Kim Kardashian is making sure her booty stays in tip top shape by heading to Pilates class in Los Angeles. Love those flip flops!

The 31-year-old reality star may be working off some stress after the Kardashian clan reportedly lost two big deals ... a Kardashian-themed magazine with American Media Inc. and a Kardashian Barbie doll line from Mattel.

According to the NY Post, momager Kris Jenner's demands killed the deal. The source tells the paper:

    "AMI chief David Pecker made it clear that there was no way he was going to tell his editors what stories they could and couldn't do."

As for the Barbie doll line, a rep for Mattel says:

    "As popular as the Kardashian sisters are, at this point in time we are not manufacturing Barbie-branded Kardashian dolls."

Let's hope the Pilates class is exactly what Kim needs to get through these tough times.