Total misinformation! There are many people on the web and in pet stores who spread all this crazy stuff and have no idea what they are talking about.
BTW: rescue is not a way to make a living!!
Here is a great link about animal nutrition. There is a TON of free information there and it was founded by a highly qualified veterinary nutritionist. Her resume is on that site. There is a library with crazy amounts of information...but if you cannot find something, you can contact them with a question and they do answer!
https://www.petdiets.com/
ALSO....home cooking is great but you MUST use supplements and the diet MUST be properly balanced. This is another site that is great and also founded by a vet nutritionist:
https://secure.balanceit.com/ez/index.php?rotator=NewEz