Fecal microbiota transplantation from mice with circadian disruption into germ-free mice induces glucose intolerance, increased adiposity, and hepatic steatosis, demonstrating that a dysregulated, arrhythmic gut microbiome is sufficient to drive metabolic dysfunction independent of host circadian genotype.

When gut bacteria lose their daily rhythm, they stop producing key chemicals at the right times. This causes the gut lining to become leaky, allowing bacterial toxins to enter the bloodstream. These toxins trigger chronic inflammation in the liver and fat tissue, which blocks insulin from working properly. At the same time, the liver can't regulate blood sugar or fat storage correctly because the signals from bile acids and immune molecules are out of sync. The result is high blood sugar, excess fat in the liver, and weight gain.