Did you know that our gut is host to 10 times more bacteria than we have human cells? By number alone, we are more bacteria than human! Within your intestinal system live approximately 400 species of bacteria that number in the hundreds of trillions. It has been an accepted medical fact, proven by countless studies, that these bacteria influence our physical health in numerous ways. A growing body of evidence is now showing us that these bacteria also influence the way our brain develops and functions and impacts our mental health, mood, and emotional processing.
There is a significantly high rate of comorbidity, meaning simultaneous existence, between gastrointestinal disorders such as IBS, Celiac, and Reflux Disorder and mental illness such as depression, anxiety, OCD, and schizophrenia. One study shows that 70-90% of individuals with IBS have psychiatric comorbidity, most commonly major depression. Additionally, it has been shown repeatedly that individuals with depression, anxiety, and schizophrenia have abnormal varieties of bacteria in their gut flora.
Several studies have shown promising results of impacting mood disorders by changing gut flora makeup. The British Journal of Nutrition published a study showing that the addition of probiotics (capsules of healthy bacteria) for 30 days resulted in improved mood and reduced stress hormones. One fascinating study by McMaster University in Hamilton, Ontario changed the behaviors of mice by dosing them with probiotics to increase healthy bacteria or antibiotics to reduce the healthy bacteria. Mice exhibiting anxious behaivors such as defensive digging exhibited a reduction in those behaviors and exhibited more gregarious behaviors. Likewise, bold mice became timid when they got the microbes of anxious ones and aggressive mice calmed down.
It is clear that these microbes influence the function of our brain. What is less clear currently, is exactly how. The vagus nerve, a large nerve identified as the main highway of communication between the brain and abdomen, appears to play a central role. Researchers in Ireland found that upon cutting the vagus nerve of mice, the brain no longer responded to intestinal flora changes. It has also been observed that some bacteria produce neurochemicals previously unheard of which impact the brain in novel ways.
While we have a long way to go to understand the complexity of these systems and how they interact, it has become clear that the symbiotic relationship we have with our gut flora is vital to all aspects of our health. In my next blog post, I will review how to build healthy gut flora and avoid disturbing a normal balance of intestinal flora.