Gut biome actually changes pretty rapidly. IIRC some grad student did some kind of sequencing on his stool for a year, the the populations of different strains

Gut biome actually changes pretty rapidly. IIRC some grad student did some kind of sequencing on his stool for a year, the the populations of different strains of bacteria would completely flip when he ate a salad one day and a cheeseburger the next. His name was Lawrence David, but I can't quickly find the writeup that illustrates the point I'm making.