The only reality show we watch is the Biggest Loser so I suppose one could say that it's all plus sized people. I think they are treated with respect and encouraged to feel happy at whatever size they are at.
That being said, the thrust of the show is to lose weight, so while the mentors are enthusiastic about everyone being happy "now", the participants are also going in with the mindset that they want to be a lighter weight.
Most of them are doing it for serious health reasons, though, not to "look prettier". A good portion of them are facing high risk of serious medical complications or death by the time they get to the show.