I find it interesting because, from the little I've seen, most shows like this only talk about how fat is bad, and it's interesting to see that skinny isn't any better. Two of the 'superskinnys' stick out, in my mind. One was a nurse who lived on diet coke, and the other a single father who lived on chocolate. He was quite surprised to learn that his cholesterol was through the roof, since you generally assume that thin = healthy.
I also like the distinct lack of bitchiness. I keep expecting people to make snide remarks to each other,or whatever, and they just don't. I kind of like it.