When did Lisa Whelchel (Blair) get fat? I certainly don't remember and I met her in 2005 at a homeschool conference (at which she was the guest speaker) in Orlando.
She was still gorgeous!! Incidentally, someone mentioned the whole virginity thing and the TV show. According to Whelchel, the writers originally wanted to have Blair lose her virginity. But Whelchel refused to do the part. And since she was the major cog of the show, they changed the script to have Natalie be the one who got de-flowered, so to speak.
As for Kim Fields ("Tootie"), the problem for her on the show was the suits were trying to keep her in the sweet, cute, little girl role....while her breasts were getting bigger than her head. Hence, they kept having her wear oversized clothes. But, after a while, even that didn't help.