Problem:

Here's the reason why I'm asking: I've heard that it takes some time for pets(cats/dogs) to adjust to a different dry feed, where the new feed has to be mixed with the old one, slowly replacing the old one. I'm wondering if this advice has any truth in it, and if so, does this apply to humans as well?

For example, a cat eats the same kind of food for months at a time, but humans vary their diet much more dramatically. Are there any benefits to eating the same kind of food over extended period of time? I'm interested in knowing if the digestive system/symbiotic bacteria in the gut adapts to the food, resulting in better digestion/absorption of nutrients.

Please suggest some ideas.