With the spotlight on childhood obesity, schools across the country are looking for ways to get kids to eat more fruits and vegetables. In New York, the Department of Health decided to do some research. How much, it wondered, would a school need to cut its prices for apples, oranges and bananas to increase sales by 5 percent over a year?

Brian Wansink was called in to play detective. But the director of Cornell’s Food and Brand Lab soon discovered he had been hired to answer the wrong question. Price wasn’t the problem. It was the presentation.

In the school cafeterias Wansink surveyed, whole fruits were displayed in steel bins in dimly lighted areas of the lunch line. Wansink went to discount store T.J. Maxx and bought a cheap wire fruit rack. He found an extra desk lamp, which he used to shine on the fruit. “Sales of fruit in one school went up 54 percent. Not in a semester: by the end of the second week,” Wansink said. “It would have gone up faster, but they kept running out of fruit.”

Nudging students

The debate about how to fix school lunch has, until now, focused largely on what is sold in schools: Public health advocates argue that french fries and cookies should be banned, and some schools have done just that. Food manufacturers and some parents retort that such deprivation will only encourage students to get their fix elsewhere.

Now, researchers such as Wansink are turning their attention to how school food is sold and to whether marketing and incentives can help fight obesity, often at little or no cost.

Federal regulators, charged with improving the school lunch program on a tight budget, are paying attention. Cass Sunstein, a leading behavioral economist and a co-author of the seminal text “Nudge: Improving Decisions About Health, Wealth, and Happiness,” is the administrator of the White House Office of Information and Regulatory Affairs. In April, the U.S. Department of Agriculture held a two-day conference on how behavioral economics can improve federal food policy. This fall, the agency will award $2 million to fund more research in the field.

The attractions are clear. Such solutions — sometimes called “nudges” — can be low-cost. They also are flexible. Although most people think of school lunch as a monolithic federal program, lunchrooms across the more than 14,000 U.S. school districts vary, and most decisions about what and how students eat are made locally. Most important, implementing change doesn’t require a vote in Congress.

Though Michelle Obama has made childhood obesity her signature issue, legislation that would increase funding for school lunch and boost nutrition standards remains stalled.

“These ideas offer a way to be more effective with the meals we are already serving,” said Joanne Guthrie, the USDA’s assistant deputy director for nutrition in food assistance and nutrition research.

“There’s a lot of talk about putting more whole grains and dark green vegetables in the lunchroom. But it may not be the best way to improve health unless we are sure the kids will eat them.”

Simple solutions

Wansink is a pioneer of food behavioral research. (His first book, “Mindless Eating: Why We Eat More Than We Think,” demonstrated how simple acts, such as eating from a smaller plate, can help reduce food consumption.) Wansink became interested in school food after a two-year stint in Washington working at the USDA’s Center for Nutrition Policy and Promotion. The controlled environment of school cafeterias and their often-perverse incentives — at a time when one-third of American children are overweight or obese, USDA guidelines continue to mandate calorie minimums but not maximums — is a perfect research laboratory.

Take payment options. Most schools accept debit cards or PIN numbers, which help the lines move faster and make it impossible to tell which students receive a free or reduced-price lunch. In a yet-unpublished study, Wansink and Cornell lab co-director David Just found that students who pay with debit cards are more likely to buy desserts and junk food, while those who pay cash tend to choose milk, water, fruits and vegetables.

The decision comes down to this: Would the student rather have a brownie or use the money later to buy music or movie tickets? “It introduces what we call a ‘pause point’ in what would otherwise be a mindless transaction,” Wansink said.

Wansink does not advocate an all-cash system. Instead, he says one solution might be to limit what students can buy with their debit cards. Parents might choose to follow recommendations, or they could set specific standards themselves: no peanuts, say, for a child with an allergy, or no desserts, period. Children who still want to buy a forbidden product would have to fork over the money themselves. Wansink calls the idea “cash for cookies.”

Researchers are also interested in the idea of incentives, many of them gobsmackingly simple. At a New York middle school, Wansink found that when the salad bar was moved to a prominent location near the cashiers, sales increased by between 200 and 300 percent.