The 800-calorie fast that promises to shift the pounds in 5 days

Sometime last year, largely in the name of vanity – a highly motivational tool, don’t knock it – I tried out an 800-1,100-calorie-a-day mail-delivered ‘fast’ diet called ProLon.

Eight hundred calories isn’t a lot (although since when did a fast have any calories?), but it happens to be the same amount as the meal-replacement diet that the NHS recently announced it would be prescribing to type-2 diabetics, following some promising results in its trials, which saw both weight and insulin levels plummet.

I needed every last ounce of motivation when my five days of ProLon first arrived in a box the size of a medium handbag. ‘Where’s the rest?’ I asked Kim Pearson, the down-to-earth nutritionist overseeing me. ‘What rest?’ she replied.

I circled the derisory amount of soup packets, nut bars, seaweed crackers and herbal teas for a few weeks, waiting for ‘the right moment’ (i.e a week when I had run out of excuses for not doing it), and guess what? Things weren’t as terrible as I’d anticipated.

I can’t claim it was as much fun as five days of Christmas comfort food... but then again, the results were infinitely more satisfying.  There’s a lot of science testifying as to why this constitutes a ‘fast’: the bottom line is that, despite the low calories, it provides balanced nutrients for a fiveday kick-start blast.

Devised by Dr Valter Longo PhD, an American biogerontologist, it is – here’s the sales hook – designed to work on the body the same way an intermittent fast would.  Who understands, apart from Dr Longo, how this actually works?

What we do seem to know (or, at least, most nutritionists agree to be the case) is that when you fast intermittently – either the 5:2 (sticking to 500 calories, two days a week), the 16:8 (consuming all your calories within an eight-hour period out of every 24) or variations thereof – the body benefits. Weight drops off, digestion improves, fat-burning increases, cholesterol decreases, mental clarity improves... and so it goes.

I have to say, I’ve never seen any of these benefits on the 16:8 (and each time I tried the 5:2, I would wake up at 3am ravenous). But on the ProLon eating plan, I didn’t have these problems.

Yes, I was peckish on day four and five. Yes, there are a lot of powders – all a bit space age, and not my usual MO (which is to eat healthy, home-cooked organic food). And it’s not exactly cheap (￡225 for five days). But it’s cheaper and more convenient than schlepping to a spa for the week,  and all the thinking’s done for you.

After five days, I’d lost 2.5lb. My IGF-1 (insulin-like growth factor), which findings at Longo’s research centre suggest may be a precurser to cancer in adults, dropped, while my bad cholesterol also reduced from slightly high (3.3) to 3 (within acceptable limits).

For optimal results you’re meant to follow the plan three times in three months; thereafter, three times a year. Weight-wise, it won’t work as a sustainable strategy if you go straight back to your old ways, but it can be a very helpful reset tool.