3 o'clock in the morning and I'm reading my cat...

3 o'clock in the morning and I'm reading my cat book I got at a yard sale for 10 cents. It's pretty good. I especially enjoyed the part about their tails and how they use them as communication devices.

Anyway, I got to the part about diet and the book says you shouldn't change their food too often as this might cause digestive problems. I change up my kitty's food all the time and have seen no problems. She has a variety of flavors of wet catfood in the morning and two flavors of dry which I alternate in the evening. The book says "Don't worry about feeding your cat the same thing all the time. Variety doesn't matter to cats."

My question: how the hell does this guy know?