Holidays used to be about lazing and lotus-eating, sun-dappled indulgence, not subsisting on calorie-free broth in a gale.

But vacations are now opportunities for the beau monde to become more beau well away from the monde, under the scrutiny of an army of medics. Why check out to paradise when you can check in to the doctor, full-time, for a week, argue these high-net-worth puritans.

The Lanserhof clinic on the island of Sylt is the place for them. But is it the place for me? Sylt (pronounced “zult”) is known as the Hamptons of Germany, somewhat optimistically, given its North Sea locale. Popularized by playboy Gunter Sachs and his second wife, Brigitte Bardot, it is home to the soccer world’s jet set. Bijou branches of Cartier and Hermès, five-star hotels, and the very finest fine dining fill its main streets. Only I wouldn’t be experiencing this, because I would be breaking fermented buckwheat bread at Lanserhof.

My goal is to possess more energy. I cannot blame long covid for my entire lack. Instead, at 53, I could fall asleep at any hour of the day—not so much the worried well as the walking dead. The Lanserhof resorts—this, along with ones in the Austrian Tyrol and on a German lake—make gut health their focus. It is an obsession once scorned as irredeemably German, now fashionably regarded as the engine of health.

Friends learning of my trip responded: “The fat camp that’s all hemp shirts and chewing?” In fact, it’s a longevity camp that’s all Loro Piana cashmere and chewing. A cow going at a cud-like 40 grinds per mouthful, overseen by a mastication mistress in otherwise silent meals. I arrived at the austerely beautiful stone-concrete-and-wood structure to a church-like hush. Lanserhof is topped by the largest thatched roof in Europe. Every guest room is a two-story suite, flooded with light and calm.

Why check out to paradise when you can check in to the doctor, full-time, for a week?

I’m handed blue Birkenstocks and instructions to read the 40-page treatment list by morning, followed by a 157-page treatise on the gut. After a supper of fennel soup, it’s straight into a lecture on autophagy, a cellular cleaning process—which occurs when the body is deprived of nutrients—that sheds dead “zombie” cells. “Zombie,” I sigh, feeling seen. The Lanserhof “cure” is the path to autophagy, and the staff speaks about it as if it’s a form of enlightenment.

And by “cure” they mean fasting, intermittent or full-on; plant-based, simple meals (with nothing raw after four P.M., when it’s too challenging for the digestive system); no alcohol or caffeine; no liquids with, or immediately before, food; eating interminably slowly; the chewing and chewing; and cleansing of the bowels via Epsom-salt-spurred eruptions. Digital fasting is also required; diners conceal their phones under napkins.

At Lanserhof, everything from the rounded staircase to the tiled steam room is designed to soothe and cocoon.

I spent my first morning in an array of medical exams: blood-pressure, muscle-mass, B.M.I., nutrient, blood-sugar, cholesterol, urine, and breathing-efficiency tests, plus a psychological evaluation. After a mere 10 minutes, my medical supervisor deemed me “too sad and tired” for starvation. She granted me 750 calories a day, building up to a lavish 850, consisting mostly of sheep’s-milk yogurt, cooked carrots, and wheatgrass.

I missed crunch and quickly started fantasizing about apples. Taking my “evening meal”—a thimble of soup—at 5:30 P.M. marked the destruction of all that is civilized. Still, according to Lanserhof lore, it is civilization that is destroying us, so I buckled down.

My test results were mixed. Bizarrely, given I do not exercise, I emerged as strikingly fit, my blood bursting with nutrients, and even boasting muscle. Less positively, I discovered I absorb so little oxygen when I breathe, I’m barely alive. Maybe this, at last, explains my enervated state.

After studying my nervous system, and asking a lot of questions, my psychologist also diagnosed me not as depressed, which is how I regard myself, but traumatized. Dreams of violence and regularly dissociating are not, apparently, the human condition.

My medical team supplied breath training and psychotherapy sessions. Lanserhof also offers cancer screenings, colonic irrigation, dentistry, and bone-density scans. Or why not sneak into the aesthetics zone and indulge in a thread lift you can pretend, on return, to be among the miraculous effects of fasting?

Perhaps that’s too invasive. As alternatives, there are workouts with a trainer, beach walks, cycle excursions, steam, sauna, massage, cooking classes, screenings of Eugene Levy visiting the Lanserhof for his Reluctant Traveler series, lectures about urology, a cello recital, or, in my case, strenuous napping.

The people-watching was sublime. In the lounge, collapsed on my Eames chair, I studied the craggy old men, all starvation-raged; seal-sleek C.E.O.’s; middle-aged gal pals and icy fashionistas. An arriviste clan bonded in the smoking zone, three generations of Kelly bags and significant watches. The couples were particularly fascinating: hand-holding their way to bed, clutching trays of Epsom salts.

By day six, I was hungry, yet curiously energized, possibly actually respiring. Immortality assured, I was in a buoyant mood, greeting my “Sunday roast” of tofu, scant vegetable matter, plus a nipple-size portion of goat’s curd with actual mirth. I caught my spa pal, Ned, a London barrister, after he had dropped $6,000 on treatments on top of the $6,000 he paid to attend. “So would you do this again?” I asked. “I’m already signed up!” he cried, having shed seven pounds.

I, too, am sold. Lanserhof Sylt was a life-restoring Prospero’s island: the thousand twanging instruments replaced by a concert cello, the sweet airs filled with keto breath, its interlopers chomping their way to redemption. As for the sea change, it lasts. Four months later, Ned tells me he’s lost another 21 pounds, while I qualify as almost human.

Hannah Betts is a features writer and columnist at The Times of London and The Daily Telegraph