Kim Kardashian and her sisters waged a campaign of LIES when they claimed they got their rock hard bikini bodies from a diet pill called QuickTrim ... this according to a new $5 MILLION lawsuit.

The point of the suit -- a bunch of people in NY claim there's no POSSIBLE way QuickTrim could've helped Kim, Khloe and Kourtney lose weight ... because the main ingredient is caffeine. According to the suit, "The FDA has determined [caffeine] is not a safe or effective treatment for weight control."