I am in my second week on the Alternate plan. I started IP in late March, and though I was losing weight consistantly, I felt terrible. Was never able to get past feeling dizzy and had really low energy. These problems combined with the fact that at the end of June I'll be going to Hawaii for 3 weeks where I'll be very active every day, compelled me to switch. I didn't want to go off plan while on vacation, but would never be able to keep up with my family if I wasn't getting more food.
My weigh-in last week had me down 1 lb and 1.5 inches. My initial reaction was disappointment, but I've gotten past by reminding myself that having a way to steadily lose weight and learning to be healthy trumps instant fix.