It was barely a month into the pandemic when Dr. Tracy Richmond, the director of the Eating Disorder Program at Boston Children's Hospital, knew something bad was happening in young people.
Richmond said her team was getting an unusual number of requests for help with eating disorders in mid-April 2020. "By summertime," she said, "we were bursting at the seams."
The problem is not limited to the Boston area. The National Eating Disorder Association reports a more than 53% increase in call volume to its helpline since the start of the pandemic. Just over a third of those patients are ages 13 to 17, and about 36% are 18 to 24 years old.
The National Association of Anorexia Nervosa and Associated Disorders, too, has seen a 50% jump in calls from teens and their parents since the pandemic began.
Experts attribute the rise in unhealthy and potentially dangerous eating habits in teenagers to a combination of social confinement during lockdown and a feeling of losing control.
"Isolation impacts adolescents more because so much of their lived experience is socializing with other people," said Lynn Slawsky, the executive director of National Association of Anorexia Nervosa and Associated Disorders.
When lockdown occurred, kids "didn't have their sports teams if they were an athlete, or they didn't have the theater programs if they were an actor," Richmond said. "All of a sudden, they felt really out of control. And for many of our patients when they look for something to control, they look towards eating and food."
"Many of the patients we're seeing would never have developed an eating disorder if it weren't for the pandemic," she added.
Dr. Natasha Burgert, a pediatrician in the Kansas City, Missouri area, noticed the problem particularly affected her high-achieving young patients who'd been otherwise accustomed to thriving in school or in sports.
"This pandemic has just thrown them for a loop," she said. "They don't have the routine of school to give them a lot of comfort."
In many cases, Burgert theorized, "controlling eating behaviors becomes a proxy for the loss of control in other parts of their life." Often, this results in severely limiting food intake.
Isolation was a trigger for Chloe Melton's problematic eating last year.
Chloe, 16, of Atlanta, said it was easier to have healthy eating habits when school was in session, in person.
"Usually when you're at school, you have classes going on, you have a specific lunchtime," Melton said. Once the pandemic hit, her environment changed, creating a "perfect storm" for an eating disorder to thrive.
"I could control every single meal," Melton said. She turned to restrictive eating behaviors, particularly fasting.
During an interview with NBC News, Chloe declined to share how much weight she lost, but by the summer, her heart rate fell dangerously low — fewer than 40 beats per minute — and she was hospitalized.
An extremely low heart rate, known as bradycardia, is common problem in people who lose too much weight or lose weight too quickly, Richmond said.
"It's an extreme marker of malnutrition," she said. "Your body is saying, 'I have so little nutrition on board that I'm going to slow the heart down to the minimal rate that will sustain life.'"
Chloe spent six weeks in a treatment facility, where she was diagnosed with anorexia, and remains in the recovery process.
"You have to wake up and say, 'I'm going to make this choice'" to be healthy every single day, she said. "That's why it's so hard. And that's why so many people relapse." She still works with a dietitian and therapists on a weekly basis.
Burgert said many of her young patients with disordered eating tend to be white, upper middle-class girls, simply because that group makes up the bulk of her patient population.
But Richmond cautioned against any stereotypes. "We're seeing kids from all sorts of racial and ethnic backgrounds, all sorts of socio-economic backgrounds," as well as a spectrum of ages and genders.
"Think about someone whose family has lost a loved one or has really been financially impacted," Richmond said. "That's a perfect setting for an eating disorder to develop."
This story first appeared on NBCNews.com.