The comedian was looking trim and happy on the red carpet in Hollywood ahead of hosting Bafta LA's Britannia Awards.
The QI presenter said: "I have been on a diet of my own devising and exercise, I go to the gym every morning - I saw myself in a mirror almost exactly a year ago, it was November 2008, and I saw this gigantic walrus crossing the room through the mirror and I thought 'that can't be me can it?' and it was and I thought it's got to stop."
In total the star has shed six stone since deciding to lose the weight.
"For the first time I took it slowly. In the past I'd gone on crash diets that worked and then I hated them, this time I just sort of eased my way in to a different way of eating so that sort of worked," he explained.