Credit: Jean Baptiste Lacroix/

Kourtney Kardashian has a new fitness battle on her hands.

The reality star has packed on the pounds since she stopped breastfeeding son Mason, 16 months.

"Wow. I have gained almost 10 pounds since I stopped breastfeeding," Kardashian, 32, wrote Monday. "Time to step up my workout game & get over to Rite Aid for some Quicktrim!"

Even though the 32-year-old mom credits her son's breastfeeding for helping her lose her baby weight, sister Kim hasn't always been a fan of the practice.

Last June, Kim, 30, came under fire for writing on her Twitter page: "EWW I'm at lunch, the woman at the table next to me is breastfeeding her baby with no cover-up!"

She later defended her tweets: "My sister breastfeeds! It's a natural, beautiful thing. But she covers herself [and doesn't do it] with her boobs exposed."