The stakes are high for Christie, with medical professionals and campaign strategists alike suggesting there is no more serious barrier to his personal well-being and national ambitions than his weight.
It's not about politics, he said. It's about turning 50 and wanting to be around as his children grow up.
"This is a hell of a lot more important to me than running for president," Christie, a father of four, said at a news conference in Newark. "This is about my family's future."
Christie, who appeared thinner than he did earlier this year, said he decided around the time of his birthday in September to have the surgery and initially planned to have it done in November. But Superstorm Sandy's destruction in New Jersey pushed back the procedure until February. In the operation, a band was surgically placed around his stomach to restrict how much food he could eat.
Christie has not previously disclosed his weight, and he didn't on Tuesday. But it has been an issue throughout his political career. Comedians have often made fun of it, and in interviews with David Letterman, Oprah Winfrey, Barbara Walters and others, Christie has both joked about the issue and said solemnly that he was trying to shed pounds.
During a February appearance on "The Late Show with David Letterman," the governor pulled out a doughnut and said his girth was "fair game" for comedians.
Over the next few days, he was asked repeatedly about his weight. At one point, he said he had a plan. "Whether it's successful or not," he said, "you'll all be able to notice."
The next day, he responded angrily to comments from a former White House physician who said she hoped he would run for president but worried about him dying in office. The governor said the doctor should "shut up."
Ten days after that, on Feb. 16, Christie had the surgery. He said the operation lasted 40 minutes and he was home the same afternoon. He was back at work on Feb. 19 for a full day of events.
Christie, who is in the midst of a re-election campaign, said he has been eating less because he hasn't been as hungry. He also has been working out with a personal trainer.
He said he had told only a few top staffers - not his communications office or campaign staff - and his communications director was caught by surprise Monday when a New York Post reporter asked directly if he'd had the procedure. The Post first reported the surgery on Tuesday. Christie said he'd used an alias at the hospital.
Christie said he never intended to make a public announcement and that he was "not going to be the guy who writes a book" about losing weight. The Republican, who has been a fixture in the national media spotlight, said the scrum of reporters at his news conference was "silly" and "ridiculous" at a time when there are other things going on.
He said he tried other ways to lose weight for years, but none seemed to work.
"It's not a career issue for me; it's a long-term health issue for me," he said.
Still, it's a way to confront a significant hurdle in his indisputable quest to emerge as a key leader in the Republican Party. He's in the top tier of those considered potential contenders for the presidential nomination in 2016.
Weeks after the surgery, Christie launched an aggressive national fundraising tour, fueling speculation that he's laying the groundwork for a White House bid.
In a country facing an obesity epidemic, more than 220,000 stomach-reducing procedures of various types are performed each year. Gastric bypass, sometimes called stomach stapling, is the most common, where surgeons shrink the stomach's size and reroute food to the small intestine. Christie had gastric band surgery. It's best known by the brand name Lap-Band, and is a less invasive alternative in which an adjustable ring is placed over the top of the stomach and tightened to restrict how much food can enter.
The adjustable Lap-Band has been available in the U.S. since 2001 for the most obese patients, and in 2011 the Food and Drug Administration expanded approval to somewhat less obese patients.
Candidates for gastric banding must have a body mass index of between 30 and 40 - plus a weight-related medical condition, such as diabetes or high blood pressure - or a BMI of 40 and higher. They also must have previously attempted to lose weight through diet and exercise.
"If you eat appropriately and chew your food, it works nicely," said Dr. Christina Li, a bariatric doctor at Sinai Hospital of Baltimore. She said Christie has the resources to have people help him eat right and get exercise. While the band is removable, she said patients are told to adjust to having it for the rest of their lives.
Li said risks include infection, and that it does not work for all patients.
Dr. Jaime Ponce, who practices in Dalton, Ga., and is president of the American Society for Metabolic & Bariatric Surgery, said people who have the procedure Christie had often lose 1 to 2 pounds per week.
Christie's procedure was performed by Dr. George Fielding, head of NYU Medical Center's Weight Management Program, who did the same procedure for New York Jets coach Rex Ryan three years ago.
"It basically teaches you how to eat like a human," Ryan said of the device in an interview last week with The Associated Press. "The Lap-Band goes: 'No, no. You're only going to eat this or that,' and it trains your body how to eat right," said Ryan, who said he has lost 115 pounds from his pre-surgery weight of 348.
Few significantly overweight presidential candidates have succeeded in the modern political era, when television became a major factor in shaping voter attitudes. There are disputed reports that President William Howard Taft couldn't fit in a White House bathtub a century ago, but only a handful of presidents since have been considered obese. President Bill Clinton struggled at times with his weight, but he was substantially slimmer than the New Jersey governor.
"This has nothing to do with politics," said Christie adviser Bill Palatucci. "He said that he's doing this for his family and that's the right reason."
Backers publicly argue that Christie answered any questions about his weight's political impact in 2009, when he beat Gov. Jon Corzine despite the Democrat's reference in an ad to Christie "throwing his weight around" to get out of traffic tickets. Supporters say Christie's openness about his struggle is part of an authenticity people admire in him.
The governor's allies, medical professionals and even history suggest that his weight presents both practical and political problems.
"Gov. Christie's weight is an issue the same way that any candidate or official's health is an issue," said Michael Dennehy, a New Hampshire-based Republican strategist and veteran of presidential politics. "Anyone running for president will need to comfort Americans with an overall healthy picture for their future."
Mulvihill reported from Haddonfield, N.J., and Peoples from Providence, R.I. AP Medical Writer Lauran Neergaard in Washington, AP writers Thomas Beaumont in Des Moines, Iowa, and AP Sports Writer Dennis Waszak in New York contributed to this report.