early five years ago, the global health organization AmeriCares started a mobile clinic in the chaotic slums of Mumbai, where sanitary facilities and running water are limited and entire families sleep in a single room. Throngs of residents who simply can’t afford bus fare to a local hospital line up outside roving vans to receive treatments for a host of respiratory and gastrointestinal disorders. Around the same time, the so-called Health Wagon began traversing rural Appalachia, offering screening for diabetes-related eye disease to malnourished mountain dwellers.

Since these innovative programs took root, mobile clinics have blossomed around the world to provide health care to those who are unable to procure such services themselves. According to the American Journal of Managed Care, there are now nearly 2,000 such programs in the U.S. alone. Most of the millions of patients are homeless, disenfranchised, displaced, or uninsured. Most. But not all.

On a late-summer afternoon in Northern California, another mobile clinic is stationed in a more improbable location: among the BMWs bmwyy and Teslas TSLA in the parking lot of the highly groomed corporate headquarters of Nvidia NVDA , a graphics semiconductor titan in Santa Clara County, home to the nation’s highest median household income. The estimated average annual salary on this campus: roughly $130,000. And yet there’s a sparkling 37-foot RV with two exam rooms and a lab. It bears the markings of the Palo Alto Medical Foundation (PAMF), a nonprofit with 15 offices in the Bay Area.

The Care-A-Van, as it’s called, serves more than a dozen of Silicon Valley’s largest employers, including eBay EBAY , Juniper JNPR , Oracle ORCL , PayPal PYPL , SanDisk SNDK , and VMware VMW , as well as Nvidia. Inside, the on-duty physician, Haleh Sheikholeslami, explains that she has had some dramatic encounters during two or so years on wheels. She has diagnosed a few heart attacks and recently dispatched an engineer complaining of chest pains to a hospital, where he immediately received four arterial stents. Mainly, though, the diagnoses are more routine, at least until you consider that the average age of her patients is under 40. She sees mental-health issues associated with chronic stress and anxiety, from rashes and irritable bowel syndrome to full-on depression. Many patients are deficient in vitamin D—in a climate that sees 260 days of sunshine per year—and have eye, back, and other muscular complaints related to repetitive motions and a lack of physical activity.

Milpitas, California - October 1: Sutter Health's "Care-A-Van" travels to a variety of sillicon valley companies, providing on site exams. The medical van open for patients outside the offices of SanDisk in Milpitas, Calif.Photograph by Brian L. Frank for Fortune

Most of all she sees cholesterol problems, high blood pressure, and elevated triglycerides, all stark signs of an increased risk of diabetes and heart conditions. “They get what we call metabolic syndrome,” says Sheikholeslami. “They’re overweight. The good cholesterol is low, their triglycerides are high, and that leads to a variety of issues.” Unlike most mobile-clinic visitors, nearly every Care-A-Van patient has health insurance. A full 40%, however, don’t have a primary-care physician. For some, that’s because they’re immigrants who haven’t bothered to navigate the U.S. health care system. Others just can’t break away from the workload. Some patients don’t even get off their mobile devices while being examined.

Ronesh Sinha, an internal-medicine physician and PAMF’s director of employer health services, enters the RV and picks up the thread. “You’d think when you go to companies that offer great health insurance, on-site gyms, and extensive wellness programs that you wouldn’t be seeing the issues we’re seeing,” he says. “But people are so freaking busy they can’t even imagine going out to the doctor.”

Sinha, who specializes in health and wellness issues with a special interest in Asian, and in particular Indian, patients, started the Care-A-Van in 2013 after he noticed some alarming trends. First, he was seeing far fewer patients than what he considered normal. Next, the patients he was seeing had bodies that didn’t match their age. A toxic cocktail of poor nutrition, sleep deprivation, and stress, he surmised, is causing an epidemic of advanced aging in Silicon Valley. He tells of a 34-year-old programmer who came in complaining of neck pain. X-rays revealed severe degenerative arthritis caused by poor posture, insulin resistance, tissue inflammation (a result of the insulin resistance and a diet high in processed carbohydrates and sugars). It was the type of affliction a doctor would typically find in someone around 70. Sinha says he commonly sees 30-year-old engineers with 50-year-old bodies, complete with potbellies, curved spines, dulled skin tones, joint issues, reduced vitality, and elevated risks of diabetes and heart disease.

