Rebel Wilson lost eight pounds.

This is the legend at a certain luxury boot camp in Malibu, California, where celebrities and the wealthy drop in for long weekends of brutal exercise and just enough food deprivation to feel ecstatically light-headed. The program, which involves hours-long, vomit-inducing hikes and vegan, gluten-free food, promises “sustainable results” in four days. It is called “the Ranch 4.0,” and it costs $4,100. Thanks to Instagram, it is now one of the most popular torture chambers of its kind.

In recent months, Mandy Moore, Minka Kelly, Connie Britton, Lea Michele, Julianne Hough, and Selma Blair have all posted photos of themselves sweating victoriously on the Ranch’s resplendent trails. “I wish I could stay here longer,” Blair raved. “Nothing like hiking 14 miles a day to the top of a mountain!” Michele gushed. “I lost 8 pounds from marathon hiking … Feeling great!!” Wilson reported, topping them all.

The Ranch advertises its program as having “no options.” Trainers wake guests at 5:30 each day, literally walk them through four-hour hikes, and serve them no more than six almonds on the trail. This is the new wellness, where deprivation is luxury, choice is eliminated, the environment is completely controlled, manicured hands are held, and transformation — being bought and paid for — is all but ensured.

The Ranch is by no means an outlier in this regard: The “wellness tourism” industry has exploded in recent years, expanding from $438 billion to $494 billion in revenue from 2012 to 2013. Deprivation programs like the New Life Hiking Spa dominated Travel + Leisure’s top-ten list of destination spas in the U.S. this year. (The Ranch came in at No. 3.) And even at home, there are now fitness concierges to physically rouse you and drive you to SoulCycle. Does it still count as willpower if you pay someone to make you do the stuff you know you should do but probably wouldn’t if truly left to your own devices?

One weekend in June, I decided to find out. I took a plane to Los Angeles and a $147 cab ride to Malibu to hike among celebrities and the noncelebrities who actually pay for this kind of thing. Against all better judgment, I too felt drawn to the promise of a luxurious bodily asceticism. Though I have no interest in exercise as a daily or even weekly practice and consume mac ’n’ cheese more days than not, I imagined myself returning from California five pounds lighter, gleaming with superiority and a newfound love of raw vegetables.

The horrors began before I even set foot on the grounds. Ten days before I arrived at camp, I received an email from the reservations coordinator. Already the Ranch was trying to take over my life. To prepare for the detox to come, she recommended I eliminate processed foods, sugar, artificial sweeteners, caffeinated beverages, decaffeinated beverages, and alcohol from my diet. (And gum!) If I didn’t stop consuming those items before the program, the coordinator warned, my stay at the Ranch would be “quite uncomfortable,” and I would likely fall victim to “headaches, nausea, and extreme moodiness.”

Also included in the email was a list of items that would be considered contraband at camp (“DO NOT PACK”). The list was similar to the do-not-eat list, with one notable addition: matches. Extremely moody people should not have access to matches, I guess.

I wasn’t prepared for this kind of intrusion into my pre-Ranch life, but I had signed up for someone to tell me what to do. So I gave up coffee (horrific) and wine (a shame), but not “processed foods” or anything else (that hell would come soon enough). I packed up special hiking shoes and a backpack with a water pouch in it and no matches. When I landed at LAX the morning of the first day of camp, I bought a chocolate-chip granola bar at Hudson News and hid it deep in my suitcase, just in case.

The first thing I notice when I arrive is that none of the other guests look like they need to lose weight.

I recognize a tall, handsome actor from his run on Girls and a bleached-blonde, 50-something publicist who happens to be the alleged ex-mistress of a famous billionaire.

Then there’s a lean, wiry middle-aged mother from Houston, a petite fashion designer from Paris, and a spry brunette pet-food entrepreneur from perhaps another planet. She does not participate in most of the program, choosing instead to emerge, suddenly, at various intervals throughout the weekend, mostly when food is being served. She has manipulated her features in such a way that it is impossible to tell whether she is 40 or 60.

