Fish Oil vs. Sunflower Oil: How Fat Source Shapes Gut Bacteria and Liver Health in Mice

This mouse study compared two high-fat diets that contained no added sucrose: one based on sunflower oil (rich in omega-6 fats) and one based on fish oil (rich in omega-3 fats). Mice were fed these diets for 24 weeks, and researchers looked at gut bacteria, blood sugar control, and liver tissue changes.

Even though both groups of mice ended up with similar body weights, their gut microbiomes looked very different. The sunflower oil group had a much higher proportion of Firmicutes bacteria and almost no Verrucomicrobia, while the fish oil group showed the opposite pattern. Certain bacterial groups enriched in the sunflower oil mice have been linked in other research to immune and metabolic disruption.

The sunflower oil group also had higher fasting blood glucose, more immune cell infiltration in the liver, fatty liver changes (macrovesicular steatosis), and signs of liver inflammation. Genes involved in fat storage, sugar breakdown, and inflammatory signaling were turned up in their livers. In contrast, the fish oil group showed higher activity of a gene linked to healthy insulin response and fat transport.