First of all, where did 당신 read that? I have never read 또는 seen that the boys were forced to lose weight and if they do that, i suppose its their management who is 더 많이 concerned about their image than their music.
Secondly, they will NEVER end up like Michael Jackson because they arent (no offence to the 팬 of the king of pop) crazy dark skin people who think being white is going to stop criticism and racism. Sorry again to the 팬 but thats my opinion :(
Again, the boys are healthy and im quite sure if they exercise is for their own good