Over the past decade I’ve been reading and thinking quite a bit about the etiology and pathophysiology of mental illnesses such as chronic depression, autism, and attention deficit disorder. Throughout this process it has become increasingly clear to me that mental illness typically doesn’t start in the mind, but rather, in the gut.
This statement goes against what conventional wisdom tells us to be true; hence, a lot of people probably question its merits. Not everyone though. Those who’ve kept up with the scientific research pertaining to the gut-brain axis are probably on board with the idea that intestinal health is intimately linked with mental health and that psychiatric illness often starts in the gut.
The links between evolutionary mismatch, gut function, and brain health
In my recent article entitled The Darwinian Causes of Mental Illness I made the case that the main reason why a lot of contemporary humans don’t operate at peak capacity, mental health wise, is that we find ourselves in the midst of an evolutionary mismatch situation. We’re subjecting our bodies to inordinate amounts of evolutionarily novel stimuli, which alters the exposures of our brains and leads to chronic activation of bodily systems that initially evolved because they helped our ancestors survive and reproduce in the natural environment in which they lived.
One principal way by which mismatch initiates the development of mental illness is through its effects on gut function and health. By altering our environment and way of life, such as by creating and eating absurd amounts of highly processed foods and routinely using drugs with antibiotic properties, we’ve altered our microbiotas and the workings of our guts, something that has made us more susceptible to mental illness.
A big pile of scientific research links gut dysfunction with everything from depression to Alzheimer’s disease to autism (1, 2, 3, 4, 5, 6). The cautious scientist will be quick to point out that there’s still a way to go in terms of establishing causal relationships in some cases. Science moves slowly and it doesn’t always bring about firm, definite answers to the questions we want answered. What’s important to point out is that when I make statements about diet, health, or anything else really, I don’t just consider what scientific studies show, I also take into account my own experience, the observations I’ve made over the years, and my own and others’ clinical experience, among other things. Based on all of this, my conclusion is that the gut is at the center of the etiology of many mental disorders.
Perhaps needless to say, gut dysfunction isn’t the only issue that can bring about mental ills; other things, such as social isolation and traumatic life events, can obviously also trigger anxiety, depression, and/or other similar issues. With that said, I strongly suspect that gut dysfunction is the fundamental cause of the epidemic of mental illness that’s emerged in recent human history.
A healthy gut is a prerequisite to a healthy brain
I first started to suspect that the key to a well-functioning brain may lie in the gut a long time ago; however, it wasn’t until I came across the book Gut and Psychology Syndrome, written by Natasha Campbell-McBride, that I became truly convinced that a healthy gut is a prerequisite to a healthy brain. In the book, Dr. McBride details her work with children suffering from mental illness. She discovered through her clinical practice that several mental disorders frequently overlap, in the sense that it’s not uncommon to be afflicted by more than one condition, and that pretty much all of her patients suffered from gut problems.
As a result of these observations, she started exploring the possibility of treating mental illness through the gut, something that bore fruits, in the sense that she discovered that many cases of mental disease could be partly or fully remedied via gut-targeting interventions. I question the merit and viability of several of the treatment approaches she outlines in the book; however, I certainly don’t question her fundamental belief that the gut is intimately linked with the brain.
In the time that has passed since I read that book, my conviction that gut dysfunction is at the root of many cases of mental illness has only strengthened. Not just because a number of scientific articles pointing to this conclusion have been published, but also because I’ve noted, as I’ve observed how people function, look, and behave, that there’s a clear association between gut health and mental health. The function of one’s gut influences a variety of processes in one’s body and contributes to controlling one’s appetite and physical appearance; hence, if one knows what to look for, one will start to notice patterns pertaining to the workings of our guts and our brains.
Personally, I’ve found that my gut greatly affects my cognitive function and mental health and well-being. If my gut for some reason is in bad shape, then my brain is going to be in bad shape as well.
How can the gut affect the brain?
There are many different pathways by which dysbiosis and gut dysfunction can cause mental disturbance. Gut bacteria produce a variety of brain-stimulating compounds, as well as regulate host production of substances that are known to affect mood and behavior, such as serotonin (7). The gut also communicates with the brain via the vagus nerve and is a critical component of the immune system, which is known to be tightly linked with the brain. There’s a reason the gut is called the second brain.
As I pointed out in my previous article on mental illness, people who suffer from mental disorders such as chronic depression typically have elevated levels of inflammatory cytokines in their bodies. Not only is a chronically inflamed body more susceptible to inflammation-related disorders of the brain than a non-inflamed one, but it’s also more prone to infections, including parasitic invasions, something that can trigger or contribute to causing mental illness (8, 9).
It’s time we start treating mental illness through the gut
It’s not long ago that scientists and health professionals who claimed that conditions such as autism and attention deficit disorder are caused by dysbiosis and who treated people with these conditions via the gut were labeled as quacks by the medical establishment. Many mainstream doctors and psychiatrists are still stuck in their old ways of doing things and probably reject the idea that gut health has anything to do with mental health; however, on a more positive note, the watershed of research that’s been published on the gut-brain axis over the most recent decade has triggered a number of health professionals and scientists to rethink their beliefs and practices.
It’s becoming increasingly recognized that psychiatric medications don’t address the root causes of the conditions they are prescribed for, but rather merely mask symptoms of a deeper problem, and that psychotherapy only gets one so far. It’s certainly possible to change the way one thinks, feels, or behaves by deliberately making an effort to do so, at least to some extent; however, it’s important not to forget that that our brains are products of natural selection that are greatly influenced by biological inputs.
The “new” scientific discovery that the gut is intimately linked with the brain has profound, widespread implications and can – and should – usher in a paradigm shift in psychology and medicine. The dogmatic belief that the brain is largely separated from the rest of the body – a notion that has shaped the workings of modern psychology and psychiatry – is long outdated. In my opinion, it’s long past time that gut healing and microbiome restoration, which includes species-appropriate nutrition, become a routine part of the treatment of most, if not all, mental health disorders. Moreover, it’s long past time that principles of evolutionary psychology are more widely incorporated into mental health education and care.