Milpitas, California - October 1: Dr. Ronesh Sinha, photographed outside Sutter Health's "Care-A-Van" which travels to a variety of sillicon valley companies, providing on site exams. Dr. Ronesh Sinha in front of his Care-A-Van, which he launched in 2013.Photograph by Brian L. Frank for Fortune

He was also noticing that Asian patients were faring worst of all. As an Indian-American, Sinha is acutely aware of the prominence of Asian workers in the Valley. He used to struggle with his weight and health, so he knows firsthand that the Western metrics don’t always apply. Many studies have demonstrated that Indians, despite being nominally less obese than other ethnicities, have a higher risk of diabetes and heart disease. Part of the problem is that they tend to carry weight differently than Westerners; they have thinner arms and decreased musculature. As a result, their body mass index, or BMI, tends to be lower, causing them to fall under the radar. But Indians have a higher propensity for belly fat, which is the most dangerous kind. For all these reasons Sinha decided to borrow an innovation from the most marginalized populations of humanity and roll it out on the gilded streets of Silicon Valley.

Sinha—or Dr. Ron, as he's known—

is a whirlwind. Aside from his work with PAMF, he maintains a private practice. His exercise routine, including high-intensity sprinting, and a nutrient-dense, low-carbohydrate diet account for his trim figure. He wrote the South Asian Health Solution, a book that offers accessible explanations of nutritional science along with diagrams for how to achieve the perfect forearm-side-plank yoga pose. He’s got a blog and three ebooks, he’s given two TEDx talks, and he’s a regular on the Valley lecture circuit, where he hosts standing-room-only discussions on such topics as “How to Prevent a High-Tech Heart Attack.”

Sinha is quick with anecdotes to demonstrate the outsize incidence rates in tech companies of everything from high-risk pregnancies to auto-immune disorders. But at a certain point, anecdotes aren’t enough. Everyone in the Bay Area seems to know someone who works 18-hour days, looks like a zombie, and relies on Red Bull, Adderall, or even cocaine during the sprints to make a deadline. But hearsay doesn’t make an epidemic. So I ask Sinha for hard data, and he invites me down for another visit.

We meet on the back patio at a Cupertino Starbucks SBUX . After some small talk, he hands me a seven-page document detailing the results of a biometric screening performed at one of PAMF’s clients. We agree to keep the company anonymous. Suffice it to say it’s a large Silicon Valley employer. Sinha assures me that the demographic makeup of the participants is typical of the rest of his clients. And so are the results.

The screening tested nearly 500 employees, primarily in search of insulin resistance, a condition that prevents the body from properly processing the hormone that promotes the absorption of glucose from the blood into your cells. In insulin-resistant bodies, the insulin and glucose are repelled by cells. Rather than being used by muscles for energy, the glucose is redirected to fat cells. There is no universally accepted cause, but there is plenty of published evidence that obesity plays a role. Overweight people become more resistant, which causes them to become fatter in a vicious cycle. Sinha and others make a convincing case that the primary culprit is a diet high in processed carbohydrates and sugar. Many studies have also demonstrated that insulin resistance is triggered by stress, sleep deprivation, and a dearth of physical activity.


Viewed in that light, the typical tech company looks like a perfect breeding ground for insulin resistance. Employers often provide copious amounts of processed, sugary, high-carb snacks, energy drinks, and soda as a perk to workers, often for free. Employees sit at their desks all day and into the night. And of course, everyone is crazed about a deadline and competing like hell to keep up or get ahead. The effect is unsurprising. Remember the “freshman 15” from college? In the Bay Area, people talk about the “Facebook 15” and even the “Twitter 20” TWTR .

Most commonly, doctors look for increased levels of LDL, the so-called bad cholesterol, when examining for risk of heart disease. Sinha emphasizes another measurement. “The LDL measured on a standard cholesterol test is not what’s causing most of the heart disease,” he says. “Heart disease is far more complex, and the root cause is inflammation.” So PAMF focuses on the ratio of triglycerides to HDL—the “good” cholesterol—while plotting ethnically adjusted BMI and waist-size statistics. This shift in lenses has a remarkable effect on outcomes.

