Meat is mostly water. It is actual ash added to the food. This adds minerals to the food, but can cause crystals to form in the cat's kidneys. This sometimes ends in death.

I have found naturopathic veterinarians who recommend feeding cats raw, organic, cage free birds, bones and all. No house cat ever hunted and caught tuna or beef, or many other things we feed them.

Of the oldest domesticated cats, "Grandpa" Rex Allen, was fed bacon, eggs, steamed broccoli, and instant coffee. He was surpassed in age by another cat belonging to the same owner. He talks diet at 5:55.