When I announced to David, my long-suffering boyfriend, that I was staying at the Montreux Clinique La Prairie for a few days, he asked if I was going mad.

As a woman who hates being told what to do, dislikes most spa treatments, and definitely resents being put on a no-alcohol, healthy-eating regime, why would I want to expose myself to this? Fair question.

But it turns out preconceptions are not always accurate. I can’t promise that I am a total convert to the general spa experience, but Clinique La Prairie is not like other spas. This is serious. This is a health clinic. There’s no early-morning chanting, bathing in glacier waters, or being massaged with goat dung or whatever woo-woo suggestions some places come up with.

The modernized Clinique La Prairie still occupies the site of the original clinic, built on the banks of Lake Geneva in 1931. It has magnificent views of the Alps swooping down to the water, and in better weather, one could swim or sail. But I was there in cold, dank January, when the warm treatment rooms and lounges were more appealing.

Not that I lounged around much. Most clients spend at least a week there, but since my stay was to be for only three days, I was on a speed-dating regime, testing as many elements of the Longevity Program as possible. Exhausting, yes, but also interesting.

In my comfortable bedroom, I was thrilled to find wonderful old-school details such as plush furnishings and actual light switches rather than a mystifying computerized system. After a good night’s sleep, once I was awakened by a nurse arriving to take blood and urine samples, we got right to work.

Having recently had major abdominal surgery as part of my treatment for colon cancer, longevity has been on my mind. The experience and after-effects have taken their toll, but I found that the clinic’s emphasis on living better, not necessarily longer, made sense.

Clinique La Prairie is proud of its epigenetic testing, devised to examine in-depth aspects of one’s lifestyle that can help influence genetic modifications. This is deduced by a number of tests, such as an OligoScan analysis of mineral and trace elements, a detailed assessment of one’s eating habits, and a Huber assessment, to determine body strength and balance. (My right side is much weaker than my left, apparently.)

Since 1931, Clinique La Prairie has been at the vanguard of longevity.

Nutrition, exercise, muscle mass, body composition, and even sleep were all up for examination. And if you are a bit of a geek like me, you’ll enjoy poring over the many statistics they give you. Do I really have a metabolic age of 53, as my nutritional report suggested? (I’m 67.) I attribute this to bingeing on chickpeas from time to time. But before I got too pleased with myself, I discovered that despite claiming I do 180 minutes of exercise a week—it’s surely something like that—I was showing the results of someone who does only 60. Not so good.

Since I was there to review the experience, I was given some treatments I might not have chosen were it left up to me. A horrible session in a cryotherapy tank is definitely for only Silicon Valley tech bros. And I wasn’t crazy about spending 45 minutes in an infrared Vital Dome, a sauna that purportedly clears the body of toxins. But that’s me; others probably love it. Please do bring on the La Prairie facial, which is thoroughly indulgent—the skin-care version of the most delicious ice-cream sundae.

The rabbit warren of underground passages that connects the complex’s various areas—fitness center, medical center, Centre de Médecine Esthétique (should you want some tweakments while you’re there)—resembles something out of an early Bond film. If you’re looking for science, there’s no doubt that you’re in the right place.

So what did I learn? Well, my biological age is three months older than my real one, which is a win after recent surgery. I drink too much alcohol—who knew?—and my sleep is terrible. (And, frankly, their suggestions for improvement were very predictable.) I am also apparently super-tense and stressed. But my muscle mass is excellent, my blood is in peak form, and my general health is much better than I expected, including my fat mass (hurrah!) and cholesterol levels.

The clinic also has a detox regime with a more restrictive menu, but everything I tasted as part of the Longevity Program was light and delicious—even the oatmeal at breakfast. Coco-de-Paimpol-bean stew, edamame flan, and tonka-bean panna cotta are not on every spa menu, and they all had a marvelous intensity of flavor that compensated for the lack of starchy carbs.

Some people might prefer spending their precious away time being cosseted in fluffy robes, but I appreciated this investment in researching my body’s strengths and weaknesses. Now it’s up to me as to what I do about it. But then, as always, that’s another story.

Alexandra Shulman, the longest-serving editor of British Vogue, is a columnist at The Mail on Sunday and the author of the memoir Clothes … and Other Things That Matter