this mark, averaging somewhere between 8 and 15  different plants in a given week. Less diversity equals less resilience.

The origin of this strategy was a 2018 study called the American Gut Project, involving 10,000 participants from around the world whose gut microbiomes were analyzed. Results showed that those who consumed 30 or more different plants each week had a much more diverse presence of healthy gut microbes than those who consumed fewer than 10. A broader diversity also ensures production of short-chain fatty acids, which have been shown to decrease chronic inflammation, improve immune system function, and contribute to a steady metabolism.

Each plant that you consume contributes its unique nutrient signature to our gut diversity, enhancing our resistance to disease and, in some cases, aiding in the treatment of or recovery from certain conditions. 

We tend to repeat our reliable but narrow spectrum of menu choices, even if they are mostly healthy. However, a few tweaks on the shopping list can broaden our plant-based horizons in a way that is easy to adopt habitually. 

It’s not necessary to give up meat or dairy, or to increase your overall calorie intake. Merely replacing a few of your habitual choices with different plants will populate your microbiome with those plants’ uniquely beneficial phytonutrients and fibers, feeding a wider variety of desirable gut microbes.

Consider adding a variety of nuts and seeds to your diet. Switch up your whole grains and your legumes. Try some new veggies and fruits. Give your taste buds a treat by adding new and different herbs and spices.

Participants starting out with the 30 plants per week plan often keep a journal or a checklist to tally their consumption at first, but soon find that just a few adjustments incorporated into shopping and food prep routines will make this new habit an easy one to maintain.

We, and all of our 38 trillion gut microbe passengers, are in this together. The more the merrier.

Ann Constantino, submitted on behalf of the SoHum Health’s Outreach department.