Growth rate will be dependant on:
-More food
-Feeder Types
-Supplementation
-UV Exposure
-Health of chameleon
-Health of feeder
-Gutload
-Bloodline
-Parasites
-Species/subspecies
As for your question aout fat, it really depends how much fat the chameleon absorbes from the feeders, and how much "excercise" they do.