But they keep it to themselves. They don't want to share their secret, because they know it could be deadly.
Erin Akers thought she alone held the secret when she was in high school.
"I dropped a significant amount of weight to the point when I came back, everyone at school said something," Erin said. "'You look great, wow, what have you done?' Well, diet and exercise of course. That's the only way to lose weight."
But that wasn't really how Erin did it.
She won't reveal how much she lost. But it turns out many other young women have the same "get skinny" secret.
"I realized it made me lose weight, and I just kept on doing it," said Patience Hollinden. "By the time I was 14, I was hooked."
Their secret has a name. It's an eating disorder called diabulimia.
The women are type 1 diabetics. They control their disease with insulin shots. But they discovered that by withholding their insulin, their bodies couldn't process food.
"It got to the point where injecting insulin felt like taking a shot of fat to me," Patience said. "In my mind I didn't understand that insulin was good for me. It became the enemy."
They felt lousy, but they lost weight.
"Your nerves are dying and your organs are starting to shut down slowly," Erin described. "It's what's known as diabetic ketoacidosis. It's the big bad in the diabetes world."
Erin thought she could manage it, taking herself to the brink, until during one of her many trips to the hospital, her heart stopped beating.
A nurse revived her and she truly woke up.
"Dying. Dying was the big thing for me," she said. "Physical pain, I could deal with. But the idea of hurting the people I loved most finally clicked."
Erin's mother Dawn did her research and already pinpointed the name diabulimia. But finding help was a challenge.
"When I first went to look for treatment for Erin, there were no programs in the United States for diabulimia. A lot of the treatment centers I contacted wouldn't even take her because she had type 1 diabetes," Dawn said.
There were few options for an eating disorder that turned out to be incredibly common. Dr. Mehri Moore of the Moore Center in Bellevue treats diabulimics.
While the patient population is low, Moore said studies find the eating disorder is rampant.
"Preteen diabetic patients we see somewhere around 10 to 15 percent, teenagers up to 25 percent, late teens and young adult somewhere around 40 percent," she said.
Erin finally found treatment and wanted it to be easier for other girls. She started a Facebook support group that now has more than 600 members.
And at 23-years old, she is the CEO of the nationally recognized Diabulimia Helpline.
Staff meetings include Erin, her parents, and Patience. It might look small, but what they've accomplished is huge.
They've helped establish diabulimia treatment programs. They host conferences around the country.
And Erin's biggest accomplishment is the ability to look in the mirror, and know that while there are days she doesn't like what she sees, she still loves who she is.
"It's a reflection of my skin and my body. Not my heart and my soul," she said.