Researchers Find High-Fat Diets May Let Gut Bacteria Reach Brain

A new study published in PLOS Biology suggests that bacteria from the gut may directly reach the brain, revealing a surprising mechanism behind the gut–brain connection. The research, conducted by scientists at Emory University, indicates that imbalances in the gut microbiome could influence neurological health.

The digestive system contains more than 100 million neurons, which is why it is often referred to as the body’s “second brain.” Researchers have long suspected that the gut and brain communicate closely, but the new study provides evidence that live bacteria may physically travel from the gut to the brain.

Using mouse models, the scientists discovered that bacteria from an imbalanced microbiome could move along the Vagus Nerve, a major nerve that connects the brainstem with organs such as the stomach, intestines, heart, and lungs. The team observed that this pathway allowed microbes to reach the brain without appearing in the bloodstream or other organs.

To test this process, researchers fed germ-free mice a high-fat diet known as Paigen's Diet, which resembles a typical Western diet. This diet increased intestinal permeability, often referred to as “leaky gut,” allowing substances to escape the intestine more easily.

Scientists then introduced a specially engineered strain of Enterobacter cloacae containing a unique DNA barcode. After the mice consumed the high-fat diet, the same bacterial strain was detected in both the vagus nerve and the brain.

Importantly, the bacterial levels found in the brain were very low, ruling out severe infections such as Meningitis or sepsis. Researchers also identified small amounts of bacteria in mouse models of Parkinson's Disease and Alzheimer's Disease.

The findings suggest that neurological diseases may sometimes originate in the gut. Encouragingly, when mice were returned to a normal diet, bacterial levels in the brain decreased, indicating that dietary changes might help restore gut and brain health.

REFERENCE: Thapa, M., et al. (2026) Translocation of bacteria from the gut to the brain in mice. PLOS Biology. DOI: 10.1371/journal.pbio.3003652. https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3003652