It's no secret Kim Kardashian is obsessed with her figure — take a look at her Instagram full of selfies if you need proof. But according to a childhood friend of the reality star, that obsession is nothing new.

"At 13, we started to become more aware of ourselves. We began wearing make-up and started dieting," Kim's former BFF Nikki Lund told 'Heat' magazine. "It was mostly the Atkins and the South Beach Diet. We did the Cabbage Soup Diet and we'd be there boiling great big vats of cabbage. We were like, 'Yes, we're going to be thin.'"

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Kim and Nikki as teenagers.

The pre-teen portion control eventually took its toll on Nikki, who developed an eating disorder. But it wasn't just weight loss that had Kim consumed.

"[She] was always saying her nose wasn't perfect. I thought she was nuts," Nikki told 'Heat.' "Every girl has something they don't like."

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Kim in March 2015 and Nikki in November 2014. (Photo Credit: Getty Images (2))

While Kim has denied getting plastic surgery on her face, she admits to using Botox. She's also been candid about her body-image struggles while pregnant with daughter North.

"For me, having people criticize what I wore and looked like when I was pregnant — that was hard," she previously shared with 'British Vogue.'

RELATED STORY: Kim Kardashian Snaps Another Waist Training Photo — Shows Off Incredible Hourglass Figure!

She's also confessed to being envious of sister Kendall Jenner's skinny frame. "I'd love to swap bodies with Kendall for just a week, just to look from that little bit higher up and fit into everything perfectly," she told 'LOVE' magazine.