NEWARK, N.J. - Answering questions about weight-loss surgery he had kept secret for 12 weeks, Gov. Christie on Tuesday rejected a political motivation but squelched most other inquiries about the details.

He declined to say how much he weighs now and how much weight he has lost. It's none of anyone's business, he said.

He conceded he used an alias at the hospital, but declined to say what it was.

"I turned 50 years old, and it made me think - [you get] confronted with your own mortality as you start to age," Christie said. "So from my perspective this is about [my wife] Mary Pat, and the kids, and me, and it's really not about anyone else."

The nation learned that the famously rotund Republican governor - whose weight, never officially revealed, has been a source of pundits' fascination and comedians' derision - is steadily eating less and losing weight after secretly undergoing outpatient laparoscopic adjustable-gastric-band surgery Feb. 16.

The news, first reported by the New York Post, prompted Christie to hastily schedule a news conference Tuesday, where he answered more than a dozen questions about the procedure at New York University Langone Medical Center. The surgery was in the morning on a Saturday, and he was back home that day. He held two public events the following Tuesday.

He brushed aside speculation that his effort to slim down signaled interest in the 2016 presidential campaign. His motivation, he said, was to be around long enough to spend as much time as possible with his wife, four children, and any future grandchildren.

"Unlike some of you, they will still pay attention to me whether I run for president or not," he said.

He added: "It's not a career issue with me. It is a long-term health issue with me, and that's the basis on which I made the decision."

After getting advice from New York Jets coach Rex Ryan, who had similar surgery, he decided in September, when he turned 50, to have it himself, he said. But the procedure was delayed because of Hurricane Sandy, he said.

The procedure involves placing a silicone tube around the top of the stomach, limiting appetite.

Although Democrats stayed mum, questions surfaced online about whether Christie appropriately handed over power to Lt. Gov. Kim Guadagno while he was under anesthesia.

"I was in surgery for a total of 40 minutes, I was asleep for 40 minutes, and, no, the lieutenant governor was not in charge for those 40 minutes, I was in charge, and it's a ridiculous question," Christie said.

Christie's weight has long shadowed his career. After a brief hospitalization following an asthma attack on a hot day in July 2011, Christie told dozens of reporters that he has struggled with weight since he stopped playing sports in high school.

He works out four times a week with a personal trainer who comes to his home, he said Tuesday.

In a March poll from Quinnipiac University, 64 percent of New Jerseyans said they were comfortable with an overweight governor.

But weight could make a difference on the more intensely scrutinized national stage. A new book about Fox News chief executive officer Roger Ailes by journalist Jonathan Alter recounts three reasons that Christie gave Ailes for not running for president.

One of those reasons? "I still like to go to Burger King, and I'm not going to lose" the weight, Christie said, according to Alter.

Political scientist Larry Sabato of the University of Virginia pointed out that "it took people about 10 seconds to say he had the surgery because he knew he had to get in better shape to run for president."

The crowd at the news conference that had gathered to watch a school groundbreaking groaned and booed when the first reporter Christie called on asked about the surgery and why he had kept it secret.

The governor apologized to the students at Newark Tech that they had to share this special day with "my waistline." He didn't know that it would be the day his weight-loss plan was "outed."

"In terms of keeping it secret, it's nobody else's business," he said as the crowd of about 100 broke into applause. He said he wouldn't have talked about if the Post hadn't asked him. Only his family, chief of staff, and the top lawyer in the governor's office knew about the procedure.

Online Tuesday, the news was met with notable support.

Jersey Shore cast member Nicole "Snooki" Polizzi, whom Christie has criticized in the past, tweeted: "happy to hear u want to lose weight! If u ever hit the gym & need a work out buddy, call me. good luck!!"

But fat jokes were also omnipresent. Christie has said fat jokes are OK as long as they're funny, and has often laughed along.

On CBS, David Letterman has put Christie fat jokes in his Top 10 lists, and recently Christie went on the show and ate a doughnut.

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

When a former White House doctor criticized the governor after that appearance, saying he could have a heart attack and die, Christie told her to "shut up."

While Christie declined to say how much weight he has lost since the surgery, the Post, in its scoop headlined "The Weight Is Over," cited sources who said he had lost about 40 pounds.

After exhausting the press corps on Tuesday, Christie warned that this was the last time he would address this issue. Don't expect updates, he said.

"I'm not going to tell you how I'm doing," he said.

"This is an intensely personal issue. I'm not going to be one of these guys who's going to write a book."

And he has no interest in being a role model for society in this matter, he said.

"All I want to do is be a role model for my children," he said.

Contact Matt Katz at 609-217-8355 or mkatz@phillynews.com, or follow on Twitter @mattkatz00. Read his blog, "Christie Chronicles," at www.philly.com/christiechronicles.