If someone offered you the chance to lose up to a stone in ten days, perched on the edge of dreamy Lake Constance in Germany, interspersed with beautiful walks through pine forests and restorative massages, naturally you would ask where the catch was.

There’s no such thing as a free lunch after all. Well, the catch is there is no lunch at all. And no supper either. The price of this bliss is to live – virtuously – off 250 calories a day. And it’s not as tough as it sounds.

I had a ‘Dad bod’ way before they were a thing, and the quest for the sort of body that would make me happy found me in many a famous spa across Europe and as far away as Thailand. And then a friend told me about Buchinger Wilhelmi, a family-run fasting clinic based in southern Germany with a second newer branch in Marbella.

Fasting is as old as time, a cornerstone of most religions, and very now. So now, in fact, that it’s become less a diet, more a lifestyle that’s slipped into the daily consciousness of people who know a thing or two about fitness and nutrition. The 5:2 is the most well-known iteration (the 5 referring to the days you eat as per, leaving two days a week where you vastly restrict your calories, usually to 600 or less. It’s much easier than it sounds), Hugh Jackman does the daily 16:8 (the 8 referring to the window of hours you can eat, the 16 being the bit where you’re nill-by-mouth. It’s also much easier than it sounds), and Dr Michael Moseley off the telly has written very good books about it.

The principles are simple, though the science complex. Cut down your calorific intake to the very minimum necessary for survival and your body will first consume the glucose we all store naturally to provide energy, then it starts to cannibalise the body fat that lies around your organs and finally – and this is the time to slow the fasting – it turns to your muscle mass. At Buchinger Wilhelmi, your calories come from vegetable broths or fresh fruit juice twice a day, washed down with at least three litres of water and a dizzying array of herb teas on 24-hour tap. Yum, right?

The surprising bit is that your energy levels increase dramatically. Sure, you’ll get the standard caffeine deprivation headache on day one, the urge to kill anyone who crosses your path on day two but, after that, you slip into a kind of zen. Your every step is monitored by kindly nurses and there is a full medical examination at the beginning and end of your stay. In between, after a morning weigh-in, your days are fit-to-bursting with massages, walking, yoga, meditation, lectures, more massages – basically, the lovely stuff to lower your blood pressure and cortisol (stress hormones) levels. After a few days you begin to wonder how – and why – you ever wasted so much time actually eating.

There are of a few downsides, particularly if you’re a first timer. Your sleep patterns are usually broken – most people go to bed around 7 or 8pm and wake very early. I find I wake a lot in the night (an obvious side effect of drinking so much during the day) and when I do sleep my dreams are extravagantly wild with food fantasies becoming almost erotic. But I averaged eight hours end-to-end which I rarely do back home.

Buchinger Wilhelmi isn’t as fancy as the superstar spas of late – Lanserhof, for example – but it’s more geared towards the serious faster. The rooms are very comfortable, each one with a balcony looking out over the lake. You are not supposed to take any digital device out of you room, both for yours and the other guests’ wellbeing, but I noticed several addicts sneaking peeks in quiet corners. Bad people!

And the therapists are standout; their sports massage team is pretty much the best I’ve ever experienced, Siegfried Kaiser-Schropfe a superstar osteopath who uses tiny movements with just his fingertips and assesses the imbalances in your muscular-skeletal structure and realigns it. Which is smart, right? Next door, Tomas Lutz, another Buchinger Wilhelmi veteran, does a Shiatsu massage using tuning forks on your spine, and it’s almost hallucinogenic. If you’re going, book sessions with them well before you get there as the queue for their magic is long. For the gym bunnies among us, there’s a hall packed with brand new equipment looking out over the lake and manned by trainers who’ll create a programme for you should you be inclined. I topped up all of the above with infusions of re-oxygenated and ozone treated blood (my own!), followed by massive doses of intravenous Vitamins B and C.

At the end of your fast, you are eased back into the real world with a couple of ‘re-feeding’ days of 800 calories. The vegetarian meals prepared by Herr Hoehler, their chef of 30 years, will make you reconsider your meat eating habits if you ever had them. Sensational flavours using vegetables and fruit that are all grown locally, many of them especially for the clinic.

I’ve never left Buchinger Wilhelmi less than a stone lighter and with lower blood sugar and stress levels. ‘Fast mourning’ is a common phenomenon once you leave this place. It turns out that the proof of the pudding really is in not actually eating it!

10-day fasting programmes from £2,340 per person including two consultations with a doctor, daily nurse check-ups, all food/beverage fasting provisions, and daily activities. Other longer and shorter packages are available.

Buchinger Wilhelmi has also just launched its Immunity+ Programme, which aims to strengthen both body and mind, with the specific target of reducing the main risk factors for severe cases of coronavirus and chronic disease (such as obesity, cardiovascular diseases, diabetes, liver disorders), and to boost the immune system.

For more information, visit buchinger-wilhelmi.com or call +49 7551 8070.