His colleague, a Romanian émigré named Mihai Niculescu, 37, came up with the mirror idea by marrying his own specialty in business marketing, known as behavioral choice, with research done by others on self-image. Over a fully loaded Mexican meal at the famed L & J Cafe here, he said his own sizable belly gave him an insider’s edge when studying the marketing cues that lead to overconsumption. “Eating this, I don’t realize I’m overweight, until I look at myself,” he said.

A paper the two men wrote last year for The Agricultural and Resource Economics Review said the conventional methods promoted in Washington and elsewhere to encourage Americans to eat more fruits and vegetables have either failed, or require taxpayer money at a time when food stamps are at political risk. These efforts include ads and store display signs promoting produce as healthful, and reducing its cost through tools like additional vouchers for low-income women.

By contrast, Mr. Payne and Mr. Niculescu are pursuing a strategy that behavioral scientists call nudge marketing, an idea popularized by the 2008 book “Nudge,” by the former Obama administration regulatory affairs administrator Cass R. Sunstein and the University of Chicago professor Richard H. Thaler.

Nudge marketing calls for applying just the right amount of pressure to persuade: not too little, not too much. In the El Paso grocery trials, using both the green arrows on the floor with the green placards in the carts caused produce sales to fall.

“It nudged too hard,” Mr. Payne said.

By several measures, El Paso is one tough testing ground for these studies. Thirty-two percent of the city’s adults are obese, and 12.2 percent have diabetes, exceeding the statewide average, according to Texas health department estimates. The fast-growing Hispanic population has become a favorite marketing target for processed-food manufacturers.

Much of that was evident at the Lowe’s store where Mr. Pulido and other shoppers encountered the mirrors. Many of its customers are significantly overweight, and gravitate toward the chip and soda aisles. As in many supermarkets, the store’s produce section, while decently stocked with eye-pleasing displays, gets only about 10 percent of the total space and none of the prime real estate that drives the most sales: the front-of-the-store display towers, which companies rent from the store, and spots by the checkout lanes.

“That’s Frito-Lay, that’s Frito-Lay, that’s Frito-Lay,” said the manager, Gloria Narro, spinning around in the center of the store to point out all the displays for that company’s snacks. “We’re all trying to eat healthier, but there’s so much competition for us,” she said. “Right next door is a store known for its fresh meat. Walmart is down the street. Walgreens and CVS just opened up, carrying whatever you need in food.”