Insulin is certainly important, but I really want to hear a convincing explanation for where those extra calories are going. The body doesn't just violate thermodynamics, digested calories go somewhere. You can gain weight even during ketogenesis, despite what the Atkins fanatics will tell you. Insulin isn't the only fat storage hormone, just one of the more powerful ones.
I lost 35 lbs in about 6 weeks at one point when I changed from one type of insulin to another (diabetic). My overall dose went down, and I wasn't having weird hunger surges from peaks in the insulin rates. I'm sure I was eating less, but simply having less insulin in my system made me store less fat.