Updated

Kim Kardashian and her sister Khloe face a possible class-action lawsuit over their diet product QuickTrim, which detractors say contains high levels of caffeine, an ingredient that’s “not safe or effective for weight loss.”

Kim and Khloe caused a stir over their paid endorsement of the product, which features a picture of bikini-clad Kim.

It has reportedly generated $45 million in revenue since they struck the deal with New Jersey-based Windmill Health Products in 2009.

Law firm Bursor & Fisher is preparing a suit against Windmill and the marketing claims made by the Kardashians. An e-mail it sent to product users included a link to the firm’s Web site, which states, “The active ingredient in QuickTrim weight loss products is a large dose of caffeine . . . The FDA has determined that caffeine is not safe or effective for weight loss.”

In January 2010, Kim said she used QuickTrim to shed 15 pounds in weeks.

Last year she tweeted that she was using it to get in shape for her wedding, and Khloe also claimed she lost 15 pounds.

Go to NYPost.com for the full report.