Britney Spears is in fighting form on the latest cover of Shape magazine.

Wearing a white cut-out bikini, the 31-year-old Spears shows off her flat, toned abs, and looks as great as she did during her “Baby One More Time” days back in 1999.

The mother of two has lost a significant amount of weight in recent years, and her weight has been up and down throughout her career.

Fourteen years after the start of her career, Spears admits that keeping her body slim and trim is not as easy as when she was a teenager.

"Dieting is tough," she admits, "because my specialties are spaghetti, brownies and chocolate chip cookies. I try not to make those too often or I’ll eat the whole bowl of dough.”

Spears follows the Nutrisystem weight loss program, where meals consist of a shake for breakfast and lunch plus a dinner of protein and vegetables, in order to stay healthy.

The singer is also maintaining an intense exercise regimen. She is set to perform in Las Vegas in the near future. Though the date has not yet been confirmed, Spears is hard at work preparing for the shows.

“I’m doing 90 minutes of yoga twice a week in addition to a lot of cardio — hourlong sessions three times a week with my trainer, Tony Martinez,” Spears said. “The [Vegas] performances won’t be simple — they’ll be a massive party from start to finish, and to pull this off, I have to be in top condition and running at full speed."

The “Scream and Shout” singer also revealed a love-hate relationship with her derriere. "I like it, then again, I hate it," Spears says. "I’m in my 30s now, so I have to work harder to keep it ‘up.'"

Check out Britney Spears on the latest cover of Shape.