NEW YORK (Reuters) - New Jersey Governor Chris Christie responded angrily on Wednesday to a former White House physician's comment that he could die in office if he does not lose weight, calling the doctor a "hack" for offering advice without examining him.

Connie Mariano, a doctor in the White House medical unit from 1992 to 2001, said in an interview on CNN that Christie, a blunt-spoken Republican who is seen as a strong contender if he decides to run for president in 2016, risks a heart attack or a stroke if he does not slim down.

"It's almost like a time bomb waiting to happen unless he addresses those issues before running for office," Mariano said.

Asked about the comments on Wednesday, Christie, who has spoken openly about his struggle to lose weight, said Mariano was out of line.

"I find it fascinating that a doctor in Arizona who has never met me, never examined me, never reviewed my medical history or records, knows nothing about my family history, could make a diagnosis from 2,400 miles away. She must be a genius," Christie said, adding: "My children saw that."

He called Mariano "just another hack who wants five minutes on TV."

Mariano's comments came after Christie appeared on the Late Show with David Letterman and poked fun at his own size - producing a donut while Letterman was mid-joke.

"I'm basically the healthiest fat guy you've ever seen in your life," Christie said.

But Mariano, who helped former President Bill Clinton during his White House years, said her advice was not partisan.

"I'm a Republican. I like Chris Christie. I want him to run. I just want him to lose weight," Mariano said. "I'm a physician more than I'm a Democrat or Republican. And I'm worried about this man dying in office."

In a follow-up interview on CNN on Wednesday, Mariano said she and Christie had spoken by phone.

"The words gracious and appreciative don't come to mind," she said, adding that Christie had asked her not to share the specifics of their conversation.

"You don't have to be a doctor to look at him and see that he has a problem with weight," she said. "I have patients who suffer with obesity, and it is not a laughing matter."