The actress wanted to shift some weight before she flew out to Hawaii to shoot new movie 'Just Go With It' so enlisted the help of celebrity trainer Tracy Anderson, who recommended The Baby Food Cleanse eating plan, which involves 14 portions of pureed food a day followed by a healthy adult dinner.

It is said to have worked for Jennifer - who has previously admitted to enjoying dairy, coffee and wine - as she has lost 7lbs.

A source told Britain's Grazia magazine: "While in Europe last month, Jen had relaxed her usually strict diet regime. She knew she had been indulging, and seeing as her upcoming role required her to wear lots of little dresses, she wanted to be at her physical peak."

Tracy - whose celebrity clients include Gwyneth Paltrow and Courteney Cox Arquette - is very impressed with Jennifer's progress.

She said: "She's doing really well. Nobody says they only want one specific thing changed. They want the whole toning package."

The diet includes fruit smoothies, pureed oatmeal and pears with cinnamon, soups containing dandelion greens and a dinner of lean meats and vegetables and Tracy swears by the eating plan.

A source said: "Tracy is all about 'clean eating', which means no oils, spices or salt. With 'baby eating', the food is easily processed by the body. Tracy believes efficient digestion equals quick weight loss. But this is a temporary diet for shifting a few pounds quickly, before going back to a normal, healthy eating plan."