By Gillian Telling Ana Calderone
September 22, 2014 12:00 PM

Meghan Trainor didn’t have an anthem like “All About That Bass” when she was growing up, so she had to write it herself. “I got a message from a fan that said, ‘I was anorexic and cut myself … until I heard your song,’ ” says the 20-year-old songwriter. Raised in Nantucket, Mass., Trainor was friends with the “pretty, popular girls,” but “I would destroy myself and say ‘I’m so fat,’ ” she says. Her mother, Kelli, would remind her “to not worry about size and love myself.” Though she had written hits for Rascal Flatts, Trainor was no pop star—until L.A. Reid signed her to record “Bass.” With the single getting more than 50 million hits on YouTube and topping iTunes (her debut EP, Title, is out now), she sometimes thinks about the boy in junior high who suggested she lose 10 lbs. “He probably hates himself now,” she says, laughing. “I’m beautiful and happy. And I’m not going to change.”