No. We prefer to make the switch immediately. Bring the new food home if they like it, take away the old food and monitor your pet to make sure they are eating. What goes in must come out, so also watch the litter box.
If a new food tastes good you can convince them to try it, but if you continue to mix the old with the new they often revert back to the old. Why? Because the novelty wears off and the old food is a safer bet. Cats do not handle change well and a new food represents a new threat. Once a cat is eating a new food they will continue to do so as long as you do not give them another option. It takes about two weeks for a cat to develop a new habit, including the total acceptance of a new food.
In our experience as long as you go from a lower quality food to a higher quality food, you can just switch your cat over with few if any issues. A higher quality food is usually defined as having a higher percentage of animal protein and fat and less than 6% starch/carbs. Because Young Again Cat Food is such a high energy diet, it is not uncommon to have soft stool the consistency of mashed potatoes for a few days to two weeks. This is normal and not harmful in any way. It takes your cat a little time to learn that our food is nutrient dense and they don't need to eat as much. As soon as you see firm stool all is good.
If at any time you have questions please email or call us, we actually have live people answering the phone and we monitor emails after hours and on weekends.