Dr. Connie Mariano, a career Navy doctor who headed the White House Medical Unit under President Bill Clinton, told CNN after Christie's appearance Monday on "The David Letterman Show" he might die in office if he was elected president.
An angry Christie, speaking at a news conference in Sea Girt, N.J., said his four children saw her on TV. He also said Mariano has never examined him.
"This is just another hack who wants five minutes on TV," he said.
Mariano said she was trying to be "constructive."
"But when I see someone who looks like him, you don't have to be a White House doctor to be concerned about health issues," she told CNN.
Christie in a news conference Monday acknowledged his weight is a problem and that his doctor had warned him his luck might soon run out. On Letterman, however, he joked about it, calling himself "the healthiest fat guy you've ever seen in your life."