Ever had a gut feeling? Most of us have. But what, exactly, do our guts have to do with our feelings?
I’ve blogged several times on the 75 percent of our bodies’ immune cells that reside within our guts. But our immune systems aren’t alone in sharing an intimate connection with them. We have what some researchers call, a second brain.
Meet the Enteric Nervous System, aka the Second Brain
Dr. Emeran Mayer, director of UCLA’s Oppenheimer Center for Neurobiology of Stress and Resilience, described gut feelings as proof of a “… complex, bidirectional communication system” between gut and brain.
He referred to the enteric nervous system (ENS), a meshlike web of neurons embedded in the gastrointestinal lining. The enteric nervous system extends from the esophagus to the anus. Its intricate connections to the brain have led researchers to dub the ENS “the second brain.”
Dr. Mayer explains:
“The ENS has been referred to as the ‘second brain,’ based on its size, complexity, and similarity – in neurotransmitters and signaling molecules – with the brain.”
Your brain and gut are in constant communication through the ENS.
We’re so accustomed to studying the body as a collection of separate systems that we often forget how interconnected they all are. Think about it! How often, when you experience mental distress, do you also have butterflies in your stomach?
Even before Dr. Mayer published his review, significant research had validated that stress affects our guts. For example, this 2008 study (Knowles et al.) tested the effects of academic stress on 23 healthy undergraduate students aged 18 to 44.
For two weeks (at the start of the semester and the first week of exams), sixteen women and seven men provided daily saliva and fecal samples. They also answered a questionnaire measuring their perceived level of stress.
On exam days, the researchers observed a big drop in “fecal lactic acid bacterial” levels that continued for six days.
Their summarized finding was that “… non”-extreme ‘everyday’ stress events affect the integrity of the… gastrointestinal microflora of humans.”
The Second Brain As a 2-Way Street
The second brain connection works both ways.
In a 2009 randomized, double-blind, placebo-controlled study (Rao, Bested et al.), researchers at the University of Toronto’s Department of Nutritional Sciences tested probiotics for treating people who had chronic fatigue syndrome.
For eight weeks, 39 participants in two groups received either a placebo or 24 billion cfu (colony forming units) of LcS (Lactobacillus Casey strain Shirota) daily. The LcS group experienced “a significant reduction in anxiety scores.”
In a similar double-blind, placebo-controlled, randomized trial published in 2010, French researchers (Messaoudi et al.) observed equally impressive results in their probiotic group.
Placebos (sugar pills) almost always make people feel better because they think what they’re taking might help their condition. That was true for the French study’s placebo group.
However, the probiotics group’s improvement was far more impressive: A 50-percent decrease in depression scores, compared to 15 percent for the placebo group!
The results of their interpersonal sensitivity scores measuring the ability to read nonverbal cues were even more revealing. The placebo group went in the wrong direction, with a 20-percent drop! In contrast, the probiotic group improved more than 50 percent.
Both groups’ overall average for all tested areas improved, but the probiotics group’s performance outshone the placebo group’s 49 to 24 percent.
The researchers concluded the study affirmed a strong connection between our gut microflora and our stress, anxiety, and depression levels. They also suggested that the second brain was part of the connection!
What Do These Studies Teach Us?
That our gut and its massive microbial population, our immune system, our brain, and our mental state are all interconnected!
We can’t overestimate the influence these three older studies have had on the current research landscape. The “gut-brain axis” has become a massive field of research.
This 2019 research review (Cryan, O’Riordan, et al.) acknowledged that “… the past 15 [years] have seen the emergence of the Microbiota… as one of the key regulators of the gut-brain function… This axis is gaining more traction.”
Does this mean that I should run out and buy a bottle of probiotics? Maybe, although it is best to get them in their natural state when possible.
After learning about the second brain, I’m more convinced than ever in the wisdom of eating what allows my gut to thrive: a variety of whole-food, plant-based ingredients!