Jennifer Hudson's sexy new body: How much did she lose? (PICTURES)

(CBS) Is Jennifer Hudson too thin?

That's what some were wondering last night when the formerly full-figured singer - and Weight Watchers pitchman - walked on stage to present an award at the Academy Awards ceremony.

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Just how much weight has Hudson lost? Thirty pounds? Forty?

Actually, it's twice that.

"I've lost 80 pounds," she said in a recent appearance on the Oprah Winfrey Show, falling from a size 16 to a size six. Having given birth to a boy more than a year ago, she told Oprah, "I wanted my body back. I always say if you don't like something, change it."

But is the dramatic weight loss sustainable? Is it healthy? Dietitians aren't so sure.

"Jennifer Hudson's appearance left me wondering how far she has pushed the Weight Watchers diet," New York City-based dietitian Marisa Sherry tells CBS News. "She looks good, but each time I see her she seems to be getting skinnier and skinnier and she's now at the point where I would start to question how far she will go."

Hudson herself says she's happy where she is, and has no plans to lose more weight.

"I like meat on my bones now," she told Oprah. "That four and that two and that zero is not for me."