Why Wendy's and McDonald's Still Don't Have Veggie BurgersTwo of America's Big 3 burger chains are under pressure to add a meatless burger to their menus.

Update: As of May 4, Wendy's has beguntesting a veggie burgerin Central Ohio.

Vegetarians are constantly complaining about the lack of meatless fast-food options. So, if the market is there, why aren't more chains frying up veggie burgers?

The latest target for veggie-burger lovers trying to get a fast-food fix is Wendy's. A Change.org petition started byJackassstar Steve-O urging Wendy's to begin serving a veggie burger has gained nearly 13,000 signatures.

"We have witnessed some of the top fast food chains in the United States add hearty meatless alternatives," readsthe petition. "Burger King has had a flame grilled veggie burger for years, Subway has a veggie patty and is testing other options in different regions, White Castle now has veggie sliders, and Chipotle's tofu sofritas are popular among my vegan, vegetarian, and meat-eating friends and family."

如果你喜欢像我一样蔬菜汉堡,请签署my petition for Wendy's to add one now:http://t.co/O539whNMXqpic.twitter.com/i29Ve5Iwqz

— Steve-O (@steveo)April 28, 2015

The comedian also links to a popular petition for a meatless option at McDonald's that has gained more than100,000 signatures. However, the petitions haven't had much affect on the fast-food chains' menus.

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"Wendy's has a history of offering menu options to meet a wide variety of consumer preferences," Wendy's chief communications officer Liliana Esposito toldEntrepreneur."We recognize that many consumers are interested in vegetarian protein options as well, and we're constantly testing new menu items both domestically and internationally to serve local consumer tastes."

With thousands of customers apparently salivating for a veggie burger, it seems strange that two out of the three biggest burger chains in America aren't jumping on the chance to meet the demand. The one exception: Burger King.

Burger King began serving veggie burgers in 2002, partnering with Morningstar to become the first national chain to sell a vegetarian burger. Today, it's a permanent part of Burger King's menu, sold across the U.S.

While the veggie burger has cultivated a strong enough customer base to stay on Burger King's menu, the sandwich hasn't been in the spotlight recently. Instead, Burger King has slimmed down the menu and turned to new products and limited-time-offerings such as the Spicy BLT Whopper to spark momentum and sales. The last time a new Burger King veggie burger hit the market was in 2013, as part of a limited time "burger fest" menu that also included a turkey burger and aChipotle chicken sandwich.

Ultimately, chains' biggest fear when considering adding veggie burgers and other health-conscious options to the menu is that customers signing petitions won't actually show up to buy the products. The fear is justified: McDonald's tested veggie burgers in the U.S. in theearly 2000s, but the item simply didn't sell. Salads only made up2 to 3 percent of McDonald's U.S. salesin 2013, even as customers petitioned the chain for healthier choices.

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McDonald's responses to customers seeking the McVeggie hints at these issues:

"No, we don't currently sell veggie burgers. Although, we are always looking to evolve our menu," reads the company's webpage dedicated to answering the question. In another section of the company's "Our Food, Your Questions" website, the company states that menu items are tailored to countries' overall taste preferences, which is why the McVeggie is available in countries such as India, Germany, Greece and Dubai.

The lack of veggie-hungry customers is not a McDonald's specific problem. Less than a year after Burger King introduced "better for you"Satisfriesin 2013, the majority of franchisees hadcut the item, which is now no longer on the national menu. While customers may say they want meat-free and healthier choices, these concerns tend tomatter lessin actual restaurant situations.

If McDonald's or Wendy's truly believed that there was a market for a fast-food veggie burger in the U.S., there is no reason to believe the companies would not immediately add the burger to the menu. Beef prices are hitting record highs, making veggie burgers an economically viable alternative if customers bite. McDonald's especially is currently willing to try new types of protein, with the company's new "Create Your Taste" platform focusing in part on premium chicken. If McDonald's believed there was demand for the McVeggie, now would be the time to begin testing it on menus across the U.S.

However, customers need to prove that the demand is there. So far, thousands of signatures on petitions haven't translated into proof of demand for McDonald's or Wendy's. So, it may be time for vegetarians to take a different tack to proving their worth to burger chains. One possibility: start flooding Burger King with orders for the veggie burger. If there is one thing fast-food companies can't stand, it's the competition winning out.

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