Diet is such a dirty word. At best a triumph of hope over experience, at worst a self-perpetuating industry based on failure - failure to be effective, healthy, sustainable - and the misery that results from this.
So why do we still get excited when we hear of something new? Something making familiar promises - lose weight, feel better - and then some? In the case of the 5:2 diet, devised by Dr Michael Mosley, these extra claims involve possible longevity, lowering of insulin, increase in healthy cholesterol and mental clarity, along with promises of long-term effectiveness; after all, the proof of a diet isn't the day you stop doing it, it's one year later when you track the lasting changes in lifestyle and body shape. A really successful diet is one that becomes a way of life.
We're excited because 5:2 might just be The One.
Briefly, 5:2 involves eating normally - as much as you want, whatever you want - for five days a week, and restricting to 500 calories for women, 600 for men, for the remaining two days. The recommended length is 12 weeks, after which you can drop down to 6:1 for maintenance. It's simple, without too much of the weighing of food and complex counting of calories that is so off-putting. Nor is it excessively penitential - visions of a carb-less life stretching ahead is deeply depressing -and it appeals to the kind of feast-or-famine mentality most of us have, plus that shred of common sense that tells us to follow a Sunday lunch blow-out with simple fare on a Monday.
Along with the diet, there is something called High Interval Training (HIT), which means bursts of intense exercise - flat out sprints for example - for just 30 seconds, followed by a couple of minutes recovery, repeated four or five times, meaning your entire workout is done in under 15 minutes. This, apparently, has weight-loss benefits that steady, longer runs, don't. The two combined are promising big things, something of a revolution in fact.
On the day I meet Dr Ray Power of The Well in the Beacon Clinic, he is waiting for the results of the first clinical trials to be conducted into 5:2 and HIT. These are being done in Ireland, at Dr Power's instigation, because of the chance that brought him together, during his time in Australia, with another GP who's best friend from medical school was Michael Mosley.
So why is Dr Power placing so much faith in 5:2? "The diet came out about two years ago, and I saw the original Horizon documentaries about it. Here at The Well, we liked what we saw, we wanted something to recommend to our patients, who aren't sick, but are keen to do the right thing. And so we approached Mike and suggested the first combined study. It hasn't been done before, and so we need to test the pudding. Is this really as good as it claims to be?"
And so a pilot involving 20 people has just finished, called IFAST12 (basically, Intermittent Fasting and Selective Training for 12 weeks). The final number-crunching by sports scientists isn't done, but "I did the 20 medicals myself, last week," says Dr Power, and "the impact has been brilliant." Of the 20 people, men and women, there were a range of ages and starting points - "some are really quite fit, others felt they needed to lose a bit of weight, most would have previously tried various other diets and regimes" - and every one of them showed significant benefit in terms of fat lost, waist-inches reduced and lower insulin. As did he.
"I've never done a diet in my life, and my weight is very stable. It crept up by a stone in the five years after I moved home from Australia, then stabilised and I haven't gained a pound in ten years. I run three times a week, for an hour, and it took me 16 weeks to complete the 12-week programme, because we went on holiday for three weeks in the middle of it." So, how did he fare? "I was thrilled, I couldn't believe how the combination of diet and training worked. I lost 7.5 kilos - which was actually 8kg of fat, and I put on 1/2 kg of muscle. Stopping for the three weeks didn't have a negative impact at all. I thought I'd find the fast days very hard - I eat a lot -and I thought I'd be grumpy, even light-headed, but no; I go to bed earlier, that's all. The first week is hard, then you adapt. I have a bounce in my stride, and I'm sleeping better."
As for why it works, there is plenty of science, but basically, "if you're taking in less calories two days a week, that has an effect. Interval training rather than walking or running actually reduces your appetite; you crave carbs less. This works because it's energising, and you feel good on the fast days. A 15-minute workout is time-efficient, so fitting it in is easier." It is, he stresses, "too early to call it, but the indicators are good."
In fact, so successful has the programme been for him that he is considering a major investment - getting his suits taken in to fit the new, improved body shape. "We are talking about this being a life-changing experience," he says, admitting that he is becoming quite "evangelical" about the possibilities. "The more I look at this, the more I think it has potential, beyond just one individual practice, even at a national level. The science is backing this up."
As part of the preparation for the 12 weeks, participants have a body scan, a heart check, blood tests and genetic profiling to see how well they respond to exercise. Based on results, the programme is then tweaked for each individual; "we are bringing sports scientists into this. We are working with Jamie Timmons, professor of Precision Medicine at King's College London. Each person gets a tailored programme."
So can you do 5:2 without the HIT, for the exercise-averse amongst us?
"Yes, but I worry a little about it in isolation, because if someone is just doing the fasting, they might be losing weight, but not the right type of weight."
Could you avoid the expense of blood tests and genetic profiling, and just launch into it? "Yes, again, but it is more successful and sensible to do it monitored. However, that can mean a simple trip to the GP."
He would also like to bring mindfulness into it, because he believes there is a psychological benefit beyond the joy of feeling fitter and lighter. "As for psychological well-being, we are not designed to be in go-go-go mode all the time, with cortisol and adrenalin on overdrive. That's not good. We need to slow down sometimes."
But, we have been here before - the brave new frontier of diets-to-end-all-diets. Is it possible this will turn out not to be all its cracked up to be? Either because it doesn't work long-term, no one can stick it after the initial weeks, or because it has adverse side effects? "It is critical from our side that we don't do anyone any harm. That's why, although there is no commercial requirement to be hooking in with academics, we still do it. A lot of work is being done around calorie-restriction and interval training - proper, peer-reviewed material - and there are now huge databases of patients who have been tracked for a number of years, and the research is saying the opposite. That intermittent fasting and interval training have a good impact on overall, long-term well-being."
So what's next? "To keep tracking the ones we have and repeat the body scan after a year, and ramp up the trial, to 200 people. We need proper academic studies, then we put a White Paper together and present that to government. I will be knocking on the door of the Oireachtas. I think that at a national level, we need to be embracing an approach like this. I would see the whole country doing it. I would have a vision where communities come out together and get fit, their self-esteem and sense of achievement improve."