Discussing one's diet with Dr Michael Mosley, journalist and medic, feels a bit like confessing directly to God. Michael may not claim to have created the world in seven days, but this is the man who carved that week up into two healthy portions, to invent the most popular diet this century: the 5:2 (or 'Fast') Diet.
This is the eating plan that has seen people up and down the country shed pounds of weight and shrink inches without the need to quit their white wine or Ferrero Rocher habits, as long as they keep their calorie intake below 500 cal (600 for a man) on two days a week. Indeed, it has taken the world by storm: celebrities from actress Jennifer Aniston to model Miranda Kerr – and TV presenter Phillip Schofield – are reportedly fans of intermittent fasting.
So when I sit with God – I mean, Michael – and talk about what I eat every day, it is with some trepidation. He's handsome, slim, offers dispensation on doughnuts, and emanates the sort of twinkly joie de vivre that makes you long to become a disciple.
Which is just as well as, from this meeting, I am officially joining Michael's devotees to test-drive the latest offering built on his research: the Fast Beach Diet, a ramped-up version written engagingly (like the original) with Michael by the style journalist, Mimi Spencer.
The Fast Beach Diet promises a 12lb weight loss in six weeks if you closely follow the 5:2 principles while tightening up your eating on non-fast days – and adding a bit of exercise, too.
And we need this harder, faster version of 5:2, because Michael and Mimi may be supreme beings, but they can't work miracles. This is the diet to try, I'm told, when your weight loss has slowed down, or you suddenly remember that 30th anniversary or school reunion. Or, worse still, you've realised it is only six weeks to that summer holiday booked back in January, when we were all living in voluminous waterproofs.
But before I open up to Michael over black coffee about my fat ratios and preferred sandwich fillings, I ask him if the diet, which he has now been following for 18 months, is still that easy.
"The annoying thing about humans," he tells me, "is that we're really good at retaining fat. So before I discovered the benefits of eating like this – what is known as intermittent fasting –I knew I needed to lose a few pounds (at 5ft 11in, he weighed 14 stone), but my efforts to lose them were pretty vague and never lasted." But then Michael, who produces and presents award-winning programmes on science for BBC Two's Horizon, started to explore the science around fasting, and whether it could help us live longer and actively improve our health. He was particularly impressed by the research that linked intermittent fasting to a reduction in the risk of diabetes and dementia – both conditions from which his late father had suffered, and which, consequently, he feared.
Michael began fasting two days a week – "every other day was too difficult" – and by the time the television programme aired in 2012, he had lost 18lb, mostly of fat, not muscle. But that wasn't all: his blood sugar, which had suggested he was close to developing diabetes, had fallen to normal levels; his fat percentage had dropped from 28pc to 2pc. He even measured a blood protein called IGF (insulin-like growth factor 1) which can predict cancer risk: his had fallen from high to low.
"I was jolly pleased," he says, charmingly understated.
Best of all, Michael says he is proof that this is the diet that anyone can keep to. Eighteen months in, he fasts a couple of times a week. He adds a few sessions of High Intensity Training (HIT) – an exercise regime that also grew out of a Horizon show into a book called Fast Exercise, where you aim to raise your heart rate with two bursts of exercise for just 20 seconds, at maximum effort, three times a week. HIT, research shows, seems to burn fat more efficiently than the universal standard of 30-minute sessions five times a week.
"It'll be a quick sprint when I can," says Michael, "or just running hard up the stairs.'' He really is the model of attainable, sustainable health.
Michael, Michael, where do I start?
"The 5:2 is not a prescriptive diet," he says. "Everyone has to find their own way to stick to it. That could mean two fast days in a row, or more intensely fasting 3:4 some weeks. Some people like to eat a boiled egg in the morning'' – sans soldiers, of course – "others go through the day on black coffee and lots of water until early evening when they spend all their calories on one meal. Experiment till you find what works for you.''
He advises that I tot up my calories using an app such as MyFitnessPal – there will soon be a Fast Diet app, too – and that I make grown-up choices on the non-fast day, taking care to avoid what he calls "50:50 foods" – those that are, broadly speaking, half fat and half sugar, such as muffins or chocolate bars.