11/27/2007 at 07:00 AM EST
Lily Allen says she has lost almost 20 lbs. since August, when doctors detected a heart murmur during a routine examination.
"I have been asthmatic all my life," Allen – who has publicly battled weight issues
in the past – said in the new edition of Britain's Grazia
magazine. "But this was really quite scary."
Since the diagnosis, the 22-year-old "Smile" singer said she has stuck to an exercise regimen, including at least three one-hour gym workouts per week. And Allen says the discovery also triggered a major diet overhaul.
"I used to love nothing more than sitting in front of the telly with two packets of ginger nut [cookies] and two bags of milk bottle [candies] – and I'd devour the lot," she told the magazine at the launch of Chloe's Spring 2008 collection in London. "But this heart thing has made me cut back on all that."
The British singer is also limiting her alcohol consumption. "I was going pretty crazy back in the summer, drinking way too much and partying loads," she explained. "I've been cutting back."