What does your gut have to do with mental health? It turns out: there’s a factual, physical basis for the colloquial “gut feeling” phenomenon.
In the last few years, a tremendous amount of literature has come out of top research institutes supporting the notion that the gut – our intestines, stomach, and the microorganisms that live there – has measurable, direct effects on brain chemistry. There is now abundant research suggesting an ancient relationship between the brain and gut, which communicate via the nervous system, hormones, and our immune system.
In order to have a full appreciation of the scope of this discovery, you’d need degrees in endocrinology, immunology, pathology, and neurology… far beyond the purview of a blog post. But you can trust reliable measurements from thousands of brilliant doctors, all agreeing on one central fact: that there is a direct relationship between one’s overall gut health and their overall mental health.
One of many recent discoveries, in particular, underscores the importance of this phenomenon: Serotonin, or 5-hydroxytryptamine, a neuromodulator that occurs endogenously in the bodies and brains of most animal species, is used for regulating emotional state, sleep, and digestion. Among the more essential aspects of life, it is one of the animal kingdom’s most basic and often-replicated chemical messaging systems. And ninety-five percent of the serotonin that humans need is produced by microbes that naturally occur in the gastrointestinal tract.
Here’s another potentially disturbing fact: every gut is sterile at birth. But after a few years in the world, the single-cell organisms that live in your body will outnumber your own cells 10 to one.
Most of them are helpful bacteria. And while they live nearly everywhere in the body, 100 trillion of them like it best in our gut. Which has, in turn, evolved a fantastically-complex, living, autonomous neural network based on the chemicals these bacteria secrete. That’s right: the gut is the only organ in our body with an independent nervous system. An intricate network of 100 million neurons lines the interior of the gut wall. Even when the Vagus nerve – the main nerve connecting the gut to the brain – is severed, a person can survive, and the gut continues to function. However, when that nerve is severed, the effects of gut bacteria on brain chemistry quickly disappear.
But it’s not just the presence of helpful bacteria that change behavior. In one of the earliest studies on the gut-brain relationship: laboratory mice exposed to Campylobacter jejuni, a single strain of pathogenic bacteria, became more anxious after just two days – refusing to enter exposed areas of their habitats. But in a follow-up study, mice fed lactobacillus rhamnosus, a helpful probiotic, were more willing to enter exposed areas and even swam better. A probiotic diet seemed to protect the mice from the effects of stress – showing a significant reduction in the hormone corticosterone and an increase in gamma-aminobutyric acid, or GABA – a neurotransmitter that moderates our flight-or-fight response. It seemed that
So how is it, exactly, that gut bacteria influence the brain and behavior so profoundly? We know that the Vagus nerve plays a vital role in absorbing neurotransmitters produced by the gut and passing those messages along to the brain. But other studies suggest that the immune system plays a role – with chemical communication occurring directly between bacterial cells and immune cells, propagating throughout the body. In any case, it’s incredible – and no coincidence – that the bacteria which live in our gut both produce and respond to the exact same set of neurochemicals that the brain uses to regulate mood, cognition, sleep, and stress.
We’re probably a long way out from being able to analyze, directly, the contents of an individual’s gut. Experts estimate roughly 10-15 years before targeted, proven, and effective probiotic treatments are commercially available to the public. Even further out are gut-based treatments for depression and anxiety. Still, the scientists pursuing this line of research are becoming increasingly confident that, to understand our emotions and behaviors fully, we need to understand how our gut “thinks.”
It’s an exciting, entirely new frontier in medicine.