Driven by the pleasurable experience of sweet taste, over the past two centuries, per capita consumption of dietary fructose has increased 100-fold. Excessive fructose consumption contributes to metabolic diseases, including obesity, diabetes and fatty liver disease. Unlike glucose, high-dose fructose is not fully absorbed by the small intestine and excess fructose spills over to the colon, feeding gut microbiota. Remarkably, antibiotics treatment in rodents prevents fructose-induced pathologies, indicating key roles of microbiota in the disease development. In this study, we will determine how chronic fructose feeding progressively alters microbiota, host metabolism and immune system, contributing to fatty liver disease. We will perform metabolomics, metagenome sequencing and physiological analysis in our new genetic mouse model that shows increased fructose spillover to the colon and worsened fatty liver upon fructose feeding. The study will reveal the causal relationship between microbiota and fructose-elicited pathologies, thereby elucidating the underlying mechanisms of the disease.