When only LDL is looked at, roughly 25% of Caucasian participants in Sinha’s screening demonstrated borderline-high or high levels of cholesterol. For Asians and Indians, the number is 19%. But viewed through the triglyceride-to-HDL lens, 30% of Caucasians are in the danger zone. For Asians, it’s 40%. Indians have the worst percentage of all: 55%.

When all the factors—blood pressure, cholesterol and triglyceride levels, waist circumference, and BMI—are considered in combination, the numbers are even grimmer. Nearly 75% of Caucasians in the survey have at least one risk factor for diabetes or heart disease. Among Asians, it’s 81.8%. For Indians, 92%. This is no small affair considering that more than half of the Valley’s tech workers are Asian.

Milpitas, California - October 1:Gena Rayford draws and examines blood samples from Teja Krishna Bagenalli, a patient aboard Sutter Health's "Care-A-Van" which travels to a variety of sillicon valley companies, providing on site exams. Preparing to draw a patient’s blood in the mobile medical van.Photograph by Brian L. Frank for Fortune

Those numbers aren’t quite as stratospheric as they might seem to a layperson—but they’re still telling. Or so I discover when I share Sinha’s numbers with four epidemiologists and public health experts. Americans overall have high risks for diabetes and heart disease. But there’s a crucial caveat. “In the general population in the U.S., diabetes and cardiovascular disease are associated with low education and incomes,” says Adam Drewnoski, a professor of epidemiology and director of the Center for Public Health Nutrition at the University of Washington. Sinha’s findings, as we’ve seen, are drawn from some of the most educated and affluent people in the country.

I get a similar response from Robert Lustig, a professor at the University of California at San Francisco, an expert in pediatric obesity and diabetes, and the author of Fat Chance: Beating the Odds Against Sugar, Processed Food, Obesity, and Disease. Referring to a recent diabetes study that focused on Indians (and used different methodology), he says, “The percentages in the Silicon Valley sample seem much higher. You would think an educated population would do better. But not necessarily. The people in Silicon Valley are eating a terrible diet of processed and sugary foods, and Asians and Indians can least afford to do this.”

Sinha’s conduit to his clients is human resources. But none of his HR contacts would talk for this story. Instead, I speak with Lisa Yee, executive director of the Silicon Valley Employers Forum, which represents HR-benefits directors at 40-odd Bay Area companies, from Adobe ADBE to Yahoo YHOO . Yee says many wellness programs aren’t working. “I’ve talked to every one of the high-tech firms, and this is their No. 1 priority,” she says. “ ‘We offer a plethora of programs, but they’re not getting the traction we’d hope given the investment we’re making.’ That’s what I keep hearing.”

“People are asking me for a combination prescription: Ritalin and Xanax. One so they can perform during the day and the other to knock them out at night.”

Yee says there’s a lot of blame to go around. For all the talk in the Valley about the power of big data and analytics, some of her members are guilty of not adequately measuring the efficacy of wellness programs, which seek to encourage healthy habits among employees (more on that later). And then there’s the Valley’s productivity-first culture. “I really believe a case in point is Yahoo,” Yee says. “So Marissa Mayer is going to have twins. That’s great. She can have a career and have a family, and she can obviously afford all the care at home to take care of those kids. But working right up until the end of her term, what message is she sending? Is it that productivity is what really matters? That’s counter to what HR is trying to provide, a work-life integration and balance.”

A lack of that balance can have many ramifications. So says my Bay Area doctor, Bertrand Vandeville. After a recent exam I asked what kinds of issues he’s been seeing lately. “People are coming in asking me to fill a combination prescription: Ritalin and Xanax. One so they can perform during the day and the other to knock them out at night,” he says, making me feel less guilty about my own coffee and wine routine. “And there are a lot of young people in their twenties and thirties who get these prolonged respiratory issues in the winter. You’re not supposed to be sick for weeks at a time, but that seems to be becoming more normal. It’s all stress related.”

Stress triggers the body to release cortisol, a hormone that can make you feel hungry and crave junk food, which boosts insulin resistance and abdominal fat. Heart disease may be the most dramatic manifestation. “But for other folks it’s just depression,” Sinha says. “I see people who have no reason to be depressed. No family history of depression. Their marriage is fine; their finances are in order. But the stress overcomes them. For other folks, it’s chronic pain or gut-health issues. All these things are clearly lifestyle induced.”

