U.S. Department of Health and Human Services

Diet High in Milk Fat May Promote Harmful Intestinal Bacteria and Inflammation

Scientists have shown that mice with a pre-existing genetic susceptibility to intestinal inflammation fed a diet high in saturated fats from milk have altered intestinal microbial communities that occur along with changes in bile acid composition, altered immune function, and increased intestinal inflammation. Inflammatory bowel diseases (IBD), including Crohn’s disease and ulcerative colitis, are thought to result from a complex interplay between genetic and environmental factors. The rising incidence of these conditions in recent decades, together with studies showing increases in IBD in immigrants relocating from low-prevalence to high-prevalence countries and their children, point to a growing influence of environmental factors, such as diet. The dynamic communities of intestinal microbes, which are profoundly interdependent with humans in terms of metabolizing dietary nutrients, have received more attention in recent years for their potential contributions to human health and diseases such as IBD. In this study, scientists fed mice for 3 weeks on a diet high in fat—either milk fats, lard, or safflower oil from plants—which mimicked the fat levels found in Western diets, and compared them to mice fed a low-fat diet. They first looked to see the effect of these diets on the types and abundances of microbes present in the stool using genetic sequencing. All of the high-fat diets reduced the diversity of microbes present compared to the low-fat diet. In mice fed the high milk-fat diet, the scientists observed a “bloom” or explosion in the number of a particular bacterium, called Bilophila wadsworthia—a bacterium often detected in illnesses such as appendicitis and other types of intestinal inflammation. The researchers also examined mice with a genetic susceptibility to develop intestinal inflammation (colitis) due to deficiency of the gene encoding Il10, which is part of the immune system. These mice showed increased colitis when fed a milk fat diet compared to the susceptible mice fed diets high in fats from plants or low in fat, or compared to mice without the genetic risk that were fed the high milk-fat diet. The genetically susceptible mice fed high milk-fat also had altered immune functions and more abundant levels of B. wadsworthia and taurocholic acid, a form of bile acid in which these bacteria thrive. Of note, the byproducts of bacterial metabolism of these bile acids and other substrates can injure and breach the inner protective barrier of the gut, leading to inflammation and damage. This pioneering work in mice connects the dots between genetics, the immune system, diet, and microbes to outline a compelling picture of how these factors may be interacting in the development of human intestinal inflammatory conditions such as IBD. While these findings require replication in humans, they offer a glimpse into the future of how these diseases might be treated or prevented in susceptible individuals through dietary and/or microbial means.

Devkota S, Wang Y, Musch MW, et al. Dietary-fat-induced taurocholic acid promotes pathobiont expansion and colitis in Il10-/- mice. Nature 487: 104-108, 2012.