Do you ever feel depressed or anxious or sad and can’t figure out why? Your circumstances and surroundings can definitely affect your mood but there’s an additional factor that plays a big role, and that’s what’s going in your gut. Your digestive tract contains millions of nerve cells, and communicates directly with your brain via the vagus nerve. That communication is a two way street: your brain influences the motility of your gut, secretion of digestive enzymes, nutrient delivery, and helps stabilize the community of bacteria that call your gut home. Your gut plays an equally important role: many of the neurotransmitters that control your emotions, like serotonin and dopamine, are actually made in your gut, not your brain, and that means the health of your GI tract – and it’s trillions of worker bee microbes – can have a big impact on your mood and behavior. 

That’s why antibiotics, which destroy massive numbers of your gut bacteria, and GI infections that disrupt the microbial balance in your gut can have such a profound effect on your emotions. You can induce anxiety in lab mice by inoculating them with Campylobacter jejuni, a common intestinal pathogen. I see the same phenomena in some of my patients after they’ve had a gastrointestinal infection – many of them describe an increase in anxiety and depressive symptoms long after they’ve recovered from the acute gastroenteritis. And it’s not just acute events like an intestinal infection or a course of antibiotics that can induce these changes; chronic GI conditions like irritable bowel syndrome and inflammatory bowel disease are often accompanied by mood disorders.

In addition to producing neurotransmitters, your gut bacteria have other strategies for influencing your emotions. One of the ways they can affect your mood is through their metabolic byproducts. Gut bacteria ferment indigestible plant fiber from your diet to create byproducts like short chain fatty acids (SCFA). Butyrate is a SCFA that is neurologically active, and has been shown in clinical studies to reduce symptoms of anxiety and depression. I see this every day in my medical practice: when I recommend a high-fiber diet to improve inflammation in the gut, my patients’ mental health and mood often improve right alongside their GI symptoms.  

People with various psychiatric disorders, including schizophrenia and depression, have been found to have significant changes in their population of gut bacteria compared to healthy individuals. Chronic stress and elevated levels of the stress hormone cortisol can also negatively impact the microbiome. Scientists in Belgium working on the Flemish Gut Flora project were able to catalog and determine which specific bacteria are most strongly correlated with quality of life and depression, providing more clinical evidence to support the link between what’s going on in your gut and how you’re feeling. 

As we learn more about the complex and intimate relationship between the brain and the gut, it may be that the future of psychiatric care will include high-fiber foods in addition to (or instead of) prescription medications. Eat a salad and call me in the morning!