Sinha's data got me wondering whether the Centers for Disease Control and Prevention is clued in to this phenomenon in the Valley. When I ask a CDC official to dissect the PAMF screening, I’m told it’s against agency policy to comment on private data. Indeed, comparing Sinha’s findings to CDC reports seems nearly impossible, and his data team argued against it. For starters Sinha uses ethnically adjusted metrics; the CDC doesn’t. His tests employ a higher threshold for hypertension and don’t require participants to fast for 12 hours before taking a glucose test (which is seen as important when testing one individual but is impractical in doing a companywide screen). Despite those significant caveats, a rough comparison gives at least a sense of scale. According to the CDC, in 2012, 35% of all U.S. adults and 18% of those under 40 had at least three metabolic risk factors. In Sinha’s screening, the number for Caucasians is 29%, which is significant considering how many Valley workers are under 40. For non-Indian Asians, the number is 46.1%, and for Indians, it’s a whopping 54.2%.

The Valley is an interesting place to observe the spread of such conditions. If the affluent, educated people here are succumbing, it says a lot about the dramatic and deleterious health effects of a desk-centric, high-stress lifestyle. Another reason the Valley makes an interesting petri dish is the tendency here to turn problems into opportunities. Countless brilliant students, entrepreneurs, scientists, and capitalists flock here to optimize systems and profit from the improvements. So perhaps as these issues emerge, so, too, will solutions that guide the rest of the culture.

Most Silicon Valley companies already have some type of wellness program. They vary greatly in execution and effectiveness. Some feel half-hearted: perhaps a 10-class yoga series in a conference room and stress and diet advice on the company website, along with a regular “healthy” option in the cafeteria and maybe a gym. Dr. Jordan Shlain, who sees patients in San Francisco and the Valley, dismisses such efforts. “There’s zero evidence to show that corporate wellness programs do anything for health at all,” he says.

A few Bay Area companies, including Applied Materials AMAT and Facebook FB , are more engaged, making health and wellness options as accessible as snacks typically are. They’ve deployed elaborate on-site health centers with the help of Crossover Health. Facebook’s wellness center offers primary, urgent, and online care, as well as physical therapy, chiropractor and acupuncture services, and various health-education and behavioral health services. Having a world-class facility right on campus seems to boost engagement dramatically. “Of the eligible Facebook employees, 65% have used the health center,” Crossover CEO Scott Shreeve says. “The center is typically oversubscribed.”

Apple has a center too—also managed by Crossover—which comes off as more of an Apple Store than a doctor’s office. During an interview last year with Fortune, Apple’s head of HR, Denise Young Smith, said that 43,000 employees had visited one of seven on-site doctors during the first year and that the center has an average wait time of less than five minutes, as well as a team of chiropractors, physical therapists, and dietitians. Shreeve says that workers who use the centers his firm manages make noticeably fewer visits to emergency rooms and are dramatically less likely to be hospitalized than their peers at the same companies.

There are also a raft of companies trying to solve health issues through digital means. Chief among them, perhaps, is Omada Health, which in September added a $48 million third round of financing to fight obesity-related chronic disease, which is estimated to cost the economy $500 billion a year. Omada is working with employers and insurers to offer its diabetes-prevention program as a standard of care. Omada mails each member a digital scale with a cellphone chip to log weigh-ins automatically, and pairs each individual with a health coach for a 16-week curriculum to create a more sustainable lifestyle. “The goal is to help you lose the right amount of weight in the right sort of way that science shows can have an impact on your health and diabetes risk,” says Omada co-founder and CEO Sean Duffy.

Duffy says there’s a rising tide of obesity-related consequences in California. He points me to the annual “State of Obesity” report prepared by the Trust for America’s Health and the Robert Wood Johnson Foundation. In 1990, less than 10% of Californians were obese. Last year the figure was almost 25%. The amount of obesity-related cancer here is projected to more than double in the next 15 years, according to the report, and heart disease is expected to quadruple. “Even a couple years ago there was a general attitude that this was other people’s problem. But it’s here now. It’s in the home base,” says Duffy. “It behooves Silicon Valley companies to look at themselves in the mirror.”

