I've heard that all cats are lactose intolerent but I could be wrong. Water is the best thing to give them. I do allow my Sunny to drink a very small amount of milk that is left over from my cereal though. I also give my cats the lactose free milk made especially for cats. There are catsip, laphappy, and whiskas brands.

Tuna fish is very bad for cats. It is high in polyunsaturated fat which cats have trouble metabolizing. Tuna can rob a cat's body of vitamin E, leading to a painful disease called steatitus, or Yellow Fat Disease, in which the skin becomes unbearably tender.

I got this information from one of my cat books.