The 29-year-old singer - who became the face of Weight Watchers in 2010 - feels like a "brand new" person since shedding the huge amount of weight.
She said: "Oh my god, yes, it`s a brand new me. Sometimes I don`t even recognise myself. I`ve lost 80 lbs."
However, she confirmed she didn`t want to get too slim, and is happy to stay at her current size.
She added to talk show host Oprah Winfrey: "That 4 and 2 and 0 is not for me."
The former `American Idol` star suffered family tragedy in 2008 when her brother Jason and mother Darnell were killed by her sister`s ex-husband and she admits she draws strength from her other relatives and 18-month-old son David Daniel - her child with her fiance, WWE wrestler David Otunga.
She said: "Well, my family. This is a very emotional subject. My baby. My grandmother. My mother. Even my brother I can hear him saying, `Jenny, knock it off,` like my mother right now would be saying to me, `Why you always crying, stop crying.`
"Their spirit was saying, `You`ve got to keep going.` And I try to do everything to say, `Will my mother like this? Will she be pleased? Will she be proud of that?`
"I don`t think I could ever come close to be the kind of mother that my mother was to me, but I try to use that as an example and be there for him the way she was there for me."