There’s also a rosy, round-faced tech worker from Boston who later reveals that she recently quit her job to focus on her weight-loss goals full time. And an entire family of four from San Francisco: a mother, a father, and two 20-something daughters, the older of whom is getting married in the fall. At separate points in the trip, each family member tells me it was another family member’s idea to come here, to prepare for the wedding. “Oh, my mom researched it all,” says the bride-to-be. “Oh, the girls thought it would be neat,” says the dad. Maybe they all want to be here, or maybe none of them do.

Photo: Courtesy of The Ranch at Live Oak Malibu for PR

“This is much nicer than the Ashram,” a barrel-chested “serial entrepreneur” just on the edge of 40 tells me as we fill out our paperwork releasing the Ranch from liability in the event of our untimely deaths. He’s here because things got a little crazy at BottleRock in Napa last weekend, and he needs to hit that “reset button.” I tell him I’m here to review the program for a magazine, and he rushes to explain why the Ranch 4.0 is better than all the other expensive boot camps out there (he’s done a few).

In short, it’s fancier. The nearby hiking retreat the Ashram, he tells me, is a real camp, with shared bunks and showers and no cell reception. “It’s basically in some old lady’s house,” he explains. The Ranch 4.0 is housed, much preferably, within a Four Seasons hotel near Malibu. Later, we will be shown to our private, plush rooms, which have deep marble soaking tubs, flat-screen TVs in the bedrooms and bathrooms, and, crucially for celebrities and other people who like to Instagram themselves five times per day, WiFi. (Due to the terrifying, concurrent rise of social media and “wellness” culture, celebrities no longer have to hide a visit to a weight-loss retreat. For the almost-A-list, lifestyle-oriented actress, a Ranch 4.0 Instagram is a badge of honor — it signifies that the star in question is either famous enough to attend for free or so successful that she can afford the best.)

The Ranch merely offers the option to “unplug,” a general vibe of unpluggedness, without any kind of potentially unpleasant mandate to do so. To get the full experience, guests could try visiting the Ranch’s original private property in Malibu, which is home to more intense weeklong programs. The Ranch 4.0 is for “guests desiring a jump-start to a healthier lifestyle who are unable to be away from home or work for a full week and who desire to maintain more connectivity during their program immersion.”

When we go around the room to introduce ourselves, nobody lets go of their phones.

The program itself ranges from extremely scientific to what you might lovingly call “hippy dippy.” On one day, we have the option to visit with an “energy healer” (for an extra charge), but on another, we take turns climbing into a submarine-style pod that somehow determines your body composition by shooting a blast of air at you. (The pod reveals that I have 31 pounds of body fat, which I think is rude.) Then, of course, there’s the endless hiking. If I had to come up with a mission statement for the Ranch, it would be: Whatever It Fucking Takes. The actual mission statement is much longer and contains the words sacred, calibrated, and regime.

The first test on our journey is one of endurance. After completing our paperwork, all 12 of us march downstairs to the basement level of the hotel and take up uneasy residence in its steely gym. A tall, almost comically sexy Ranch trainer named Matt greets us and explains the test: We will each take turns running on a treadmill until we feel like we can’t anymore.

When it is my turn, Matt asks me to lift up my tank top so he can attach a heart-rate monitor to my magenta sports bra. I comply, doing my best to harden my pale, soft stomach by not breathing.

“There,” he says, in a deep, Southern California rasp, as he clips the monitor into place. With his dark, swoopy hair and blue-green eyes, he looks instantly familiar and sort of famous in a way I can’t place. Perhaps he went on a date with Lauren Conrad on The Hills? Maybe he was on The Bachelor?

I don’t have time to think about it, because the treadmill is starting. I last for a number of minutes that earns me a praiseful “okay” from Matt.

Later, a fellow camper tells me that Matt is Matthew Paetz, the recent ex-boyfriend of Lea Michele. According to the tabloids, he dumped her. So that’s how I know him.

Apparently Matt first came here with Lea as a guest, and after they broke up he decided he’d like a job. To my knowledge, Lea has not been back.

