Gut dysbiosis induced by sunflower oil-based sucrose-free high-fat diet leads to steatohepatitis.

High-fat diets (HFDs) are known to disrupt gut microbiota, contributing to obesity, inflammation, and metabolic disorders. Although sucrose is a known driver of gut dysbiosis, the microbiome alterations caused by sucrose-free fish oil and sunflower oil-based HFDs remain unclear. To investigate how sucrose-free sunflower oil-based (S-HFD) and fish oil-based (F-HFD) high-fat diets influence gut microbiota composition, metabolic health, and liver inflammation in mice. C57BL/6 mice were fed either S-HFD or F-HFD for 24 weeks. Body weight, insulin sensitivity, liver inflammation, and gene expression were assessed. Gut microbiota composition was analyzed using 16S rRNA sequencing, followed by diversity analysis and taxonomic profiling with Microbiome Analyst and MIAOME tools. Despite similar body weights between groups, the gut microbiota composition differed significantly. The S-HFD group showed a higher abundance of Firmicutes (40%) compared to the F-HFD group (3%), while Verrucomicrobia were dominant in F-HFD (26%) and nearly absent in S-HFD. Taxa such as RF39, Christensenellaceae, Mogibacteriaceae, and Yaniella were enriched in S-HFD mice and associated with metabolic and immune dysregulation. S-HFD mice also had elevated fasting glucose, increased hepatic monocyte/macrophage (F4/80+) infiltration, macrovesicular steatosis, lobular inflammation, and upregulation of genes related to fatty acid oxidation (Cpt1a), monocyte chemotaxis (Ccl2), lipogenesis (Scd1, Fasn, Acaca), and glycolysis (Pklr). Conversely, F-HFD mice showed increased expression of the insulin-sensitive gene FATP1. Sucrose-free sunflower oil- and fish oil-based high-fat diets induce distinct gut microbiota changes and metabolic responses. S-HFD is associated with gut dysbiosis and steatohepatitis-like features, highlighting the importance of fat sources in shaping microbiome-host interactions in metabolic disease.