Cat food is probably OK as human food. Probably nearly all cat food is human grade cat food. The ingredients are acceptable. Although "by products" in cat food is material that is not fit for human consumption; that said as I understand it, it is cooked at a sufficiently high temperature to kill bacteria (hence the ash in cat food).
I am sure there are many cases of humans living off cat or dog food mostly I suspect for short periods of time (I hope!). In some ways dry cat food is more suited to humans with its high carbohydrate content. There is a gradual realization that dry cat food is not wholly suitable for cats, which seems a strange thing to say. But it should be realized that cat food is a commercial product and in order to please company shareholders the first duty of a company is to make a profit, the second duty is to feed cats well.
There is a company executive whose job in part is to manage the pet food quality at Marks and Spencers. He eats it to check it. There again M&S cat food is very high quality and probably resembles a paté or paste that could be spread onto toast. In short it is definitely human grade cat food.
So that's decided humans can eat cat food but cats can't eat dog food and dogs can but shouldn't eat cat food even if they prefer it as the dietary requirements are different. The cat is an obligate carnivore (must eat flesh) although this does not seem to be respected by the cat food manufacturers. Dogs are also carnivores as far as I aware but are more flexible in their dietary requirements.
On a more serious note, a 2 year old child living in California was found to have lived off dry cat food for 6 days because his mother had sadly died. This shows great resourcefulness for a young child.
Note: The taste of dry cat food is bland, much like a dry biscuit but not distasteful. It is not too hard and there is a lingering taste in the mouth (I've just tried some that's how I know!).
Human grade cat food to cat food recipe
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