Kim Kardashian, who showed off her curves in a body-hugging white YSL dress and Tom Ford heels Thursday in Mexico City at Cosmopolitan mag's 40th Anniversary celebration, wrote on her blog, "Yes, I have gained some weight ... but I guess being happy and comfortable does that to you."

(Life & Style claims she has gained "15 to 20" pounds since she began dating Kanye West in April.) So she's getting back on the diet program she endorses to help shed pounds.

Blogged Kim on Thursday, "I am back in the gym, watching what I eat and that combined with starting QuickTrim again means I'm feeling positive. I just want to be at my target weight and feel good about myself. I hate feeling heavy and lazy and it's not a nice feeling when my clothes don't fit. Just gotta stay focused! Xo"

Her slimming plans seem to be working already. On Wednesday, she tweeted: "Since I started QuickTrim again a few weeks ago, I'm down 6 lbs!!! Yay best feeling. I was getting discouraged but now I'm so motivated!"

USA Today