Many biological processes exhibit daytime differences governed by rhythmic exposure to sunlight, termed circadian rhythms. Researchers recently found, in mice, that a protein critical to intestinal barrier function—helping the gut absorb nutrients while blocking harmful pathogens—is rhythmically controlled by nighttime liver metabolism of the molecule tryptophan. In this study, researchers found that when tryptophan—an amino acid needed to synthesize vital proteins—is ingested, it travels to the liver. There, tryptophan produces metabolites—molecular byproducts of metabolism—that activate a protein called the aryl hydrocarbon receptor (Ah receptor), which then works to improve barrier function in the gut. Gary Perdew, said that the findings...