I'm sitting across the table

from, oh, let’s call it roughly $10 billion in net worth. Most of it belongs to Dustin Moskovitz, one of the co-founders of Facebook and the former Harvard roommate of Mark Zuckerberg. Justin Rosenstein hasn’t done too badly either. He started his career as a product manager at Google GOOG , where he invented Google Drive and Google Chat. He was then lured to Facebook by Moskovitz to lead the technical team that invented the ubiquitous “like” button, among other projects.

Moskovitz and Rosenstein made their fortunes on the backs of breakneck work cultures, and now they’re feeling some regret. Here’s Moskovitz, recounting Facebook’s early days. “Work was at the center of our lives. We weren’t necessarily trying to deliberately craft one of these Amazon-like cultures that are so extreme, but it was sort of the way of the Valley,” he says. “We just got sucked in, and it had a bunch of negative health consequences on me as a result.” Physical? Mental? “Yes. Yes. Both. Back problems and just general unhealthiness. I gained a bunch of weight, wasn’t fit, and I’d get winded if I went up the stairs too quickly,” he continues. “The Facebook meal plan was reasonable, but we had a lot of unhealthy foods stocked. So I would eat some form of candy probably every day. Lots of soda. Probably more soda than water.” For his part, Rosenstein had worked 65-hour weeks at Google. “It was starting to take a toll,” he says. “I was pretty miserable for a lot of that time.”

Moskovitz and Rosenstein left Facebook in 2008 to start Asana, which makes software to facilitate teamwork and boost productivity while minimizing email. We’re sitting in the company’s headquarters in San Francisco’s Mission District, discussing the philosophy of Asana’s culture, which they conceived around the time they were trying to recruit old friends and colleagues. “Coming out of Facebook, a ton of people got burned out. To me, that’s kind of a tragedy, because we invested in these people and made them better,” says Moskovitz. “And now they’re just not contributing to the economy.” Adds Rosenstein: “It’s amazing how many people were just like, ‘I can’t work any more.’ ”

“Coming out of Facebook,” Moskovitz says, “a lot of people got burned out. Now they’re just not contributing to the economy.”

The duo decided to tackle the problem by crafting a more mindful and, they hope, sustainable way of working. They call it the Asana Way. Rosenstein shares a three-page outline detailing its tenets. Some are awfully squishy, à la “Hire egoless people” and “Don’t work ridiculous hours (but can when need to).” But others are thought provoking. One especially enlightened policy has to do with responsibility allocation. In a typical culture, a designer, for example, would create an asset and run it by the boss for approval. At Asana, the boss works more as a mentor or an adviser. Which means Rosenstein provides feedback, but the designer can choose whether to take it. “Often they’ll take my advice because they respect me. But if they disagree, they make the call. Of course I can, you know, relieve them of their responsibilities, but short of that they really are the empowered decision-maker,” he says. “There’s tons of times when I don’t get my way. But in the long run that leads to a culture in which people really feel in control of their destiny. So we can hire better people and retain them for longer.” The phenomenon is not exclusive to Asana: Many studies link having a “high control” job—one that offers autonomy—to good health.

The Asana Way emphasizes transparency. Most financial details are shared throughout the company. It also attempts to minimize meetings (never on Wednesdays, for example) but encourages employees to dine together to boost camaraderie. Breakfast, lunch, and dinner are served three days a week in a sleek dining room, and the in-house culinary team emphasizes fish, chicken, and vegetables with no processed carbs or dessert. Physical and mental health are priorities. There’s yoga every day, and top executives routinely attend. Moskovitz says he has pushed employees to take vacation or exercise more. Each employee is provided with a standing desk, an ergonomic consultant, and $10,000 to optimize a workstation.

Above all, the Asana Way is about balance. Rosenstein clearly has a New Age streak and talks a lot about mindfulness. He meditates nearly every day, sometimes in the office. But he says he was also highly influenced by the Power of Full Engagement, a 2005 management book by Jim Loehr and Tony Schwartz about optimizing productivity through awareness and work-life balance.

