The fast-food industry is suddenly embracing an unlikely new ingredient

Forget burritos and burgers - today, vegetables are the hottest trend in the fast-food industry.

Vegetables are exploding on the menus of fast-food and fast-casual chains, from greasy omnivore favorites like Taco Bell to new vegan concepts like By Chloe.

"We're going to see more vegetables," Panera's head chef Dan Kish told Business Insider.

"We're going to see culinary treatments of those vegetables in ways that bring out their flavors without adding a lot of other things to it - so keeping things as natural as possible. Upping the percentage of vegetables in your diet - [it] is part of our job to help you with that."

Ironically enough, Kish brought up the rise of vegetables at an event promoting the launch of the chain's new and improved bacon. However, in the modern chain-restaurant landscape, meat and vegetables are increasingly living in harmony on menus.

Kish says that Panera is aiming to balance meat-centric options, like a bacon-turkey sandwich, by packing more vegetables into the dish.

On the other hand, Taco Bell, a chain hardly known for sustainability and nutrition in the way that Panera is, has a slightly different approach that's similarly packed with vegetables. The Mexican chain emphasizes customization, and customers' ability to make almost any dish meat-free. Last year, Taco Bell debuted a vegetarian menu certified by the American Vegetarian Association, which allows customers to substitute beans and rice for meat in most menu offerings.

"Vegetarian has been really big for us recently," because of its relevance to millennials, Taco Bell's dietitian and product developer, Missy Nelson, told Business Insider earlier this year.

Even less vegetarian-friendly chains are realizing that vegetables may be key to success. While once iceberg lettuce and tired tomatoes were accepted as a forgettable garnish at chain restaurants, meat-centric chains are doubling down on veggie quality.

Both Chick-fil-A and McDonald's have ditched iceberg lettuce in recent years. Instead, the chains are testing vegetables such as kale and broccolini.

"They didn't feel iceberg lettuce was a nutritious green, and they didn't feel good about eating it in a salad," McDonald's corporate chef Jessica Foust told Business Insider in July.

Why are fast-food chains investing in vegetables, something that has long been seen as antithetical to their existence?

Part of the reason is customer demand: While only about 3% of Americans identify as vegetarian or vegan, an increasing number of people are cutting meat from their diets. According to a 2015 study, 26% to 41% of Americans report that they cut down on the amount of meat they ate in the past year.

Adding more vegetables to the menu is a great way to appeal to the average American, who may not be committed to a 100%-meat-free lifestyle, but wants to dabble in more veggie-friendly diet.

However, there is also a hidden financial bonus to focusing on beefing up vegetables offerings. Vegetables typically cost less than meat, meaning that adding more vegetables to a dish can provide a cheaper way to fill up customers.

Chefs Roy Choi and Daniel Patterson have made headlines with the concept Loco'l. The concept provides healthy meals at fast-food prices by cutting costs by doing things such as adding more grains and vegetables to chain standards like burgers. Customers fill up faster, and the company is able to save money while also providing a healthier meal.

As old-school chains explore their vegetarian options, Loco'l isn't the only new concept banking on vegetables. 

By Chloe, a new 100%-vegan chain, only opened its first location a year ago, in New York City.

Now the chain has a location in Los Angeles opened in partnership with Whole Foods 365, a recently opened sweets shop, and several more new locations in development. On Friday, the chain announced it was adding two new vegan contributing chefs to the organization, Jenné Claiborne and Laura Kretzer.

By Chloe doesn't offer any meat or meat-byproducts on the menu. However, the vegan chain has some surprising similarities to fast-food chain in its approach to vegetables.

According to the company, more than 80% of customers are not even vegetarian. In fact, a number of customers don't even realize that the concept is vegan when they order their food.

This notion, that vegetable-based food is appealing to nonvegetarians, is the very same idea responsible for the rise of vegetables in fast food. In 2016, veggies aren't just for vegetarians - they're also for all types fast-food lovers.