By Debbie Emery - Breaking Celebrity News Reporter

After stepping out in a gaping cardigan with her sunken chest, jutting ribs and gaunt face clearly on show, Selma Blair has shocked both fans and health professionals with her dramatic weight loss.

"She looks extremely malnourished and at 5'3" can only weigh 75 to 80 pounds," nutritionist and The Hamptons Diet author, Dr. Fred Pescatore, who has not treated the star, told Breaking Celebrity News in an exclusive interview.

As we previously reported, Blair, 40, and fashion designer Jason Bleick, 42, broke up in September after reportedly "fighting non-stop" and have since strived hard to be amicable for the sake of their 16-month-old son, Arthur, but the stress has made her a shadow of her former bubbly, healthy looking self.

"I'd say she's definitely a thin person now, and does look gaunt and sunken-in," Jackie Keller, CEO of NutriFit and author of Body After Baby exclusively revealed to Breaking Celebrity News, explaining how heartbreak can have a devastating affect on someone's eating habits.