Processed pet food is balanced so does not have excess salt and fat. Also heart attacks and high blood pressure are rare in cats so salt and fat are not usually a problem. Animals do not require changes in diet. If you want to change the diet, it is better to change slowly over a week or two, not quickly, If you wish to feed a variety of foods then feed a variety all the time so the animal is used to it. Cat foods are often made out of similar ingredients.
Most food made by name-brand manufacturers are of similar high quality.
Choose a cat food that says it is complete and balanced. Look on the back of the can and see if it has undergone feeding trials. Call the 1-800 number on the back or look at the manufacturers web site. Keep pet food as you would your own food. Keep it in a cool dry environment.