Wet food

Canned or wet food generally comes in common can sizes of 3 oz (85 gm), 5.5 oz, and 13 oz. It is also sold in foil pouch form by some manufacturers.
Owners and veterinarians who recommend a diet

consisting largely or entirely of canned, homemade or raw cat food point to higher water content of such food and the increased total water consumption in comparison to a dry food diet as an important health benefit.[citation needed] Wet food also generally contains significantly less grain and other carbohydrate material, although many are made with fish ingredients.

Canned cat foods in pop-top containers may play a role in the development of hyperthyroidism in cats. This may be due to bisphenol A used in the pop-top can coating leaching into the food.Some cat foods also contain goitrogens, such as soybean products.

In general, canned, homemade, or raw foods are thought to either help treat or noticeably reduce the likelihood of numerous health issues including urinary tract disorders, diabetes, chronic renal failure, constipation (sometimes leading to megacolon), and obesity.

Source : http://en.wikipedia.org/wiki/Cat_food