The pop star co-judges on Simon Cowell's hit US TV talent show The X Factor with Simon, Demi Lovato and L.A. Reid.
Britney began her post last week and is committed to remaining in great shape throughout the season.
'Britney has been on an extreme diet and exercise regime,' a source told British newspaper The Sun. 'She has been cutting out carbs and replacing meals with juice drinks. She was doing several hours of exercise a day before the launch and is trying to stick with the regime.'
It is rumoured that Britney was afforded unusual allowances, such as taking breaks whenever she wants, in the multimillion-dollar contract that she signed with Simon.
The songstress walked off set on her first day leaving an empty judging seat for over four contestant performances.
Britney contends that she's enjoying herself on the show.
'Britney walks off??? LOL was just taking a little break people. I am having the BEST time!!!' she posted on Twitter last week.
Tagged in Britney Spears The X-Factor U.S.