Burger King has its BK Veggie; Chipotle has its tofu sofritas. Now a school nutritionist from Pharr, Texas, is suggesting the unthinkable: that Texas chain Whataburger should join the fold and add a veggie burger to its menu.

Miguel Villarreal launched a Change.org petition asking Whataburger to offer "a plant-based entrée, like a veggie burger"; it has garnered 650-plus signatures in four days.

Villarreal, who is director of food and nutritional services at the Novato School District in northern California and director of wellness for Marin County, says that even a burger chain in the middle of meat country can see another way. "This is not about demonizing Whataburger, but making sure they're doing their part by offering an alternative," he says.

He's seen dramatic changes in his industry in the past 10 years as school districts grapple with rising obesity rates among children. "About eight years ago, I stopped serving highly processed red meat to our kids," he says. "Instead we've been serving veggie burgers and locally grown fruits and vegetables.

"But it's not just the schools. It's fast-food restaurants. I'm from South Texas, and I know about the high rates of chronic illness in the South. Whataburger has millions of loyal customers who do not all know that some of the food they're eating is making them sicker."

He links disease to obesity, causing illnesses such as diabetes, stroke and some cancers. According to a 2014 study called "The State of Obesity: Better Policies for a Healthier America," Texas' adult obesity rate is at 30.9 percent, up from 25.3 percent in 2004 and 10.7 percent in 1990.

Other chains have responded to the interest in plant-based food, says Ethan Dussault, director of the Texas office of The Humane League, a national animal-advocacy organization. "People are changing the way they eat to create a more humane and sustainable future," he says.

In addition to Burger King, Johnny Rockets and Red Robin both offer veggie burgers. Midwestern burger chain White Castle just introduced its trademark miniature square sliders in a veggie version made with the veteran Dr. Praeger's brand of veggie burger.

Whataburger's non-meat options are currently limited to a side garden salad. Villarreal is heartened by the fact that he's already received a short response from a Whataburger representative, who told him that the chain was open to new ideas.

"Whataburger and I have something in common," he says. "We both grew up near the Rio Grande Valley."