Two words on lots of people’s lips in the New Year: weight loss. While many average folks worry about what number’s popping up on the scale, for celebs, it’s an obsession. Here are a few who are taking it to the extreme in 2012:

Jennifer Hudson: The American Idol singer, 30, just came out with a book, I Got This: How I Changed My Ways and Lost What Weighed Me Down (Dutton, $25.95). It briefly touches on the Oscar winner’s’s journey from Chicago’s South Side, where she grew up “curvy,’’ to the glare of the spotlight, but seems more like a giant ad for the weight loss company, for which she became an “ambassador’’ in 2010. Despite a penchant for Mexican food, Hudson lost a total of 80 pounds and looks amazing. In a new, very cool digitally enhanced ad for WW, she sings to her old, bigger self. For fans seeking information about her family tragedy -- losing her mother, brother and nephew in a 2008 shooting -- they won’t find it. What you will learn is about how to stay within your “Points,’’ and eat healthy foods like turkey burgers from the Cheesecake Factory and grilled chicken from Texas de Brazil.

Charles Barkley: Not just women worry about the “lbs,’’ as evidenced by a new commercial starring the basketball legend, also a pitchperson for Weight Watchers. “Lose weight like a man,” he says. At his highest, the 48-year-old retired athlete was 350 plus. Weight Watchers Online for Men is an extension of the 45-year-old plan, which includes a points system and support meetings. As for Barkley, he told People last month that he had shed 27 pounds in 10 weeks. No more pizza or cookies for him, and filling food like oatmeal for breakfast is a must.

Mariah Carey: Twins may be the double the pleasure, but being pregnant with them wasn’t always so fun for the singer, who experienced gestational diabetes and edema, swelling of the legs. Since Monroe and Moroccan’s birth in April, Carey has managed to drop 30 pounds with the help of Jenny Craig. A new TV spot shows the much slimmer diva singing her latest song, Make It Happen. “I wrote that song from personal experience,’’ she says. Other Jenny success stories: Carrie Fisher and Valerie Bertinelli. And we hear Jessica Simpson just signed on; she’ll start checking calories as soon as her bambino is born in the spring.

Janet Jackson: Right before the holidays the singer debuted her ads for Nutrisystem’s new custom plan, called Success, chatting about her frustrations with her body and lifelong battle with the bulge: “I have a message for anyone that’s ever struggled with weight loss,’’ she says. “Get on it.’’

Madeleine Marr