Mental health experts hypothesize that the pandemic prompted some youth to feel isolated, lonely and out-of-control. Some coped by seeking to have control over their own behavior, said Emily Pluhar, a pediatric psychologist at Boston Children’s Hospital and instructor at Harvard Medical School.

“You take a very vulnerable group and put on a global pandemic,” she said. “The eating disorders are out of control.”

In the C.D.C. study, the agency said that the proportion of eating disorder visits doubled among teenage girls, set off by pandemic-related risk factors, like the “lack of structure in daily routine, emotional distress and changes in food availability.”