Jason Koski/University Photography

Behavioral economists Brian Wansink, left, and David Just discuss nutrition with students at Beverly J. Martin Elementary School in Ithaca, N.Y.

School cafeterias that accept only electronic payments may be inadvertently promoting junkier food and adding empty calories to student diets, which contribute to obesity, say Cornell behavioral economists in the journal Obesity, Sept. 23.

Increasingly, schools use debit cards or accounts for cafeteria lunch transactions, write David Just and Brian Wansink, professors at the Cornell Center for Behavioral Economics in Child Nutrition Programs. To expedite long lunch lines and enable cleaner accounting, about 80 percent of the nation’s elementary and secondary schools have implemented debit systems that parents can add money to at any time.

“There may be a reason for concern about the popularity of cashless systems,” say the researchers. “Debit cards have been shown to induce more frivolous purchases or greater overall spending by adults and college students.”

Just and Wansink compared purchases at school cafeterias that use debit-only systems with those that accept debit or cash. They found that students at debit/cash cafeterias consumed about 721 calories compared with 752 calories at debit-only schools.

For non-healthy food items alone – such as candy, dessert, cheeseburgers and fries – students at debit-only schools consumed 441 calories during their lunch, compared with 378 calories for students at debit/cash schools.

An ice cream sandwich here and a bag of potato chips there add up: A child can draw down debit accounts quickly, the research points out. Parents pay for several weeks’ worth of lunches in advance, often with little control over individual transactions. Parents often have difficulty gauging how long the money should last, if spent wisely.

“This may lead children to generally greater spending on lunch,” the researchers report.

The results, the researchers add, have important implications for schools and child obesity. A small number of schools have introduced debit systems that allow parents to regulate daily spending, which can help combat the problem. If the use of cash, as opposed to debit cards, can nudge a student into making slightly healthier choices, then perhaps a “cash-for-cookies” policy, for example, would “encourage students to think twice before making their selection,” said Just and Wansink.

The study, “School Lunch Debit Card Payment Systems Are Associated With Lower Nutrition and Higher Calories,” was supported by the U.S. Department of Agriculture.