In corporate cafeterias, the days of macaroni salad and that orange-marshmallow concoction called Ambrosia are so over. Now you're more likely to find penne pesto salad with roasted tomatoes and yogurt fruit parfait.

The better-for-you food trend has not only prompted a recent flood of new products on grocery shelves and restaurant menus, but it's also pushing institutional food service companies to do some serious menu revisions.

In the past year, major food service companies such as Sodexho USA and Aramark have been rapidly rolling out new food programs in corporate cafeterias, universities, hospitals and other settings in response to improving eating habits and stiffer demands from the corporate bosses who hire them. The changes require big investments, new training, a new culture -- and a lot of faith that the trend will stick.

"It's probably the most significant menu overhaul we've ever taken on as a company," said Chris Malone, vice president of marketing for Aramark, which has spent $2 million in the past year researching and developing its more healthful food initiatives. The old way was turkey with pan gravy, mashed potatoes and broccoli with 372 calories and 17 grams of fat. The new way is honey orange turkey with a baked potato and steamed vegetables with 290 calories and 6 grams of fat.

By the year's end, the Philadelphia company, which had $6.5 billion in U.S. sales last year, will have introduced 1,000 better-for-you menu items into a system that includes 1,300 business dining rooms, 400 college campuses and 400 school districts.

"It's not an optional situation; it's absolutely mandatory to have a healthy option in your cafe today," said Lisa Larsen Hill, senior vice president for corporate services for Gaithersburg's Sodexho, another institutional food giant with $5.8 billion in U.S. sales last year. This year, the company unveiled a menu program called "Your Health, Your Way," available at its more than 1,300 corporate locations.

In Sodexho's cafeterias, Hill said, fried chicken might be on the menu once a year. Instead, diners are more likely to feast on balsamic chicken and polenta with steamed broccoli and red peppers, which has 350 calories and 6 grams of fat.

The demand for more nutritious fare has come in waves. College students were already pushing cafeteria operators to offer more freshly prepared foods -- such as omelet and pasta bars -- as well as more vegetarian options. At the primary education level, school boards concerned with obesity among schoolchildren have pushed for more healthful food. Hospitals, too, have been putting pressure on food service companies to provide more choices in their cafeterias and more room-service style service to patients.

The changes in business cafeterias and dining rooms have been more dramatic. Aramark first introduced lower-calorie menu choices in 2001, Malone said, but they didn't sell. "Our interpretation at that time was that while people were talking differently, they weren't eating differently," he said.

But these days, food service companies can't roll out more nutritious dishes soon enough for impatient corporate employers. The movement crystallized early last year, industry executives say, when the low-carb craze began to take hold, the media began following the obesity issue, and corporate employers responded by making nutritional demands. They saw their workers' newfound interest in lower-fat, lower-calorie and lower-carb meals as another way to tackle rising medical costs and lost productivity.

"As a company, we want to give our employees the information and the tools that are necessary to eat healthier and live better lives," said Diane Santen, manager of facilities at defense contractor Northrop Grumman's McLean campus. Since Sodexho installed its new program at the complex, Santen said she has "really observed employees eating healthier."

The National Business Group on Health, a Washington nonprofit that works on health issues in the workplace, is developing standard contract language that employers can use in negotiations with their food service vendors, outlining the need for healthful options, nutrition information and education. "We're really expecting a sea change in the way employers deal with their food service vendors," said Helen Darling, the group's president.

Though there are numerous regional food service companies, most of the corporate cafeterias in the country are run by one of three main players: Aramark; Sodexho USA, a division of the French company Sodexho SA; or British food service giant Compass Group, which rang up $5.7 billion in sales in its North American division.

The push to change is having a big impact on the culture of the food service industry, as dining room workers dispense nutrition information and on-site chefs find they have less creativity. When the marketing materials for a new dish say it has 360 calories and 6 grams of carbs, the dining room's executive chef can't be topping it with a cream sauce because it might taste better.

And taste is a big part of the reason that institutional food service providers have relied for so long and so heavily on sauces, deep frying and added fat -- people like it. That has been a mandate for cafeteria operators, said Joe Pawlak, senior principal with the restaurant and food service consulting firm Technomic in Chicago, because employers want to encourage the use of company dining rooms so workers will take shorter breaks and be more productive.

"To do that, [food service operators] have to provide good-tasting food, and sometimes good-tasting food doesn't always mean it's healthy," he said. "They have to be more skilled, and they are becoming more skilled, at menu development."

Aramark did market research to understand types of diners and what they eat. It came up with six dining profiles and conducts surveys at each cafeteria to tailor its menu mix.

"We have to match the needs of very different populations -- from investment banking to credit card processing plants," said marketing director Malone. When a client has a large proportion of healthy eaters, Aramark might offer more menu choices such as broiled salmon and steamed broccoli, while at workplaces where the diners are less diet-conscious, pot roast and pizza are on the menu more often.

Sodhexo reduced the number of menu choices available at each location from 8,000 to 1,300, most of which are new creations. Some of the discarded recipes "were old and out of fashion," Hill said -- like the macaroni salad.

Yet food service providers know they must offer more choices because the healthful options must exist alongside the favorites that many customers still want, such as french fries and cheeseburgers. That has made business more complex.

"You run out of space, and it gets more expensive because you're offering so may different choices," said Deanne Brandstetter, director of nutrition for Compass USA. Brandstetter said about half of its menu choices are considered healthful options, such as broiled fish instead of fried, compared with about 20 percent three years ago.

In some cases, Brandstetter said, the extra cost of these expanded menus are being shouldered by Compass, but some employers have agreed to pay more to get more healthful food for workers. In other cases, she said, prices are going up.

The big three in the business all say the change is worth it because sales of the new menu items have been so strong.

"It's enlightened self-interest," Malone said. "This is a big business opportunity for us."

Food service giant Sodexho's menu items in Northrop Grumman's McLean campus are more healthful than they used to be. A facilities manager at the campus said she has observed more nutritious eating habits since the switch.