Consider it the new math for restaurant operators: addition through the subtraction of additives.

Numerous limited-service restaurant companies are rushing to remove foods with antibiotics and artificial flavors, colors, and preservatives from their menus in an effort to meet the growing demands of consumers. The list of operators working toward creating “clean” menus is growing, including some of the nation’s largest operators. Chains as diverse as Panera Bread, McDonald’s, and Taco Bell announced they have removed—and are continuing to eliminate—various additives to one degree or another.

While there’s been debate over the impact of engineered ingredients on humans, there’s no marketing downside in giving customers something they want. And experts say many Americans view additives as unhealthy and, as a result, of lower quality.

“It’s clear that consumers want to see this idea of clean labeling,” says Elizabeth Friend, strategy analyst at market research firm Euromonitor International. “It’s really gotten to the point where it’s become something that has become expected of major chains.”

There is no official definition for “clean” like there is for “organic.” Instead, Friend says, it’s “sort of a subjective term—a catchall for saying there’s nothing bad in there.”

The emphasis that Chipotle has put on higher-quality ingredients is a standard that other operators are chasing. Even with its clean pedigree, that company has not stood still, removing genetically modified organisms (GMO) from its food in 2015.

Panera recently completed a two-year effort to remove all additives among its 450 food ingredients, reformulating 122 of them. Subway eliminated artificial flavors and colors, removed artificial preservatives from some items, and switched to serving chicken raised without antibiotics. Pizza Hut and Taco Bell removed artificial colors and flavors; Chick-fil-A will remove chicken given antibiotics from its supply chain by 2019; and McDonald’s initiated a number of changes, like removing preservatives in its chicken nuggets.

In most “clean” claims, the companies are referring to the food they cook, not soda and other beverages that may include artificial coloring and sweeteners or high-fructose corn syrup made with GMO corn.

For big companies, becoming cleaner can take years to accomplish. Not only do reformulated menu items have to have the correct taste and texture, but the supply chain must also be able to handle the new ingredients, and operators must be able to manage higher costs.

It’s not just bigger companies navigating the hurdles to a cleaner menu. Smaller operators also have their issues, like being able to make manufacturers provide them with what they want.

Blaze Pizza’s executive chef, Brad Kent, has focused on bringing in the cleanest ingredients possible since the Pasadena, California–based company launched in 2012. However, that wasn’t always easy at the beginning.

“Some ingredients weren’t available, like clean salami, pepperoni, and black olives necessary for a pizza place,” he says. But once the chain gained some critical mass, he says, it was easier to put pressure on manufacturers to take out additives like artificial nitrates and colors and chemical preservatives.

There’s often a collaborative effort between operators and manufacturers about new and existing products. “Sometimes we reach out and say we need something, but it can’t have high-fructose corn syrup, or sometimes they come to us with a nitrate-free item,” says Matt Marino, director of supply chain at Crushed Red, which is based in St. Louis.

Since a company like Crushed Red is focused on a clean menu, he adds, producers “know we’re always looking for these types of products, and as soon as they are available to them, we are the first they come to, because we will test them correctly.”

Meat supplier Hormel, for instance, launched its Natural Choice luncheon meats and noncured bacon a decade ago due to demand. This and some other Hormel lines include products with no preservatives or artificial colors or flavors, and they “are among the largest drivers of growth” for the company, says Annemarie Vaupel, who leads Hormel’s foodservice innovation team.

“We spend a lot of time in operators’ kitchens gaining insight into what they want,” she says.

The Natural Choice line has only meat, water, sugar, and salt, and high-pressure processing is used to protect the products, with water replacing preservatives like nitrates. Vaupel says the taste and texture of these items are the same as the originals, except for some differences with meats that are normally cured, such as bacon.

The additive-free meats are also slightly pricier. “There is a difference, because natural sugar and sea salt tend to be more expensive than synthetic ingredients,” she says. But consumers are also willing to pay extra for a cleaner item.

Blaze and Crushed Red are part of a wave of pizza concepts stampeding to join the clean-label club.

“Everything on our savory line is clean,” says Blaze’s Kent, noting that it accomplished that feat earlier this year. Nitrates have been removed, as has artificial coloring; for example, the coloring that turns olives black was replaced with a process that makes the fruit brown and not noticeably different on pizza.

The biggest nut to crack has been banana peppers, which are sensitive to texture and color loss during time-consuming shipping. Blaze was able to find an American producer of natural banana peppers. “It’s not shelf stable, but that’s OK with us,” Kent says, adding that the company goes through ingredients quickly.

Crushed Red also began with a very clean menu and has added new items as they’ve become available. “Things like high-fructose corn syrup have been avoided since the beginning,” Marino says. “As we develop new products, nutrition and the quality of ingredients have always been at the forefront.”

There are no artificial ingredients in any of the chain’s salads. The produce is sourced locally when possible but is not organic because the supply is “pretty inconsistent,” he says. However, salad dressings are organic, the corn is GMO-free, and meat is from hormone- and antibiotic-free chickens.

