Model Katie Willcox: I Booked More Jobs at Size 14 than Size 6

"I was losing all my clients because everyone was saying, 'Oh, you're too small now, we want you fuller,' " Katie Willcox tells PEOPLE

Photo: Bradford Willcox

Katie Willcox started out as a plus-size model at the age of 17, and would soon realize that the industry was making her unhealthily obsessed with her weight.

“I was always a bigger-framed person,” she tells PEOPLE. “When I got scouted for modeling, they were like, ‘Oh you’d be perfect for plus-size modeling.’ That totally shattered my self-esteem. In high school, that’s the last thing anyone wants to hear. It’s like, I’m trying to like myself and you basically just called me fat.”

When Willcox, now 30, began working as a model, she was shocked at the eating habits of the straight-size models she encountered on sets.

“When I saw models in real life, I was like, oh my God,” she recalls. “I had no idea they had to be that small and that thin. When I would go on shoots, I would notice a lot of them don’t eat lunch, or they have just lettuce, or very small amounts of food. And I was like, oh cookies? Awesome.”

Willcox actually began booking more jobs when she gained 25 lbs. as a freshman in college, bringing her weight up to 200 lbs.

“When I went to my agency they were like, ‘Oh you look great!,’ because I was now a size 14, which is the sample size that works the most for plus-size modeling,” she explains. “I started working well, but I still didn’t like the way I felt. I felt really unhealthy and depressed. But I was getting rewarded for it.”

It wasn’t until Willcox met her husband Bradford on the set of a photo shoot for Torrid that she decided to focus on getting healthy.

“He helped me realize it doesn’t matter what size I am for someone to think that I’m beautiful,” she says. “Over time he helped me figure out how to be healthy, and that started to make me feel better on the inside.”

Willcox dropped down to a size 10/12 – a healthy size for her natural 5″9′ frame – but this meant she was no longer considered big enough for plus-size modeling.

“I was losing all my clients because everyone was saying, ‘Oh, you’re too small now, we want you fuller,’ ” she says. “I was shocked because I thought I looked great. I was like, why am I not valued when I look my best and I feel my best?”

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Determined to stay in the modeling industry, but not wanting to gain weight back, Willcox decided to drop to a size 6 to qualify for the “women’s” category of modeling, which mainly constitutes catalog work.

“I did a meal delivery service, and it was terrible!” she says. “It was the tiniest portions, and I was timing myself to see when I could have my next meal. At the time I was working out three hours a day. I got to a point where I could fit into size 6 pants, but the buttons wouldn’t close across my hips.”

After nearly starving herself, Willcox hit a low point when she found herself desperately licking leftover frosting from a baking sheet.

“I was like, what is going on?,” she says. “I had this wakeup call that this is not who am I at all. I had a moment where I wanted to quit. Why am I giving so much to this industry that doesn’t give me anything back?”

The Los Angeles-based body-positive advocate decided that instead of quitting the industry, she wanted to change it, and came up with the idea for Healthy is the New Skinny, which is now a thriving social media movement and lifestyle brand.

“I started to talk about my experiences on a blog, and the models were hitting me up left and right and saying, ‘I saw this and I wanted you to know I struggle with this every day,’ and were sharing their stories with me,” says Willcox. “Every model feels this way, but you can’t talk about it because you risk pissing off your bookers and then they won’t book you.”

Willcox left Ford Models and founded her own modeling agency, Natural Model Management, in 2011 to welcome women with “real” bodies. It now represents over 30 models, including herself.

In addition to changing the modeling industry, Willcox is determined to teach young girls to love their bodies, and regularly gives speeches about healthy eating and body confidence at schools across the country.

“No matter what size any of us are, as women, we’ve always felt this pressure to be skinny,” she says. “There’s this perception that you’re only healthy if you look like what the media’s portrayed health to look like. It’s inspiring to see that girls are starting to wake up to the fact that these feelings aren’t natural to us, it’s been taught. That’s been my main goal, and to say, we can challenge that.”