He joined the company in 2013 after being approached by CEO Tom Linebarger with a puzzle and the desire to try something new. For years Cummins had preached the gospel of “wellness” to its 55,000 employees. Workers were encouraged to complete health risk assessments and undergo biometric screenings; they could rack up points and earn discounts on their insurance premiums by logging physical activity and attending health-related lunches. There was just one problem. It didn’t seem to make a difference.

Year after year, Cummins’s health care costs continued to rise. So did the prevalence of disease at the company. Its largely Midwestern workforce suffered from problems typical of an aging population—obesity and related chronic conditions—and its long-running efforts to promote wellness hadn’t changed that. “We’re paying a lot for this stuff,” Shurney says, but he couldn’t help wondering, “What are we getting?”

Linebarger challenged the team to approach the organization’s health with the same rigor and Six Sigma precision that Cummins applied to its engines—pushing them to get to the root causes of the company’s exploding health care costs.

Shurney knew health was “produced” between doctor’s visits, but how best to nurture it among Cummins’s global employees was something he spent the next year, steeped in research and consultation with experts, trying to figure out. The result is hard to describe—and it’s a work in progress, he stresses—but it seems that he’s edging closer to what has become something of a holy grail in his line of work: a wellness program that actually moves the needle.

Employee wellness programs have long been billed as something of a magic bullet—a low-cost means to a happier, healthier, more present, more productive workforce: a win-win-win-win. (There are also studies out there—albeit controversial ones—that suggest that the workplaces with the best wellness programs significantly outperform the stock market.)

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It’s a tantalizing promise, and over the past decade businesses large and small have rushed to cash in. Part of the push, of course, has come from a big, swinging stick: soaring employer health care costs. But part has come from a carrot too: The Affordable Care Act allows employers to tie up to 30% of a worker’s insurance premium (or 50% in the case of smokers) to health outcomes such as weight loss and smoking cessation achieved in wellness programs. (In other words, employees who don’t meet health goals pay more.)

The result is that workplace wellness programs are now practically universal in corporate America—a fixture of modern work culture as familiar as the on-site cafeteria or the 401(k) plan. And the wellness industry behind them has created an $8 billion industry.

While enthusiastic in their uptake of such programs, however, corporations have generally been content to outsource them—and then pay little attention—to an assortment of vendors and consultants. And that’s where the promise of a head-turning return on investment meets a less handsome reality.

Indeed, in some cases, such wellness initiatives seem to be piling on both employer and employee expenditures. As health care costs have continued to climb, many companies have simply doubled down, signing up for increasingly sophisticated and robust wellness add-ons. Incentives for employees to participate now average $651 per year, according to one industry estimate, as workers are offered a bevy of new self-improvement services.

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Wellness programs, in fact, have morphed into hydra-headed beasts of “well-being”—with corporations relying on vendors not just to promote exercise, but also to help employees attain mental, emotional, spiritual, and even financial health. (In Fidelity’s 2016 Employer-Sponsored Health and Wellbeing Survey, 76% of 128 large employers reported having a “financial security” component.)

Employee attitudes toward this workplace movement are often more complicated than those of employers. Some are wary of sharing health data; others are busy or overworked and resent the added burden—it’s just another thing they have to do. For these reasons and others, employee participation in corporate wellness programs—even when they’re paid for it—is pretty low. Engagement ranged, for example, from 10% (life coaches) to 53% (completing a basic health questionnaire) in the Fidelity survey.

Meanwhile, whether wellness programs actually work—either by significantly improving health outcomes or by reducing health care costs—has become a subject of surprisingly fierce and unresolved debate. Though the industry has churned out plenty of data in its support, the most credible research—including a federally commissioned Rand report from 2013—suggests mixed, if not ambiguous, results.

While one can certainly point to success stories—Johnson & Johnson touts big savings from its 38-year investment in employee wellness—low participation, along with the diversity of programs and the generally squishy science of “wellness,” has made calculating the industry’s average ROI and general effectiveness challenging and contentious.

Ron Goetzel, a senior scientist at Johns Hopkins Bloomberg School of Public Health and a vice president at IBM Watson Health, believes well-designed, properly implemented, and rigorously evaluated wellness programs can make a difference. (Culture and strategic communications are key.)

But Al Lewis, the industry’s most vocal critic—he’s also an industry defector who now runs an “employee health literacy” company called Quizzify—says they’re an utter waste of money. And worse: potentially harmful. He’s not bothered by “wellness done for employees”—gym reimbursements, healthy snacks around the office—but rather what he calls “wellness done to employees.” He includes in that category weight-loss requirements (or resulting penalties) imposed on workers and annual biometric screenings that flout standard guidelines.

On the plus side, such assessments allow employees to become acquainted with their own health risks (high cholesterol, elevated blood sugar), and they establish a baseline that makes it possible for them to track their progress toward meeting health goals over time.

But Lewis and others contend that these frequent screenings are superfluous and expensive and can lead to false positives and overtreatment. The state of Nebraska was criticized, for instance, for encouraging all its employees to undergo a colonoscopy. (The U.S. Preventive Services Task Force, as a rule, recommends the screening procedure only for those over age 50.)

It was this sort of overreach that inspired Shurney and Cummins executives to think twice about their approach to health and wellness.

And after a yearlong research effort, the company is slowly rolling out a new program to Cummins employees and their families. The aim is to change lifestyles through better management of seven factors—physical activity, sleep, nutrition, stress reduction, substance abuse, water, and sunshine—and Shurney has put together what he calls “a continuum” of services to address this goal.

In his research, Shurney discovered that employees know far less about these things than they think they do—for instance, few understand the relationship between sleep and obesity or realize that chicken has far more cholesterol than peanut butter—and he worked with the American College of Preventive Medicine to develop a curriculum for them. That education happens in the company’s clinics, but it has proved especially potent in Cummins’s Comprehensive Health Improvement Plans—intensive, seven-week lifestyle-training programs in which employees have seen dramatic reductions in weight and cholesterol levels.

Shurney says Cummins is on track to reverse Type 2 diabetes in 10% of identified employee patients this year. And given that drugs are the fastest-rising cost in the system, that wellness investment may just pay off for the company after all.

A version of this article appears in the March 15, 2017 issue of Fortune as part of our 100 Best Companies to Work For package.