The statuesque Englishman is by no means on some kind of diet. He's actually on the Los Angeles Fox studio set of anthropological series Bones, playing quirky police psychiatrist Dr Gordon Wyatt.
"Cut," shouts the director. "Can someone cut up the salad a bit?"
Stephen says he enjoyed his Bones experience the first time that it was easy to reprise his role for an episode of the drama which revolves around the investigations of anthropologist Dr Temperance 'Bones' Brennan (Emily Deschanel) and Special Agent Seeley Booth (David Boreanaz).
In this episode, the first since Stephen played the character in season two, Wyatt turns up to announce his retirement to Bones and Booth. However, he ends up sticking around to help investigate the disappearance of a black metal band member after it emerges Wyatt was in a glam rock band in his youth.
In reality, it's hard to imagine a more unlikely black metal rocker.
Stephen, dressed in Wyatt's eccentric professor gear complete with red waistcoat and slightly untidy hair, admits his teen tastes in music were more Wagner, Beethoven and Mozart than Black Sabbath.
"Between Emos, Goths and metal heads, I was aware I couldn't read the code," the 51-year-old admits, cradling a cup of coffee in the deserted Founding Fathers bar on the Bones set.
"They're usually very sweet underneath. But they look like some sort of wet dream of Himmler's."
Glam rock aside, Wyatt's mental agility, eloquence and quirkiness make him a bit of a dead ringer for Stephen himself.
"That's the nature of casting isn't it?" he muses.
"The best parts are the ones closest to you. Then you don't have to act. And acting is so horrible when it's visible on screen. It just gets in the way. No one likes to see acting. Was it James Stewart who said 'you find the part of the character like you and take all the rest of you away'? That's why these great film stars are so authentic. You don't catch them acting."
Bones is a brief respite in the life of Stephen Fry, actor, presenter, author and well-known web user.
Los Angeles happened to be a convenient stopping point between jobs in New Zealand and Mexico where he is filming Last Chance To See, a BBC series on endangered species.
After filming finishes on Bones he's off to Mexico to see the endangered blue whale, but when we meet he is clearly enjoying his two weeks in Hollywood.
Last year he visited every US state for documentary series Stephen Fry In America - and hasn't ruled out moving there permanently.
"It's a wonderful country," he says.
"It's fabulous working here. This is an extraordinary machine, American drama and episodic TV."
But all this travelling means he is often away from his family and partner of more than 10 years, Daniel Cohen, whom he lives with in Norfolk and west London.
"It's tricky for my partner and for my parents as well, who like to see me from time to time," he says.
"Over the last two years in particular, I've hardly spent a night in England, what with one thing and another. But I'll go back in the middle of April and there's the QI programmes, so I'll be more settled for a while."
Being in California, talk turns to Proposition 8, and the banning of gay marriage, which the state voted in favour of last year.
Stephen says he's "never quite seen the point" of marriage.
"It's good that you can and I'm happy. But so sad, Prop 8. It doesn't matter to me if you want to use the word marriage. If people want to reserve marriage for a man-woman thing then fine, call it something else. A bonding, a uniting, a legal yoking - that's fine. Yoking is a lovely word," he says happily. "Yoked together..."
As Stephen is called away to do another take of the fiddly lettuce-eating cafe scene, his old friend Hugh Laurie, based in the States for hit medical series House, arrives and the pair give each other a hug.
Hugh doesn't stay to watch filming, but Stephen says he sees his old comedy partner "all the time" when in Hollywood.
Later this year Stephen will begin writing the second part of his autobiography, which promises to cover his university years and the Cambridge Footlights drama group where he met the likes of Hugh, Emma Thompson and Tony Slattery.
"I'll maybe do the whole of the autumn in Norfolk writing," he says.
"It's something I haven't yet grappled with. There is pressure. It's different because the first volume (Moab Is My Washpot) was a private memoir of childhood. It didn't involve having to put in people who have now become well known. The trouble with it now, is the moment it starts, it would have to be at university and it would be Hugh and Emma and all that sort of thing. It becomes a showbiz biography and I'm keen for it not to be too much. Why would I want to involve people without their permission?"
Despite being able to wax lyrical on a number of subjects with great wit and eloquence - as seen on the irreverent BBC Two quiz show QI, Stephen is a private man and does not enjoy interviews or seem to particularly like the press.
Maybe he's got good reason, considering a few unfavourable headlines following his 1995 breakdown when he absconded from West End play Cell Mates. He has since been diagnosed with a form of bipolar disorder, which he discussed during his 2006 documentary The Secret Life Of The Manic Depressive.
Instead of interviews, this technology enthusiast prefers using social networking service Twitter - where he has more than 340,000 'followers'.
"It means I don't have to do this kind of thing, and you can't put a price on that," he says.
"I've always been very interested in digital technology. No one quite understands what the point of it is and how it works but it's enjoyable. It's probably less enjoyable the more you talk about it - that's the problem. It interests the press enormously because they get free gifts of information from people they're interested in. On the other hand it terrifies them that it cuts them out of the loop.
"Suddenly people are talking to their own fans. I don't use it for that," he adds, hastily.
"I don't have fans in the way a musician might."
Stephen Fry - Extra Time
Stephen Fry was born on August 24, 1957 in Hampstead, north London.
Playing Oscar Wilde in 1997 film Wilde earned him a Best Actor Golden Globe nomination.
He supports Norwich City FC.
Charles Dickens, Arthur Conan Doyle and C.S. Lewis are some of his major influences.
He is modest about his intelligence.
"People are very sweet to cede to me this apparent intelligence. I would grant certain things. I've been given big feet and a big memory. And memory is an incredibly important thing."