Some people really do lose *while eating nutrisystem food*, mainly because the portions are so small and I've heard some of the food is horrible and many can't bring themselves to even eat it. The biggest problem is that when you stop purchasing their food, you will gain all of your weight back.
I've lost 38 lbs. by low carbing, I started with South Beach and tweaked my diet for my own needs. I don't eat all the grain that SB allows. I eat lots of whole foods, meat, fish, poultry, eggs, vegetables, sweet potatoes, occassional brown rice, and even some oatmeal about once a week. The weight is still coming off and I eat plenty of food, certainly not hungry with it.
The reason they work, is that you are pretty regimented in what you can eat. Anyone can lose weight if they eat that little.
The last time I looked at Nutrisystem, it was upwards of $300+ a month for the food. Yikes!