Zayn Malik has reportedly lost a lot of weight due to stress.

The One Direction star, who is dating Little Mix member Perry Edwards, has recently dropped a few pounds because of his busy schedule and allegedly hasn't had time to take care of himself.

A source told UsMagazine.com: ''He's lost a lot of weight. He started to eat healthy a while ago and working out to get in shape as he had never trained before. He wanted some definition.

''He's always been the slimmest of the band members, naturally, but I think he's running around a lot, getting stressed, and not putting health first.''

The 20-year-old 'Kiss You' hitmaker kicked of the U.S. leg of the boy band's Take Me Home world tour on Thursday (13.06.13) and will perform 35 shows across North America over the next three months.

The band, which also includes Harry Styles, Liam Payne, Niall Horan and Louis Tomlinson, are also busy shooting a new video and doing promotional appearances ahead of the release of their debut movie, 'This Is Us 3D', which will be released in August.