The friends, who both recently split with their respective musician boyfriends Justin Timberlake and Strokes drummer Fabrizio Moretti, are said to have made an agreement to get into shape to help them find love.
A source told Britain's Grazia magazine: 'Cameron's new regime started as a joke between her and Drew but now she's keeping it up.' Both actresses have noticeably lost weight since becoming single and it has sparked rumours they could be feeling under pressure to attract new men.
Hollywood relationship therapist Betsy Spier said: 'Hollywood women lose weight after a split because of the stress. They 'up' their training to deal with emotions.
'Exercise releases feel-good hormones; it shows men 'I don't need you' and it improves their body for the next catch.'