Lady Gaga says she battled bulimia as a young woman.
The pop star says she was so obsessed with being a "skinny little ballerina," she used to make herself vomit after meals in high school.
Gaga confessed to her eating disorder during her surprise appearance at a young women's conference hosted by a Los Angeles school.
The "You And I" singer spoke candidly at the open forum, led by Arnold Schwarzenegger's estranged wife Maria Shriver.
Addressing Gaga, one teen student said: "I struggle with body issues, and I know you're so confident in the way you dress.
"And I am wondering how you deal with such issues."
After a short silence, the eccentric New York singer replied: "I used to throw up all the time in high school. So I'm not that confident.
"And maybe it's easier for me to talk about it now because I don't do it anymore.
"I wanted to be a skinny little ballerina but I was a voluptuous little Italian girl whose dad had meatballs on the table every night.
"I used to come home and say, 'Dad, why do you always give us this food? I need to be thin.' And he'd say, 'Eat your spaghetti.'"
Maria then asked Gaga how she eventually conquered her eating disorder.
The star answered: "It made my voice bad, so I had to stop. The acid on your vocal chords, it's very bad.
"But for those of you who don't sing, you maybe don't have that excuse until it's too late. It's very dangerous."
She also reassured students that not all female celebrities are as stick-thin as they appear in magazines.
Gaga said: "Every video I'm in, every magazine cover, they stretch you; they make you perfect. It's not real life."