The 32-year-old singer has been eating a lot of junk food recently and not exercising enough, reported Showbizspy.
"Britney has gained close to 30 pounds, and she has got a lot of cellulite on her legs and stomach. To disguise her belly onstage, she wears a one-piece leotard made out of a shaping material for a slimming effect," a source said.
"Britney isn't using her home gym, and she is gorging on junk food," it added.
But Spears apparently has a plan to drop her extra weight.