Updated project metadata. Diet plays a major role in altering the composition and function of the gut microbiota. Previously most studies have focused on the effects of fiber, fat, and different amounts of protein on the gut microbiota. In this study we investigated how different sources of protein affect the gut microbiota of mice. We fed conventional and germ-free C57BL/6J mice a series of defined diets where the source of dietary protein was the key difference, which made up twenty or forty percent of the diet. The dietary protein sources used were purified protein. The diets were fed to the same mice for one week each with a fecal sample collected at the end of each week. The diets were fed in this order: standard chow, 20% soy, 20% casein, 20% rice, 40% soy, 20% yeast, 40% casein, 20% pea, 20% egg white protein, 20% chicken bone broth, and lastly at the end of the experiment half of the mice were fed the 20% soy and half the mice the 20% casein diet again as a control. We did not collect fecal samples for the chicken bone broth diet as the diet was stopped prematurely due to diet intolerance. 12 germ-free mice (6 female, 6 male) in four cages were used. 12 mice with a conventional gut microbiota in four cages were used (6 female, 6 male). One germ-free mouse was found dead after diet 5 (20% yeast) and one conventional mouse was sacrificed after the second diet (20% casein). No sample could be collected from one of the conventional mice after the 20% egg white diet.