Diet modulates the gut microbiome, metabolism, and mammary gland inflammation to influence breast cancer risk.

Several studies have indicated a strong link between obesity and the risk of breast cancer. Obesity decreases gut microbial biodiversity and modulates Bacteroidetes-to-Firmicutes proportional abundance, suggesting that increased energy-harvesting capacity from indigestible dietary fibers and elevated lipopolysaccharide bioavailability may promote inflammation. To address the limited evidence linking diet-mediated changes in the gut microbiota to breast cancer risk, we aimed to determine how diet affects the microbiome and breast cancer risk. Female 3-week-old BALB/c mice were fed six different diets (control, high-sugar, lard, coconut oil, lard+flaxseed oil, and lard+safflower oil) for 10 weeks. Fecal 16s sequencing was performed for each group. Diet shifted fecal microbiome populations and modulated mammary gland macrophage infiltration. Fecal conditioned media shifted macrophage polarity and inflammation. In our DMBA-induced breast cancer model, diet differentially modulated tumor and mammary gland metabolism. We demonstrated how dietary patterns change metabolic outcomes, and gut microbiota, which may contribute to breast tumor risk. Furthermore, we showed the influence of diet on metabolism, inflammation, and macrophage polarity. This study suggests that dietary-microbiome interactions are key mediators of breast cancer risk.