By Anne Fisher in FORTUNE Magazine

Eight out of ten employees now gulp a quick lunch at their desks, says a new survey. But not taking a breather during the day, even for just a few minutes, is a recipe for burnout.

Lunching al desko again today? You’ve got lots of company. Only 21% of people now regularly leave their workstations for a midday meal, according to a poll of 1,023 U.S. employees by talent development consultants Right Management.

These days, “far fewer employees are feeling comfortable enough with their work loads to take time away” for a quick bite, notes Michael Haid, a senior vice president at the firm.

Haid adds that many companies’ cultures make people feel they need to apologize for stepping away from the grindstone even for 30 minutes. “One has to ask if such pressure, without any let-up, actually benefits the individual or the organization,” Haid says. “I mean, does it really improve performance? We are definitely not talking about a return to the days of the three-martini lunch, but have we gone too far in the other direction?”

He thinks so. Employees fearful of being seen as slackers “begin to sacrifice their own break times in order to keep up with their workloads. So, whether the organization is imposing unrealistic workloads or whether employees are progressively giving up their own break times, leaders need to pay close attention and understand the early warning signs” of burnout, Haid says.

Tony Schwartz, head of New York City-based productivity consulting firm The Energy Project, says more and more companies are starting to recognize the problem. “What’s at risk, when employees are overworked and stressed out, is their capacity to do great work,” he says. The Energy Project’s clients — including Bristol Myers Squibb (BMY), Apple (AAPL), PwC, Google (GOOG), Sony (SNE), Ford (F), and Ernst & Young — “see a clear link between exhausted employees and poor performance. Avoiding burning people out is critical to success, both for companies and for individual bosses.”

A big part of keeping burnout at bay: Encouraging employees to take a break now and then. “When demand in our lives intensifies, we tend to hunker down and push harder,” Schwartz observes. “The trouble is that, without any downtime to refresh and recharge, we’re less efficient, make more mistakes, and get less engaged with what we’re doing.”

The paradox here, he says, is that “by pushing people too hard, you actually make them less productive. But if employees learn to manage their energy better,” partly by taking short respites from work throughout the day, “they get far more done, and add much more value, in far less time.”

Curious about how well (or how badly) you, or your employees, are managing energy? The Energy Project has devised a quick 20-question quiz, administered to thousands of employees over the past decade, to help people pinpoint whether they might be headed for burnout. The results, Schwartz says, are usually “depressing but eye-opening. The average score is 14, meaning that, out of 20 behaviors people regularly engage in, 14 are energy-depleting.”

One of those behaviors is — you guessed it — skipping lunch breaks. “Letting employees recharge at midday is a tremendous competitive advantage,” Schwartz says. “Look at Google. Everyone goes to lunch there. The food is great, and it’s free. And people are having terrific conversations in the dining room.

“Facebook and Twitter now offer the same thing, that chance to connect with colleagues and share ideas over a relaxing meal,” he adds. “Obviously, these are highly successful companies, with forward-thinking management. Look at what’s happening there, and you’re seeing the future.” One can only hope.