When a dog starts a new diet, the community of microbes in its gut changes. Wallflower bacteria multiply to dominate the scene, with the old guard slinking off in defeat. As microbial species jostle for control, their metabolic byproducts, many of which are critical for Fido’s overall health, change as well. The dynamic dance between nutrients, microbes, and their chemical products is well documented in dogs and other mammals, but until now, scientists were only guessing at the timeframe for microbial turnover. A new study documents the change takes place in less than a week.