oh my, that's scary! The guy is a complete quack!Read this.
http://www.citypages.com/2011-07-20/news/eric-weisman-won-t-stop-playing-doctor/
This is the creator of the food.
If link won't work just google "evolution vegan cat" it comes up as one of first few hits.
I would be checking your cats blood sugar at home. Ask the vet to show you how.