Winehouse said that the "Rehab" singer began purging at the age of 17 with a group of friends.
"They'd put loads of rich sauces on their food, scarf it down and throw it up," Winehouse said. "They stopped doing it, but Amy never really did...We all knew she was doing it, but it's almost impossible [to tackle] especially if you're not talking about it. It's a real dark, dark issue."
"She suffered from bulimia very badly," he continued. "That's not, like, a revelation—you knew just by looking at her...She would have died eventually, the way she was going, but what really killed her was the bulimia...Absolutely terrible."
According to Winehouse, had his sister not had an eating disorder she would've been "physically stronger."
"All she wanted to be was a singer and have a good career and that was it really," he added. "[The attention] was slightly out of whack with what she was. She won the Brit in 2007 and no one knew who she was before that. I remember bumping into her on the tube once and she was on her own. Then, all of a sudden, that was it. In the space of one evening she'd gone from being able to do whatever she wanted to not being able to do that ever again."
Winehouse attributed his sister's alcohol abuse to a way of coping with the pressure of being famous.
"The problem with being [famous] is -- how many people tell you 'No'? No one does," he said.
Asked about what the "Back to Black" singer would've said about the media attention that ensued her death he said "she would have hated it."
"She would have been…" He assumes her voice, high-pitched and bemused: "'It's just me, why do you want an exhibition?'"
For Alex Winehouse's entire interview visit The Guardian.co.uk.