I think it's sad how contaminated our food supply has become with GMOs, chemicals, pollution. It's a wonder any of us are alive! Here's a link to a website that discusses renal failure in cats. Hopefully you will find it helpful.
http://avidlifepet.com/chronic-renal-failure-in-cats/
Thanks Opus. This article compelled me to look at the FF box. Of course there is corn and soy listed...