Can Your Gut Affect Anxiety and Depression? UCLA Expert Explains the Gut-Brain Connection

In an interview with The Educated Patient, Tiffany Ho, Ph.D., says growing research into the “gut-brain axis” is changing the way scientists understand mental health, inflammation and overall well-being. According to Ho, an associate professor of clinical psychology at UCLA Health, the gut and brain are constantly communicating through several biological pathways that may influence mood, anxiety, stress and even cognitive symptoms like brain fog.

One of the most important communication systems is the vagus nerve, which connects the brainstem to organs throughout the body, including the stomach and intestines. Ho explained that roughly 80% of the signals carried by the vagus nerve travel from the gut to the brain, highlighting just how influential gut activity may be on brain function. These signals help the brain monitor things like food intake, hormone levels, inflammation and chemical activity from gut bacteria.

Another major pathway involves the immune system. Ho noted that approximately 70% of the body’s immune cells are located in the gut lining. When gut bacteria become imbalanced, this can trigger low-grade inflammation that may eventually become chronic. Research increasingly suggests that chronic inflammation is linked to depression, anxiety and other health conditions.

Ho also discussed the role of the microbiome, which includes not only the microorganisms living in the gut but also the compounds they produce and the surrounding environment. These microbial compounds, known as metabolites, can influence the integrity of the gut lining and the blood-brain barrier — the protective system that helps shield the brain from harmful substances. When both barriers become compromised, inflammation may spread more easily throughout the body and potentially affect brain function.

Importantly, Ho emphasized that the microbiome itself is not a “barrier” to emotional health, but rather a “bridge” that helps researchers understand how the gut and brain interact.

The conversation also touched on neurotransmitters such as serotonin, which is closely tied to mood regulation. While many people associate serotonin with the brain, Ho explained that about 90% of serotonin receptors are actually found in the gut. Although serotonin itself cannot cross into the brain, gut microbes may still indirectly affect brain chemistry by influencing amino acids like tryptophan, which help the brain produce serotonin.

Ho stressed that scientists are still learning about the gut-brain connection, but the research continues to reveal how deeply interconnected physical and mental health truly are.