The 20-year-old model discusses this sensitive topic as she gets ready for the Victoria's Secret Fashion Show
Credit: Christian Vierig/Getty Images

Bella Hadid knows that as a top model for brands like DKNY and Calvin Klein, and now especially as she prepares to walk in her very first Victoria’s Secret Fashion Show, her body is often going to be on display — and subject to scrutiny. But she’s shutting down any critics of her weight because, she says, she’s worked hard for her figure.

“I have lost weight and gained weight,” the model tells PEOPLE exclusively during her fitting for the Victoria’s Secret Fashion Show. In a few weeks, the 20-year-old will be walking in the lingerie show in Paris for the first time wearing two ensembles. How she will look is on her mind, as the issue of weight came up during a discussion about feeling confident on the runway while only wearing underwear.

RELATED VIDEO: See Bella Hadid Walk her First Chanel Runway!

“My weight fluctuates so much,” she says. “I really didn’t mean to [lose weight]. Like I want boobs. I want my ass back. But it’s not my fault. My weight fluctuates and so does everybody’s and I think that if people are gonna judge, that’s the worst you can possibly do because everybody is different.”

Slaven Vlasic/Getty Images for Victoria’s Secret
| Credit: Slaven Vlasic/Getty Images for Victoria's Secret

She says she lost weight “accidentally” by adhering to a strict diet and intense exercising regimen. “I worked out so hard and everybody is like, ‘Oh, she looks so skinny blah, blah, blah,” she says. “But I think that if you just stick to something you can really achieve so much. I’ve been eating hard protein every day, and working out for three hours every day. It’s crazy but I think that you know if you set your mind to something I think you can succeed.”

And even when she travels a lot for work, she sticks to her routine. “I like to eat healthy and not eat crazy plane food,” she says. “I like to still make sure my diet is good and I stay hydrated and stuff. That’s basically all I do.”

Bella Hadid wears a cleavage-bearing, body-hugging denim outfit when out and about in New York City
Splash News Online
| Credit: Splash News Online

But she still has cheat days, she admits. “I’m going to eat pasta right now,” she says after wrapping up her fitting at the Victoria’s Secret headquarters. “If you want to have a piece of bread, go have a piece of bread.”

As for training, she works out with Rob Piela at Gotham Gym, the same man who trains many of the VS models, including sister Gigi Hadid. “He’s really the best,” says Hadid. Her only rule is that she must work with him one-on-one. “I literally can’t work out with anybody,” she says. “It has to be me and him. If I am working with other people, I freak out.”

Right now, other than her diet and workouts, she’s focusing on getting down the Victoria’s Secret runway feeling confident. “I think every single person in the world has insecurities,” she says. “It’s crazy because I think that when other people look at all of the VS models or all of the girls [who] are walking, they’re like, ‘They’re not human. They don’t have any insecurities.’ But I think every single girl [who’s] going to be walking probably has an insecurity.”

Bella Hadid bears her sexy midriff when out walking in New York
Splash News Online
| Credit: Splash News Online

As for hers? “I wish my ass was bigger,” she says.

Ultimately, she just wants the whole VS fashion show experience to go well. “I just hope when I am out there I am not too nervous about being in my lingerie,” she says.

Find out soon: The Victoria’s Secret fashion show will air on December 5 on CBS.