No rice diet

Hi, Jus wondering completely avoiding taking rice ( carbo ) will harm the baby or not? My sis who is pregnant now skip taking rice every meal. She said doc told her not to take carbo...lol. thats insane right?! She is into her last mth pregnancy now, but she still doesnt wan to take any rice plus she is avoiding eating alot, evrytime saw her eat small bowl of vege and meat only & she has been skipping rice intake since the day she's pregnant. She's healthy , no high blood pressure, why she is doing this, i totally confuse... I jus wan to understand whats the logic behind for not taking rice? So that can slim back faster? #advicepls