The teenage pop star ran off during the group's show in Pennsylvania on Monday (08Jul13) and was seen vomiting at the side of the stage. He later regained his composure and rejoined his bandmates to complete the rest of the concert.
Online gossip suggested Styles fell sick after drinking too much alcohol, but the singer insists his problem was not booze-related.
He called into Britain's Radio 1 station from the band's tour bus on Friday (12Jul13) and explained what happened to his friend, host Nick Grimshaw, saying, "I think everyone thinks it's because I was drinking but it was actually because I ate, I had dinner too close (to stage time) and I was just so full."
Pop star Ke$ha was also in the studio during the phone call from Styles, and she took the opportunity to divulge a secret crush on the singer, rating him a "10" for appearance and insisting he looks like "a young Mick Jagger".