I haven't heard of "Power Plan", however, it sounds similar to "ZonePerfect". The only prob is, the porton of foods you consume is fairly small, and it requires that you eat every 4 hours in order to stay in the zone. (nothing in between). Their products, in my opion are pretty satisfying, especially the bars and shakes. Check out their website, www.***************.
I actually did pretty good on the zone (lost 6 lbs. and also did "Winsdor Pilates") for only week. I got tired of working out (ha ha ha). So its harder to lose if you dont workout. But still on the zone. Give it a try.