Ten years ago, if you had asked a neuroscientist are we on the right path to understanding the inner workings of the brain, she probably would’ve gave a hearty “Yes!” But more recent research calls a lot of older assumptions about the brain — and in fact, the whole body — works.
We’re only now beginning to understand that the brain doesn’t stand alone in being responsible for our thoughts and emotions. Instead, new research is shedding light on how the gut and the bacteria that call it home have a much bigger role to play than anyone had ever suspected.
Scientific research into the ways our gut and brain interact have been ongoing now for over a decade. To date, a lot of the studies examining the brain-gut connection have either used animal studies or small pilot studies on just a handful of humans. Research like this can give us clues and help guide future research direction, but it can’t really answer the big questions of how strong the connection is, what’s its purpose, and how does it work.
That is, until recently. A study published earlier this year in the journal Nature Microbiology examined more than 1,000 people who were enrolled in Belgium’s Flemish Gut Flora Project — a project specifically designed to answer questions like these. In a job that would be considered one of the least sexiest ever, the researchers used DNA sequencing to analyze microbiota in the subjects’ feces.
In an accompanying editorial, the journal notes, then the researchers took it one step further and “validated the findings in an independent cohort of 1,063 individuals in the Netherlands’ LifeLines DEEP project. Finally, they mined the data to generate a catalogue describing the microbiota’s capacity to produce or degrade molecules that can interact with the human nervous system.”
That means the correlational findings made by the scientists are robust. And what exactly did they find?
The researchers found that two groups of bacteria, Coprococcus and Dialister, were reduced in people with depression. And they saw a positive correlation between quality of life and the potential ability of the gut microbiome to synthesize a breakdown product of the neurotransmitter dopamine, called 3,4-dihydroxyphenylacetic acid.
They also found that the bacteria Faecalibacterium and Coprococcus were both more common in people who rated more highly on a self-report of mental quality of life. Both types of bacteria appear to be responsible for breaking down dietary fiber in order to produce an anti-inflammatory compound called butyrate. In case you forgot, the gut is responsible for most of our immune system’s response (as well as producing the vast majority of serotonin).
What Does This Mean for Your Mental Health?
This large scientific study is an important reminder of how the brain and body are interconnected in ways that we’re only now beginning to understand. You can’t think of your brain as some sort of stand-alone organ — it’s an integrated part of a holistic system. When you treat your body badly, your brain — and its accompanying emotions and thoughts — will also suffer.
This also helps to begin to explain why diet and exercise have been shown to help people with mental health concerns, even serious ones such as depression. A balanced diet that includes lots of fiber helps keep your gut system running efficiently by helping to support a more diverse gut microbiome. And exercise helps keep your body’s internal systems like this one running well and as they were designed.
Since this was a correlational study, we can’t say whether these changes in bacteria cause depression or other mental health concerns, or are simply a byproduct of having such disorders already. But it doesn’t really matter since most of us could benefit from watching what we eat more anyway — especially if it might benefit our emotional health.
Most people don’t need to change their diet or add probiotics or supplements to them, as long as you eat a balanced diet that includes a healthy daily dose of fiber every day. Also, a diet that is low in processed foods can help, avoiding things like eating lunchmeats or virtually anything in the frozen food section of the grocery store (outside of frozen vegetables). Your diet should also be rich in plant foods — things like fruits and vegetables, grains, as well as legumes and nuts.
Valles-Colomer, M. et al. (2019). The neuroactive potential of the human gut microbiota in quality of life and depression. Nature Microbiology, 4, 623–632. https://doi.org/10.1038/s41564-018-0337
Nature editorial. (2019). Links between gut microbes and depression strengthened. Nature, 566, 7. doi: 10.1038/d41586-019-00483-5