One live mouse per day is the perfect diet for the domestic feline.
Petfood equivalent: 1/4-1/3 cup of dry food or one small can of wet food per day (the little cans - about 1/3 the size of a can of tuna). Obviously, ensure an unlimited supply of clean fresh water as well. Milk and dairy should not be fed to adult cats.
Ensure the food is of high quality or the cat will develop digestive/metabolism problems as it ages... look for a low ash content in dry food, and look for real meat in wet food. Brand names like "Science Diet" and the like are the way to go, stay away from Purina... their feeds are OK for an animal you are going to eat but are substandard for a long healthy life for a pet.
I realise most cats will react badly to this amount of food if previously overfed, they will chew your ankles off for a few weeks but will eventually adjust.