After our motivating treadmill evaluation, we all load into Mercedes Benz sprinter vans for a “warm-up” hike: two hours through the Santa Monica Mountains in the full afternoon sun.

Though they have never met before, the publicist and the mom from Houston quickly establish themselves as leaders of our pack. They have each been to the Ranch multiple times, which makes me question the promise of “sustainable results.” Nevertheless, these women tell me how great the program is any chance they get. They are protective of it, ambassadors almost, even though the Ranch is not paying them; they are paying the Ranch $4,100, each time. “I’m really thankful my husband allows me to come here now and again for my tune-ups,” Ms. Houston says.

When we pull up to the base of the trail, a trainer named Angela leads us in a group huddle, where she tells us to challenge our limits, not limit our challenges. And then she hands us something horrible: plastic bags.

It’s in case we have to poop on the trail.

Everyone nods like this is normal. Is this normal? Prior to this moment, I have gone on exactly one hike (the weekend before, for “practice”). I look around the group and involuntarily imagine everyone squatting and putting their own poop into a bag. Then I imagine Mandy Moore doing it. Oh my God.

Somewhere in the midst of this private horror film, I miss the part where everyone gets their water pouches and backpacks on straight. A trainer named Glenn helps me with mine (I had the hose upside down). And then I set off on the flag-marked trail, five minutes behind everyone else, already sweating from the heat and the fear that I may have to poop sometime in the next four days.

Eventually, I catch up to the stragglers of the pack: the mom and dad from San Francisco. The mom is very nervous about our surroundings, specifically the small plants of unknown origin creeping onto the dusty trail. The publicist and the Houston mom, meanwhile, are so far ahead of us that I can’t see them.

When we reach the end of the trail, the trainers offer us cool, lavender-scented towels from the Mercedes vans, and the publicist breaks the ice with a confession.

“Man, I would love a glass of rosé,” she says, laughing but not joking.

The San Franciscans murmur in agreement, and they admit that they went out to dinner and drinks the night before. Several others reveal they did not give up anything before coming here, blatantly ignoring the rules set out for us in the pre-trip email that I studied for days, worried that we would all be piss-tested for Splenda upon arrival.

There is a lot of lusty talk about wine and sangria and spicy margaritas. It occurs to me that some people might be here to dry out.

Later in the trip, one of the trainers tells me that there was some drama at the Ranch a couple of months ago when the girlfriend of a famous singer came here essentially against her will (the famous singer told her she was fat). During one of the hikes, she sat down in the middle of the trail and refused to go any further. She was screaming and crying, and then the trainer sat down next to her and realized she was high. Later, the program directors discovered she had a cache of pot brownies in her room. (Edible marijuana products were not on the DO NOT PACK list, specifically.)

We carry walkie-talkies on the hikes in case we get lost, and we charge them in our rooms overnight so that the trainers can use them to wake us up. Each morning, I peek out from my plush, white bedding to a crackly summer-camp salute: “Good morning, Ranchers!”

Breakfast is served in the airy greenhouse on the Four Seasons grounds, which is decorated with white linen couches and antique end tables sourced directly from Pinterest. The meal is always 300 calories or less — some combination of fruit, a smoothie, and a special kind of cinnamon oatmeal that the actor describes, very quietly to himself on the first morning, as “cat food.”

In the Mercedes van on the way to and from the hikes, guests discuss friendly topics, including: the benefits of traveling on a first-class-only plane, the scalability of the Dollar Shave Club, and the socioeconomic landscape of Dubai.

Part of the allure of the program seems to be meeting other elites. No one mentions wanting to meet celebrities, of course — that would be gauche. But everyone enjoys making connections with one another, comparing business pursuits, and discussing other wellness indulgences without judgment. (One guest admits to having a masseuse come to their house each day.)

Matthew Paetz typically controls the music in the van. One morning, he plays “Free Fallin’” by Tom Petty. Ten minutes later, he plays “Free Fallin’,” the John Mayer cover.

On the trails, we all keep talking.

