This would be the pet-food industry speaking.  Cats should never have grain, starch or any type of sugar.  They must have no carbs, which turn to sugar.  Their bodies cannot process sugar, like ours can.  The result in cats is diabetes.  I had a cat with diabetes, and totally reversed it simply by doing research and learning these things.  Ever since, the cats that have been my companions have had normal blood-sugar levels.  Most of the diseases and conditions which domestic animals have today are the direct result of commercial food.  Cats in the wild don't suffer from the inflictions that are companions do, though they do have others.  But diabetes, kidney failure, and hyperthyroidism do not inflict cats in the wild, while these are the 3 top conditions of domestic cats.