Diets high in fat affect genes linked to immune system and brain function, and increase susceptibility to Covid-19. A study conducted at the University of California - Riverside fed mice high-fat diets for 24 weeks and found concerning changes in gene expression. The diets included saturated fat from coconut oil, monounsaturated and modified soybean oil, and unmodified soybean oil high in polyunsaturated fat. These diets not only impair immune system genes but also create an environment for harmful gut bacteria to thrive.