"Poker Face" Reveals Lady Gaga's Food, Weight, Psychological Issues

Sept. 8, 2010— -- Lady Gaga's career may be in the stratosphere but a new unauthorized biography reveals that her breathless journey to the top was not a smooth trajectory.

In "Poker Face: The Rise and Rise of Lady Gaga," which comes out September 14, author Maureen Callahan discloses that Lady Gaga -- one of the world's most image-conscious pop stars -- has weathered her share of weight, food and psychological issues.

"We haven't seen a character like this since Madonna and Prince, and Gaga has done [her career] so much faster and exploded in a bigger way," Callahan, a reporter at the New York Post, told ABCNews.com. The author opted to write the book independently, without her subject's involvement, so that she could freely approach whomever she wanted for information. She has never interviewed Lady Gaga.

It was Lady Gaga's uniqueness -- Callahan calls her "quick-witted, defiant and funny" and the fact that she has not made many career missteps -- that drew the author to her subject.

"The book shows Lady Gaga is more different than you ever thought," she said. "To me, she's one of the biggest contradictions, ever."

Callahan said Lady Gaga's poor eating habits seem to have begun when she signed with Rob Fusari, her first producer.

"It was made clear to her by her people that she needed to have a certain look," said Callahan.

One source mentioned that the artist often fumed while seeking a record deal because people weren't looking at her.

The game changer, said Callahan, was when Lady Gaga began doing photo shoots. A month before a key shoot, she dropped 20 pounds.

"All pop stars get this pressure put on them," says Callahan.Maureen Callahan's "Poker Face."