According to the BBC, Zayn wrote he would go days without eating, sometimes skipping meals for two to three days straight.
"I'd just go for days - sometimes two or three days straight - without eating anything at all," he wrote. "It got quite serious, although at the time I didn't recognise it for what it was."
The 23-year-old says that his condition was at its worst right before his final tour with former band One Direction and it wasn't till after he left that he came to terms with his eating disorder.
“When I look back at the images of myself from around November 2014, before the final tour, I can see how ill I was. Something I’ve never talked about in public before, but which I have come to terms with since leaving the band, is that I was suffering from an eating disorder.”
“I didn’t feel like I had control over anything else in my life, but food was something I could control, so I did,” Zayn wrote. “I had lost so much weight I had become ill. The workload and the pace of life on the road put together with the pressures and strains of everything going on within the band had badly affected my eating habits."
It wasn't his weight that Zayn was concerned about, but his life. He wrote that he felt so out of control that eating was the only thing he could control.
“It was just more down to losing track of, you know, actually eating, and being super busy and getting caught up with other things that 17- or 18-year-olds do, which normally entails them going out, drinking or partying.”
Though, he was never diagnosed with an eating disorder, he added, that he is better at managing his diet now.