The cliché “you are what you eat” has been used for hundreds of years to illustrate the link between diet and health. Now, an international team of researchers has found the molecular proof of this concept, demonstrating how diet ultimately affects immunity through the gut microbiome.

The team’s work, conducted in mice, reveals that what animals consume initiates the release of a metabolic byproduct from a specific gut microbe that, in turn, modulates the animals’ gut immunity.

he findings, published Nov. 10 in Nature, offer a unifying explanation for the complex interplay between diet, gut microbiota, and immune function. They are the result of collaboration among scientists at Harvard Medical School, Brigham and Women’s Hospital, Seoul National University, and Monash University in Australia.

The experiments pinpoint a microbial molecule, the synthesis and release of which are influenced by host diet. That molecule, in turn, stimulates the activation and signaling of a subset of cells known as natural killer (NK) T cells, which are involved in immune regulation and implicated in a range of inflammatory conditions.