High-Fat Diets: Gut Bacteria May Enter Brain & Impact Neurological Health

Live bacteria from the gut can travel to the brain via the vagus nerve, according to a new study from Emory University, potentially influencing neurological health.

The gut, with its more than 100 million neurons, has long been recognized for its connection to overall well-being, a concept rooted in ancient traditions across cultures like Greece, Japan, China, and India. The Emory University study, published in PLOS Biology in March, provides a biological mechanism for this gut-brain connection.

Researchers found that a high-fat diet can compromise the intestinal barrier, leading to increased permeability – often referred to as “leaky gut” – allowing live bacteria to migrate from the gut to the brain. This journey occurs through the vagus nerve, a critical pathway connecting the brainstem to major organs including the heart, lungs, stomach, and intestines.

“One of the biggest translational aspects of this study is that it suggests that the development of neurological conditions may be initiated in the gut,” said David Weiss, co-principal investigator of the study and a microbiologist at Emory University’s School of Medicine.

The study utilized germ-free mice fed a diet high in fat (35%) and carbohydrates (45%), mirroring a typical Western diet. This dietary regimen induced changes in the gut microbiome and increased intestinal permeability. To confirm the bacterial translocation, researchers administered antibiotics to reduce the gut microbe population, then introduced a genetically engineered strain of Enterobacter cloacae. The engineered bacterium, containing a unique DNA barcode, was subsequently detected in the vagus nerve and brain of mice consuming the high-fat diet.

Researchers emphasized the rigor of their methodology, stating that stringent measures were taken to prevent contamination and that the bacterial loads found in the brains were low – in the hundreds – ruling out systemic infection like sepsis or meningitis.

The study also revealed low levels of bacteria in the brains of mouse models exhibiting neurological conditions such as Parkinson’s and Alzheimer’s disease, suggesting a potential link between gut microbiome imbalances and the onset of these conditions in humans.

“This research highlights the require for further study into how dietary shifts have a huge influence on human behavior and neurological health,” said Arash Grakoui, co-principal investigator of the study and professor of medicine, microbiology, and immunology at Emory University.

Notably, the researchers found that returning the mice to a normal diet reduced gut permeability and decreased the bacterial load in the brain, indicating that the effects of a high-fat diet on bacterial translocation may be reversible.