Kim and Khloe Kardashian are big -- er, skinny -- fans of QuickTrim!

In exclusive, unreleased commercial footage obtained by, the reality show sisters stroke their bodies seductively for the camera!

See photos of Kim's best booty moments through the years!

The QuickTrim commercial -- which was shot in late November in Miami -- features Kim, 29, wearing nothing but a white button-up shirt and Khloe lying in bed with nothing but a white sheet covering her. The two also lounged poolside in bikinis.

Kim says the diet product -- which the two had been working on since July -- has helped her reach her fitness goal.

"Now I am toned, fit and at a healthy weight, and I just need to keep it up," Kim wrote on her website, alongside photos of her and Khloe wearing the bikinis from the shoot.

Khloe, however, isn't satisfied with her body just yet.

"I've gained a little love weight," Khloe -- who had lost 20 pounds before marrying Lamar Odom in September -- admits. "But I know by this summer I will have my ultimate bikini body. But I'm still happy!"

The commercial will begin airing in January.