Q6 Ways to Explain the Gut-Brain Connection to Skeptical Patients

One of the most effective ways to explain the gut-brain connection to skeptical patients is to describe the gut and brain as two departments in the same organization that constantly exchange information. When one department experiences a problem, the other can feel the effects, even if the connection is not immediately obvious. I explain that the gut and brain communicate through the nervous system, hormones, and immune signals. For example, stress can affect digestion, causing stomach discomfort or changes in bowel habits. Similarly, digestive discomfort can influence mood, concentration, and overall well-being. The evidence I find particularly helpful is the well-established relationship between stress and gastrointestinal symptoms, especially in conditions such as irritable bowel syndrome (IBS). Research also shows that psychological therapies, including cognitive behavioural therapy, can help some patients manage IBS symptoms. The biggest difference comes from using familiar experiences instead of complicated medical terminology. Most people have experienced butterflies in their stomach before an important event. Connecting that experience to the science makes the relationship easier to understand. The key lesson is to explain the connection without exaggerating it. Gut health and mental health influence each other, but not every digestive problem is psychological, and not every mental health concern begins in the gut. Clear, balanced explanations help build trust and encourage informed healthcare decisions.

As a neurologist and sleep medicine physician, I would describe the gut as something like a sense organ that senses nutrients, microbial products, inflammation and intestinal movement. In 2024, Signal Transduction and Targeted Therapy published a review of how the brain and the gut microbiome are connected through the immune, neural, neuroendocrine, and circulatory systems. In a 2021 randomized trial carried out at Stanford University, the authors found that a diet rich in fermented foods increased microbial diversity and lowered several markers of inflammation in the subjects, but did not find significant changes in reported stress or well-being. Modern research on gastrointestinal behavior has revealed it to be a highly complex bidirectional process in which the gut sends signals to the brain, via spinal and vagal visceral afferent pathways, and receives sympathetic and parasympathetic inputs. Multiple mechanisms exist whereby diet could modulate the gut-to-brain communication, including microbial-derived metabolites, hormonal, immune, metabolic, and neuronal pathways. I would compare this to a two-way communication line between the gut and the brain. Your gut and brain communicate through several pathways, including the vagus nerve. However, many clinical implications of microbiome-related signaling are still being studied. Indeed, controlled human trials testing many proposed microbiome-based treatments remain limited. The brain-gut axis has been the subject of research over the past several years. In addition, the enteric nervous system can help relay signals from the gut to the brain.

One major thing I point out to anyone learning about the gut-brain connection is that around 90% of our body's serotonin is made in our gut. I write about this in my upcoming book Wired to Thrive that is all about the gut-brain connection.

Gut health isn't just about digestion. It plays a major part in mood, brain function, and so much more throughout the body! Serotonin is what helps food move throughout the digestive tract, but it also plays a role in communication between the gut, nervous system, and immune system.

Take someone who is constipated. Many people who look at the gut as its own separate area in the body will typically associate poor mood with the pain that comes from constipation. If one truly learns the gut-brain connection, we can see that this connection is much deeper. That this change in gut function has effects on the nervous system and stress response. We can also turn this scenario around and see that things like stress and other situations that start in the brain could actually affect the gut microbiome and lead to the constipation.

I explain the gut-brain connection to my clients as a fire alarm. If one sensor senses a problem, the alarm will go off and then trigger the rest of the alarms throughout the entire house. The gut-brain connection works the same way. The system runs as a whole. If smoke is detected in the kitchen (or in this scenario, the gut), the alarm communicates with the rest of the alarms throughout the house. On the flip side, if smoke is detected in the living room (the brain), it does the same and communicates throughout the entire house.

I start with something they've already felt: butterflies before a big talk, or needing a bathroom when they're anxious. That's the gut-brain connection, and they've been living it all along. Then I describe it as a two-way phone line. The vagus nerve carries messages in both directions, so stress changes digestion, and an upset gut changes mood. For skeptics, the evidence that lands is IBS. Stress reliably makes symptoms flare, and gut-directed therapies like hypnotherapy improve symptoms in clinical trials. Once someone sees that calming the nervous system calms the gut, they stop hearing it as "it's all in your head." That's when they're willing to try the skills.

Rachel Harvest, MS, RDN, CDN, IFNCP Founder & CEO, The Harvest Method

As a science writer translating neuroscience into accessible concepts, the most effective analogy I use to bridge skepticism about the gut-brain axis is the "Subsea Fiber-Optic Cable."

Most people view the digestive tract merely as a mechanical food processor. To break that misconception, I explain that the Enteric Nervous System (ENS) contains over 100 million neurons—often termed "the second brain." The Vagus nerve acts as a massive bi-directional fiber-optic cable linking the brainstem directly to the gut.

The concrete evidence that always convinces skeptics is neurochemical: approximately 90% of the body's serotonin (the key neurotransmitter regulating mood and emotional tone) is synthesized in the gut by enterochromaffin cells, heavily influenced by microbial metabolism.

To make it intuitive, I point to universal bodily experiences: when someone experiences acute anticipatory anxiety, they feel immediate "butterflies" or gastrointestinal cramping. That isn't an imaginary feeling—it is the brain's sympathetic stress response instantly dialing down enteric blood flow and gut motility. Once people realize that their mood and gut share the exact same chemical messengers, the skepticism instantly vanishes.

Skeptical patients rarely need more science; they need to notice it in their own body first. I ask them when their stomach last tightened before a hard conversation, or when they lost their appetite during an exam week. Everyone has felt it. Then I explain that the gut and brain run on a two-way line, largely through the vagus nerve, so the traffic goes both ways: stress unsettles digestion, and a disturbed gut can colour mood and focus.

In my practice, one young professional insisted her afternoon anxiety had nothing to do with food. I asked her to keep a simple two-week log of meals, sleep and mood alongside her doctor's care. She spotted the pattern herself: her worst days followed short nights and lunches of only tea and biscuits.

Once people see their own data, the connection stops being a theory they have to believe.