Lanserhof-on the edge of the Tegernsee, which is an hour`s drive south of Munich-calls itself a medi-spa. By this it signals that, unlike your average pampering and preening resort, this is a stern, rigorous retreat dedicated to obliterating the results of unhealthy living. It opened in 2014, the newest in a group of three luxury German medi-spas, and it has won a fistful of awards from the travel industry. But it has more than gongs in its sights: It wants to change who you are. Although its clientele usually comes here to lose weight, Lanserhof`s medical director, Elke Benedetto-Reisch, says, "The main focus is to make people healthier. It is a cleansing, it is a regeneration, a re-creation of your metabolism."

This sounds uncomfortably ambitious. What would a re-created metabolism feel like? Still, the setting-a forested valley in the foothills of the Bavarian Alps-is peaceful enough. The main building, opened in 2014 and designed by Ingenhoven Architects as a series of low-rise rectangles set around a central courtyard, breathes tranquility, with slatted, wooden screens softening what would otherwise be rigorous expanses of window glass. It all makes for a soothing backdrop to the suffering that lies ahead.

I had filled in an extensive medical questionnaire before I arrived, so the staff had advance notice of the precise nature of my flaws. On day one, they plunged me into a series of examinations: urine tests, blood tests and measurements of my fat-to-muscle ratio. The results were not encouraging. Despite regular visits to the gym, I was told I was overweight and full of toxins. Plus, my body was retaining too much water, and my tongue was swollen. This was news to me-it seemed to fit my mouth rather comfortably.

The Lanserhof program is based on therapies developed at the turn of the 20th century by Dr. Franz Xaver Mayr, an Austrian holistic physician. Mayr believed that the key to human health is efficient digestion, and thus clinics such as Lanserhof base much of their programs on what they describe as "internal cleansing." According to Benedetto-Reisch, the "tongue, skin, face, eyes give us so much information about a person`s condition. I look at your tongue, and I know that your liver is overloaded." Blame too much salt and alcohol, eating large meals at night and not drinking enough water: All, apparently, had contributed to my unhealthy state.

So began five days of strict dieting, gym workouts, deep-tissue massages (the most effective I`ve had in a life full of massages, mainly because they didn`t hurt afterward) and frequent detox sessions. These almost undid me. Particularly day three`s "detox body-pack and bath." This started innocuously enough, with me-coated in a creamy goo that apparently contained three kinds of algae-lying in a hammock in a "micromolecular" steam bath. This would, I was told, accelerate the expulsion of toxins through my skin. As the day wore on, the headache I`d been suffering from for the past 24 hours grew more intense, and that night I felt so nauseated I barely slept. The medical staff assured me this was "great news:" It meant that my body was ridding itself of the toxins my decadent lifestyle had visited on me.

In between the detoxes and sparse meals-lunches of sheep`s milk yogurt and flatbread, dinners of very thin broth, eaten with a teaspoon-my long-standing gym habits were turned upside down by Ferdinand Bader, a 35-year-old former member of the German ski-jumping team. He said that the intense exercise regimes many of today`s busy executives swear by are both "dangerous and ineffective" for controlling weight.

"High-intensity training is nothing more than stress training," he told me. "So you have a high because you are releasing adrenaline and dopamine, and that leads to an increase in heart rate, blood pressure and muscle tension. And this usually takes place before or after a stressful day at the office, thus adding to the stress. The harder we exercise, the more carbohydrates and the less fat we burn."

With that, he outlined an exercise regime that he said would be more effective, recommending three gym sessions a week centered on cardio exercises and two on strength, all lasting longer, and at a lower intensity, than the short, high-intensity sessions I was used to.

On the fourth day-now largely recovered from my detox nausea-I was rewarded with a change of diet. Breakfast was a small portion of porridge and two boiled potatoes, each the size of a hen`s egg, followed by spelt bread and sheep`s cheese for lunch, and a dinner of chunky vegetable soup. Despite the tiny portions, I found myself unable to finish. My lunch companion was Peter, a British lawyer sent to Lanserhof by his wife to lose weight-a lot of weight. He announced, bleakly, that in the first few days he had lost just 4 pounds. "I`ve calculated that at this rate it`s going to cost me almost $200,000 to get down to size," he said.

My results were more impressive. On my final day, the scales showed that had I lost almost 9 pounds, my blood pressure had dropped by a good 25 mmHg- and my tongue was "no longer swollen." The medical director expressed great satisfaction at what she described as my "progress" and then handed me a checkout document that contained dietary, exercise and "mind and mental-health" recommendations for me. "If you had stayed for 10 days, I could have made you a new man," she said, "but if you follow the advice you`ve been given this week, you will continue improving."

To say that a week at Lanserhof changed my life would be excessive, but it`s certainly changed the most recent bit of it. Several months on, after continuing to follow the Lanserhof guidelines, my weight has fallen further, and my health is, touch wood, very good. So one of these days I might go back-if only to see if Peter the lawyer is still there.

Graham Boynton traveled as a guest of Healing Holidays and Lanserhof; the former (HealingHolidays.co.uk) offers a seven-day Lans Med Basic program at Lanserhof Tegernsee from $3,640 per person. This includes flights, transfers, accommodation in a double basic room on a full-board basis and all treatments as per the program.