Not everything has gone perfectly. One early principle was to avoid titles in hopes of breeding a more meritocratic environment. But Moskovitz and Rosenstein have lately realized the folly of empowering a recent graduate with as much authority as someone with a decade’s experience. So they’re rethinking that policy. But overall this holistic approach to building a healthy work culture seems to be paying off.

Moskovitz and Rosenstein have no hard evidence, but anecdotally staffers have told them they are in better shape and less stressed out. Asana recently hired a consulting firm to conduct an employee-satisfaction survey. According to figures Asana showed me, the company scored in the 98th percentile on employee engagement. They cited empowerment, values, and communication as the three biggest drivers. (The company’s actual business is doing well too. Asana claims to be one of the fastest-growing software-as-a-service companies in history, with more than 140,000 customers.)

For Moskovitz and Rosenstein, the personal returns have been positive as well. Rosenstein says he’s down to 50-hour weeks. As for Moskovitz’s back? “It hardly hurts at all,” he says.

I've been reporting

on Silicon Valley for two decades, through good times and bad, and I felt as though I had heard just about everything. And then one day Sinha characterizes the plight of the Valley worker in a way I never would have considered. “The extent of human suffering here,” he says, “is pretty intense.”

It made me wonder. Have I been missing the signs? Are people here secretly unhappy? So I call the employer-review site Glassdoor. It doesn’t measure happiness per se, but it does rank attitudes toward “work-life balance” and “compensation & benefits.” I ask it to assemble a report comparing the rankings at 40-plus Valley firms with those at Manhattan financial firms, Detroit automakers, Philadelphia legal firms, Boston health care companies, etc., and another report comparing Valley tech companies with tech companies in Seattle, Boston, New York City, and elsewhere. The results reaffirmed my instincts. With a few exceptions, the firms in the areas around San Francisco and San Jose show up near or at the top. Even with all that suffering, people in the Valley think life is good. But why?

Maybe it’s because they’re getting exactly what they had signed up for. They’re well paid, intellectually stimulated, and surrounded by people who feel as though they’re working for a cause. If they have a few strong objections about a lack of work-life balance, maybe they never expected such a thing. They arrived fully aware of the intensity and demands, presuming to throw themselves entirely into their work, to sleep under their desks or not at all. Besides, many of their needs are accounted for. Their hair is cut, their dry cleaning delivered, their transportation provided. Then there’s all the food. Silicon Valley has long been a locus of desk work and high stress. But the cornucopia of food is relatively new. Google started offering its famous free spreads in 1999, toward the end of the dotcom boom. In this latest economic explosion, many others have followed suit. Food has become both a recruitment tactic and a way to keep workers on campus and boost productivity. It may also be precisely what has, ahem, tipped the scales to make Silicon Valley’s work culture unsustainable.

In the 2009 book The End of Overeating, former FDA commissioner David Kessler explores the biological effects of energy-dense, “highly palatable” foods. These foods, he writes, stimulate the brain’s opioids, also known as endorphins, a process similar to the one incited by morphine and heroin. “In addition to their stimulating effects,” he writes, “the opioids produced by eating high-sugar, high-fat foods can relieve pain or stress and calm us down.” Kessler, who took on Big Tobacco in his FDA tenure, directs his glare to big food companies. But in this case, assuming the findings of Dr. Ron and his contemporaries are as scary as they seem, the tech companies themselves deserve blame as well. In optimizing a work culture in the name of productivity, they appear to have minimized the importance of humanity.

In my final conversation with Sinha, I ask whether he considers Silicon Valley a dangerous place to work—because the picture he paints is of a ticking time bomb. He pauses for a moment and tells me I need to understand his perspective. Most of the people he’s seeing are the ones who are reaching out for help, the ones who are suffering. And then, “I guess in some ways, it is. But the way that the time bomb is going to explode is different in each person,” he says. “We have the impression that urgent conditions will present themselves in an urgent way. But most people don’t have television-style heart attacks. In a lot of cases it’s low-grade conditions that have been there for a while. The problem is when we’re this busy, we can just put that on the shelf and attend to our meetings, because work is always No. 1.”

Jeffrey O’Brien is a former Fortune senior editor and co-founder of StoryTK, a Bay Area studio that crafts stories for companies.

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A version of this article appears in the November 1, 2015 issue of Fortune.