Cats originated in the desert and have evolved to obtain water requirements almost entirely from the moisture content in food. Canned diets contain enough water that cats consuming them rarely need to drink. Thus the cat needs to drink less than 1 oz. of additional water per day whereas a cat consuming a dry diet needs to drink over 7 oz. of water per day. This can be difficult because cats are not naturally big drinkers and frequently leads to bladder and kidney problems.
Cats, being true carnivores, must have meat in the diet. Cats require 20 amino acids to make all the needed body proteins. Ten can be created in the liver and need not be present in the diet. The other 10 amino acids are essential amino acids and cannot be made by the liver. They must be supplied by meat in the diet.
Cats have no absolute carbohydrate requirement. Carnivores convert glucogenic amino acids and glycerol to glucose for the maintenance of blood glucose. In general, an absence of dietary carbohydrate in the feline diet will not affect blood glucose levels or cause an energy deficiency; this is because the body can use protein and the glycerol portion of fat for glucose production, and fat and protein for energy.