It takes up to 24 hours to change the balance of power in your gut. Switching to a diet based exclusively on animals or plants triggers rapid changes to the microbes that rule your gut. The human body contains a community of other organisms known as microbiome, these microbial cells outnumber our own by 10 to 1, with most of them colonising the gut. Peter Turnbaugh at Harvard University and his colleagues investigated changes in diet and its effect on microbes in the gut. In the case of the animal-based diet, they saw an increase of the bacterium Bilophila wadsworthia, which aids the digestion of saturated fats in milk. However, an increase of these bacteria has been linked to inflammatory bowel disease in mice. Switching to a plant-based diet prompted a hike in the numbers of bacteria that produce a fatty acid called butyrate, which seems to reduce inflammation. Harry Flint at the University of Aberdeen, Uk says that butyrate is thought to reduce colorectal cancer risk by boosting the health of cells lining the intestines and prompting cancerous cells to self-destruct. Interestingly, the changes to the gut microbiomes were short-lived since they reverted to the original structure about two days after people went back to their normal diet.