'Biggest Loser' Winner: Don't Go Suing If You Get Fat Again

"The Biggest Loser" is under fire by former contestants, but a past champion says the woman blaming the show for regaining tons of weight needs to take a look in the mirror.

Ali Vincent won 'BL' season 5 -- and recently gained all her pre-show weight back.

But unlike Suzanne Mendonca and others, Ali says her weight gain was her own fault and she's working hard on her own to get it off.

As for the class action lawsuit Mendonca says she's filing ... Ali calls it "preposterous." She had other choice words for 'BL' haters.