"I've always known that I'm not Kim and I'm not Kourtney - I've always been O.K. with that," she told the UK edition of Cosmopolitan, while admitting, "I probably thought I was prettier before I entered the spotlight because being compared to somebody else every day does sort of beat up your spirit and soul."
But the comparisons - and critiques - have made her a more confident woman.
"It's made me stronger. I've gained another level of confidence," the 28-year-old " Keeping Up with the Kardashians" star told the June issue.
Kardashian talks about the public hits she took after her dad died and she piled on the pounds.
"I was quickly criticized for not being a cookie-cutter sister like Kourtney and Kim. I lost about 30lbs [in 2009] before I did 'Kourtney And Khloé Take Miami.' I was feeling so good about myself and I was still so critiqued. I thought, 'Oh, my gosh, if I'm not good enough now…' And that's when something clicked in my brain: I have to do whatever is good for me… I feel that I'm healthier [now], but I don't think I'm prettier thinner."
Kardashian has recently slimmed down again but says she'll never be stick-thin.
"I don't expect to be a size 2 nor do I want to be. I'm 5-foot-10-inches, and I like being curvy, but I also like being toned."
Kardashian also opened up about her struggles to have a baby with her husband, NBA star Lamar Odom.
"I just wanted to be, 'Hey, let's have a baby,' and we would just have one. Kourtney did. And I wish that was the way for me. But it won't be. I'll have to take hormones. I do want to have a baby, but I don't feel the urgency to have one this very moment," she said.
When she does have kids, Kardashian said she won't be a "momanger" like her own mother, Kris Jenner.
"[Once my mom told me] I was gaining weight, but she was talking to me as a manager, like I was ruining a brand deal," Kardashian told Cosmo. "It's hard to understand that and it's more hurtful when it's coming from my mom."
Now that she's older, Kardashian said she feels sorry for rather than resents her mom, especially when she and her sisters "gang up" on her.
She also admitted that Kim is her mom's favorite.
"It doesn't bother me. They're so similar - they could be the same person," she said.
As for her pregnant sister Kim, Kardashian loves the rapport the family has with the baby's father, Kanye West.
"I think Kanye knows how to deal with Kim really well. Because we've known him for so long, he'll come to us if he wants advice on a birthday present or something. I like that. Kris [Humphries, Kim's ex-husband] wouldn't even talk to us. I love that with Kanye we have that friendship. Because when you're with one of us, you're with all of us."