During a visit Wednesday to a shore town devastated by Superstorm Sandy, Christie was asked about the doctor's comments.
Unless Mariano gives him a physical exam and learns his family history, "she should shut up," the Republican governor said.
Christie said his children heard the doctor's comments and his preteen son asked him if he was going to die.
"This is just another hack who wants five minutes on TV," Christie said.
He has never revealed his weight, but he has repeatedly said keeping it in check has been a longtime struggle.
Christie joked about his size during an appearance Monday on "The Late Show with David Letterman," pulling out a doughnut and saying his girth is "fair game" for comedians.
The next day, he spoke frankly about his efforts to lose weight and described himself as "remarkably healthy," but he also acknowledged his doctor "continues to warn me that my luck is going to run out relatively soon."
Christie, often mentioned as a possible presidential candidate, has never released his medical records. He had one health scare during his first term, an asthma attack in the summer of 2011 that sent him to a hospital but did not require him to be admitted. He blamed it on the heat, not his weight.