Until recently I believed that mood, feelings, and personality were solely the result of my brain. When I felt anxious, stressed, or unexpectedly joyful, I thought it was from the neurotransmitters in my brain.
But modern science is uncovering a startling, humbling reality: the gut plays a major part in our moods.
The gut profoundly affects mood and depression through the gut-brain axis—a two-way communication network. The gut microbiome produces roughly 90% of the body’s serotonin as well as other vital neurotransmitters. While the neurotransmitters in the gut cannot cross the blood-brain barrier, the gut can signal the brain to produce these and other chemicals.
For decades, the fields of psychiatry, neurology, and gastroenterology were studied as separate islands. But the discovery of the importance of the gut has linked these areas of research.
Inside our digestive tract is an ecosystem of close to 39 trillion bacteria, viruses, and fungi known as the gut microbiome. Microbes in our intestines synthesize key brain chemicals in addition to serotonin, including dopamine, and GABA that aid in digestion.
The primary physical link between the gut and the brain is the vagus nerve, a large cranial nerve that goes from the brainstem to the abdomen. It functions like a bidirectional cable, allowing constant, split-second communication between our head and our gut. Digestive distresses—from Irritable Bowel Syndrome (IBS), Crohn’s disease, constipation, and other inflammatory gut issues—send stress signals to the brain via the vagus nerve.
What is truly surprising is that about 80% to 90% of the fibers in the vagus nerve send signals up from the gut to the brain, rather than the other way around. When our microbiome is balanced, it produces an array of neurochemicals that signal safety and calm. But when that ecosystem is unbalanced, it fires distress signals up the vagus nerve, manifesting in our brain as anxiety, brain fog, depression, and irritability.
The psychological influence of microbes isn’t restricted to what is happening inside our bodies; it also comes from physical contact with the earth.
For example, Mycobacterium vaccae is a harmless, microscopic bacterium found in healthy soil. In neuroscientific studies, researchers discovered that when mice were exposed to this microbe, it triggered a surge of serotonin in the brain. The behavioral effects were mirror-images of prescription antidepressants. The mice became more resilient to stress and less anxious. It helps explain why many find gardening relaxing.
For most of human history, our ancestors lived in an environment where they were covered in soil microbes. Humans forged for food, farmed with bare hands, and lived in constant contact with the earth. Today, we live in a sanitized world, using antibacterial soaps, living in homes, and working in offices. We have isolated ourselves from the microbial allies that can keep our microbiome in check, but we have also isolated ourselves from microbes that can cause serious illnesses.
Since our moods are affected by our microbiome ecosystem, it means we have the ability to aid our mental health. Scientists recommend that we consume prebiotics such as complex, fibrous carbohydrates (e.g., oats, asparagus, onions, and bananas). Live fermented foods (e.g., yogurt) also introduce beneficial chemicals into our system.
The realization that our minds are tethered to our gut is a surprise to scientists. But when we are feeling off balance, it could be something that we can aid by consuming foods (or taking vitamins or medicines) that support a healthy gut.
Happiness isn’t just something that we can will—it’s also a byproduct of a working ecosystem.
Angela Rieck, a Caroline County native, received her PhD in Mathematical Psychology from the University of Maryland and worked as a scientist at Bell Labs and other high-tech companies in New Jersey before retiring as a corporate executive. Angela and her dogs divide their time between St Michaels and Key West Florida. Her daughter lives and works in New York City. Angela Rieck, a Caroline County native, received her PhD in Mathematical Psychology from the University of Maryland and worked as a scientist at Bell Labs and other high-tech companies in New Jersey before retiring as a corporate executive. Angela and her dogs divide their time between St Michaels and Key West Florida. Her daughter lives and works in New York City.