Photos: Far Left: Allie Jones; Center Left, Center Right, Far Right: courtesy of The Ranch at Live Oak Malibu for PR

Chatting while hiking is similar to chatting while driving: You can’t really look at the other person, because you have to look out for rocks and poison ivy, so conversation feels freer. I chat with the bride-to-be about bachelorette parties. I chat with her mom about her asthma. I chat with the other mom about the university where one of her sons is going to grad school. I chat with the actor about the Hulk Hogan versus Gawker lawsuit, because he asks me about it and there is no escape.

There is an intimacy to these chats, partly due to the fact that we are all in the same luxuriously deprived boat together. People talk about themselves, and I begin to get a glimpse of some of the real reasons people have come here. I learn that the serial entrepreneur recently broke up with his girlfriend and is trying to keep busy. The actor mentions more than once that he has been having trouble sleeping. The tech worker from Boston really does seem to want to lose weight.

At some point in each hike, people stop chatting and start complaining. This is typically when the trainers offer us a snack. On Day 2 we get six almonds. Day 3 is an apple. Day 4 is four carrot sticks.

The scenery is devastatingly gorgeous, and each day I think I have seen enough after about an hour.

At various points in the weekend, the trainers calmly explain that it possible to lose weight so quickly here because all the hiking increases our metabolism. (The famous publicist tells me one night before dinner that she once came to the Ranch twice within six weeks, and that really got her metabolism going.) The vegan, gluten-free diet, the trainers say, is not so much a crash diet as it is a way to cleanse our bodies from irritants like coffee and bread.

Our meals are mostly vegetables presented in a more interesting way: eggplant with miso sauce, cauliflower made to look like tabouleh, vegan pesto and tomatoes arranged in the shape of a pizza. All the guests proclaim the food to be the best part of the Ranch, and the chef is very nice and very thin.

Perhaps the food tastes so good because there is no choice but to eat it. Before we arrive, the Ranch took care to disconnect room service from our rooms and lock our mini-bars. In my room, however, they forgot to remove a sign saying “Okay, but don’t spoil your appetite,” which taunts me throughout the trip.

On the second night I eat my emergency granola bar.

Throughout the days I feel nauseous, dehydrated, achy, itchy, verklempt, like I have shin splints, like I have a sprained ankle, like my butt is going to fall off. Relief comes each day at 5 p.m., when we return to our rooms after hiking, weight training, and yoga for private, one-hour massages. Afterward, we are invited to take Epsom-salt baths in our deep soaking tubs before wandering over to the greenhouse for dinner. This is virtuous relaxation. Each day, I feel like I somehow earned a massage and a soak in a tub bigger than my bathroom at home.

Everyone who works at the program is a calming presence. The trainers never raise their voices; they carry extra water on the hiking trails for the idiots who don’t bring enough; they walk with the stragglers to make sure they do not get lost. In the mornings before the hikes, they offer to tend to guests’ blistered, swollen feet. Each day, we gather on linen couches in the greenhouse, and the trainers kneel on the ground, taping up and sometimes even lancing blisters. The campers do not seem embarrassed by this, and I can’t help but wonder if this is the first time since they were children that someone has tended to them in this maternal way.

On the final morning of camp, we take a comparatively short hike before our last weigh-in. The air is cool and misty for once, and the actor, perhaps imagining himself in an episode of The Killing, says it feels like we are out searching for a body.

By this time, I have seen all 11 guests in various states of stress and undress, and the only difference I can see after four days is the level of exhaustion in their eyes. The serial entrepreneur reveals he lost eight pounds; the bride lost nothing. I lost five pounds, three of which I gained back within days. And what did we gain?

We survived. We can all go home to our friends and talk about this crazy thing we did. There was an actor there, oh, yes, not Connie Britton or anything, but she goes there, mmhmm. In some cases, we made connections — the publicist invited the San Franciscan couple to an upcoming party hosted by her firm. In some cases, we went two weeks (or four days) without drinking wine or eating gluten. In most cases, we spent a lot of money on something, and maybe that feels like a treat.

Opening Photo: Courtesy of Peter Iovino/©Universal Pictures/Courtesy Everett Collection