"I think we all have our good days and our bad days in how we feel about ourselves," began Aguilera, 40. "Entering this business, I hated being super skinny. Once I turned 21, I started filling out a little bit, and I was loving my new curves."
"I appreciated having a booty. I've always said that women are way more interesting to look at than men!" she continued. "I have a hard time looking at the early pictures of myself because I remember feeling so insecure."
The Grammy winner admitted that she "would never want to relive" her 20s.
"You're so in your own head and finding your confidence," she explained. "As you age, you stop comparing yourself to other people and start appreciating your own body and owning it."
Aguilera said beauty is ultimately about "accepting yourself."
She added, "As much as I also love being a glam girl and playing dress-up for the camera when it all comes off, that's what's ultimately most rewarding -- being able to feel really good about who's staring back at you in the mirror, because you're owning all of it."
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The "Fighter" singer revealed she's been doing some "self-reflecting" during the past year and took a look back at her career, which began when she was only 7.
"I have this massive trunk of old diaries that I've literally kept from the past 20 years of my life. I was able to catch up on them and do some self-reflecting," Aguilera said. "It really forced me to be silent and take a look at myself."
"In some regard, I wasn't happy with a lot of things, and it's scary to face those feelings that, under normal circumstances, you don't have time to face because everyone is going, going, going," she continued. "That grind is praised, but I think we're all understanding that having moments to self-reflect and just breathe are crucial."
Aguilera explained how her experience as a child star, in particular, has stuck with her.
"I've been working since I was 7 years old," she told the magazine. "When I'm not working, there's a heavy amount of guilt that I feel. It's been embedded in me since I was little -- you're shamed if you don't want to keep up. As a child [entertainer], you're all pitted against one another, and other children are all about that grind too. It's a weird space to grow up in.
The "Beautiful" singer went on to add that she's "not ashamed" to admit she's had "dark moments," including childhood trauma and mental health struggles.
"I experienced a lot of trauma in my childhood -- I've spoken very openly about it," Aguilera said. "But I think that was just part of my path. I've definitely had struggles in the past with depression and anxiety -- it's a constant battle to overcome a mind that is anxious, a mind that is always second-guessing."
Aguilera said her "fighting spirit" and "honestly" have helped her be successful in the industry.
"I'm proud of my honesty," she shared. "It's a really hard thing to stick to in this business, especially when you've grown up under a microscope at a time when society was very critical of young women. I've had to work through a lot of insecurities in front of everybody. Every setback has catapulted me forward. I think that's my fighting spirit. And, at the end of the day, living that truth and being honest has always propelled me forward.
"No matter what I've been through -- successes, childhood trauma, hardships -- I still have a fighting spirit," she added. "I never want to stop learning and growing to be the best person I can be."