Late last year, Columbus, Ohio–based pizza chain Donatos completed an 18-month process to eliminate all artificial colors and flavors and high-fructose corn syrup from its pizzas, salads, and submarine sandwiches. Sixteen ingredients needed to be replaced.

“The ingredients and what we provide customers have always been important and part of our story,” says Donatos chief executive Tom Krouse. “We’ve had fresh-cut vegetables since the beginning, and freshly cut salads. It’s not a marketing tactic.”

It took three years to find a banana pepper without additives that matched the flavor, color, and texture of the company’s original ingredient. “We wanted to improve the nutritional value while retaining the taste of Donatos,” Krouse says. “I can tell you unequivocally that there is no flavor change.”

The company also eliminated potassium bromate used to whiten and strengthen dough, and is working to reduce sodium. “There will always be a list of things to improve on because of advances in technology, or supply will make it viable,” Krouse says.

Having as clean a menu as possible is part of the overall ethos at San Francisco–based Mixt, which was named one of the Bay Area’s greenest restaurants by an organization that helps eateries improve their environmental practices.

“When we started 12 years ago, which seems like a long time ago, we wanted to be very transparent with our customers about the type of food we were offering,” says chief executive Leslie Silverglide. “We were pushing the bar, not just where we were sourcing from, but in our strict rules about sourcing [healthful food].”

The ingredients—sustainable, non-GMO, and mostly local and organic—are featured in salads, grain bowls, and sandwiches. “You can really taste the difference with food that is fresh, like local, organic lettuce compared to a bag of greens that are gassed” with added carbon dioxide and nitrogen as a preservative, Silverglide says.

Clean eating also means serving meats without additives, so the chicken is free-range with no antibiotics or hormones and the beef is grass-fed. Further, any sweetening agents are from cane sugar, agave, or honey.

Featuring clean meats is the mantra of several burger chains, too.

“We pride ourselves in using organic beef and chicken,” says Michael Berger, founding partner and vice president of supply chain at Elevation Burger, based in Falls Church, Virginia. “It’s been our founding principle.”

The bacon is antibiotic-free, as the organic version has become more difficult to find.

The beef is from humanely raised, antibiotic-free, grass-fed cattle grazing on land free of pesticides and chemicals. The sustainable protein is sourced from several countries “since there’s only so much organic beef available,” Berger says. Organic, free-range chicken is easier to source.

In addition to the meats, Elevation Burger uses numerous other additive-free ingredients. The cheese in its grilled-cheese sandwich uses six-month-aged unprocessed cheddar, and french fries are prepared in olive oil.

Despite the higher cost of organic meats and other clean ingredients, consumers are not shying away from the chain, which has grown to nearly three-dozen units in the U.S.

Company research shows “a third of our guests are directly responding to the … messaging about food’s characteristics,” Berger says. “We don’t go out of our way to call it ‘clean’ or ‘higher quality,’ or to pooh-pooh others. We just say, ‘This is who we are.’”

Golden, Colorado–based Good Times Burgers & Frozen Custard features burgers made with Meyer Natural Angus beef that is free of antibiotics and added hormones, raised humanely on a diet of grasses, and supplemented by feeds containing grasses and grains.

“All of our beef is ‘never-ever,’” says Boyd Hoback, chief executive, referring to the U.S. Department of Agriculture term that signifies no growth implants, no antibiotics, and no animal byproducts in the feed. “It’s been that way for years.”

The company added Springer Mountain Farms natural chicken in 2012. Unlike the beef, which retained its similar blend when shifting to the natural meat, chicken was more difficult to get the right texture, flavor, and moisture for hand breading, Hoback says.

Bacon is a different story, because the natural variety doesn’t work from a financial standpoint, and “bacon eaters are less sensitive to the all-natural part of it,” he says. But natural beef and chicken “is a big differentiator. There aren’t many others who have taken that position.”

New York’s Between the Bread, which has three eateries and a thriving catering business, has had an interest in providing clean, high-quality, local, and natural food since opening in 1979, says partner Jon Eisen. Its chefs prepare daily specials and rotate its vegetables and grains monthly.

For instance, turnips, which can be farmed during the winter in the Northeast, are the monthly veggie for January, while cucumbers and tomatoes are in season in the summer.

“The way our relationship works with vendors is we have an overwhelming preference for local products,” he says. “Instinctively, consumers know local is better tasting, cleaner, and sustainable.” But guests also would rebel if some dishes, like the kale salad, were removed because of seasonality. So kale comes from California in the winter.

The most popular protein at Between the Bread is salmon, and that is sourced from fish farms in the Faroe Islands between Iceland and Scotland. “We spent countless hours of research on how to get the cleanest and most natural salmon,” Eisen says. “We looked at Chile, Canada, and elsewhere, and we think this is the best.”