Sailor Brinkley Cook, Alexa Ray Joel Talk Body Struggles, Posing With Mom Christie Brinkley in 'Sports Illustr

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Christie Brinkley's daughters, Sailor Brinkley Cook and Alexa Ray Joel, are getting candid about dealing with body issues growing up.

Sailor, 18, and Alexa, 31, recently posed with their supermodel mama for Sports Illustrated's famous swimsuit issue, and both reflected on how far they've come when it comes to their self-esteem. Sailor Instagrammed a priceless photo of the two sisters with 63-year-old Christie -- all rocking sexy swimwear -- on Monday.

"I've had issues with my body image since before I can even remember," Sailor shares. "I grew up not loving how I looked and felt held back because of it."

WATCH: Christie Brinkley Returns to the 'Sports Illustrated' Swimsuit Issue With Her Daughters -- See the Pics!

"For some reason I still looked in the mirror and always somehow found something to pick on," she continues. "I went from being 'too fat' to 'too thin' to 'too muscular' and I never felt satisfied. My body and I have been through it all."

Though recently, the beautiful blonde says she's been "liberated."

"I am healthy, I treat myself well, and for that I'm happy," she writes. "I've looked in the mirror and been able to LOVE the things about my body that beauty norms deem 'undesirable.' I now have grown to know that my body is worthy of so many great things. I don't need to be a size 0 to believe in myself. My body carries me each and every day, it loves the people I love, it holds what makes me healthy and strong, it bends it shakes it runs and it CHANGES. That is OK and that is beautiful."

Meanwhile, Alexa shared her own confident bikini pics, and talked about learning to accept herself.

"This was a lesson in learning to let go, take the plunge, and embrace myself from both the inside AND out -- which is something I struggle with each and every day," she captioned one Sports Illustrated snap. "My purpose is to now pass along this lesson of unconditional self-love and self-respect to every woman who's willing to listen."

She also posted a sexy selfie with a positive message for all women.

"Let's STOP degrading and START celebrating ourselves and others, from both the inside AND out," she writes. "There's far too much degradation, competition, insecurity, and unhealthy standards associated with women and their bodies -- particularly on social-media. ... I don't have a completely flat tummy, or cellulite-free thighs... nor am I a model's height or shape. Neither are hundreds of millions of other beautiful women out there. SO WHAT? Does it really matter, in the end? All that matters is how YOU feel about yourself."

"Set your own standards of beauty; both internally and externally," she adds. "All of those unrealistic-looking, photoshopped images are nothing more than white noise, playing off of your own insecurities in order to make a buck. Don't let them affect you. DO YOU! We are all perfect, just as we are."

WATCH: Christie Brinkley and Daughter Sailor Are Totally Twinning in Matching Overalls

Last August, Sailor spoke out against online bullying, specifically, those comparing her to her legendary mom.

"Believe it or not, I am my own person with my own beliefs and own thoughts and my own face!" she hit back on Instagram. "Eyes smile teeth forehead! All mine! The whole shabang! Yes, I am so fortunate that my mother is my mother.. And she will always be an inspiration to me... But being constantly compared to her 50+ years of success at only 18 years old? And being told I could never amount to what she was and what she looks like? Doesn't feel great."

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