People who eat plenty of protein and animal fats have predominantly Bacteroides bacteria in their guts, whereas in the intestines of those who consume more carbohydrates Prevotella species dominate.

Gary Wu at the University of Pennsylvania in Philadelphia and his colleagues recorded the dietary habits of 98 healthy people and catalogued their gut microbiomes by sequencing a specific stretch of bacterial DNA that can be used to identify and classify bacterial species. Putting ten individuals on a controlled diet for ten days did not alter their dominant gut bacteria, despite minor species changes occurring within the first 24 hours. This suggests that long-term diet is strongly associated with gut-microbiome composition.

The authors think that long-term dietary changes might aid in the treatment of conditions such as obesity and diabetes, which may be linked to the balance of gut bacteria.

Science 10.1126/science.1208344 (2011)