Next time you reward a child with a treat, consider offering fruit, nuts or a cereal bar instead of ice cream or candy, a Cornell economist suggests.

Research by an international team including Michèle Belot, professor in the Department of Economics, found that children valued a sweet food more after receiving it as a reward. In a second experiment, rats rewarded with sugar pellets for completing tasks consumed significantly more calories over a 24-hour period than a control group.

Together the studies – the first to investigate how using food as a reward affects its valuation – offer preliminary evidence that calorie-dense sweet rewards could be a contributing factor to obesity, the researchers said.

“It is perhaps worth thinking twice about what one uses as a reward, and considering healthier alternatives,” said Belot, the principal investigator for the child study. “We understand that people like treats, but whether they have to be associated with rewarding behavior is a different thing.”

Belot, who has a joint appointment in the School of Industrial and Labor Relations and College of Arts and Sciences, is a co-author of “Rewarding Behavior with a Sweet Food Strengthens its Valuation,” published April 14 in Plos One.

Additional authors are Jan Bauer, associate professor at Copenhagen Business School in Denmark; Marina Schröder, professor at Leibniz University Hannover in Germany; Martina Vecchi, assistant professor at Pennsylvania State University; Tina Bake, a postdoctoral research fellow at the University of Gothenburg in Sweden; and Suzanne Dickson, professor at the University of Gothenburg and principal investigator for the rat study.

The team first assessed how children valued a range of snacks, from crackers and rice cakes to grapes, dried apricots and yogurt. For the study, they selected a sweet food with a mid-range valuation – dried apple slices, consisting of 56% sugar.

Working with more than 200 first graders ages 6 to 8 at several elementary schools in Cologne, Germany, they visited classrooms twice a week for a month. A control group of students was given the dried apple “for free,” without having to work for it. The rest received it as a reward for counting dots in pictures – two pictures in a “low-effort” group and 10 pictures in a “high-effort” group.

The researchers measured valuations of the dried apple (expressed in happy or sad emoticons) before the counting tasks began, after the four-week treatment period, and again four weeks later.

The study found that children who earned the apple as a reward valued it significantly more than those who received it unconditionally – eight percentage points more after a month of rewards, and 14 percentage points more a month after that.

“Those who had to work for the reward eventually valued the food used as a reward more than those who didn’t have to do anything at all for it,” Belot said.

There was little variation between the low- and high-effort groups, however, suggesting the amount of work needed to earn the reward wasn’t behind its higher valuation. A more likely driver, the researchers said, was the apple’s association with the positive experience of being rewarded, a process known in psychology as evaluative conditioning.

The higher valuation of sweet rewards might not be worrisome if it didn’t lead children to crave more sweets, or if those calories were offset by eating less other food, the researchers noted.

But at least among rats, the second experiment showed that wasn’t the case. Rats rewarded with sugar pellets for pressing a lever ate more of them over a three-hour period than rats that didn’t work for rewards, and had “a significantly higher calorie intake” over 24 hours, the study found.

“The results indicate that the increase in valuation of a reward leads to an increase in total calorie intake,” the authors wrote.

That, Belot said, raises concerns about potential long-term obesity effects.

The research team cautioned that the rats’ behavior does not necessarily translate to humans, that their findings in a school setting might not apply to households or different age groups, and that they couldn’t estimate the relative importance of sweet rewards among potential obesity risks.

Still, the scholars concluded, the combined studies “provide initial evidence for a causal link between the common practice of rewarding with sweet foods and multiple precursors for weight gain.”

The findings do not imply, Belot said, that the occasional ice cream treat will lead to obesity, or that parents and teachers should reward children with salads. But she said they should think more carefully about a range of rewards that don’t consist entirely of sugar, perhaps including fruit, dried fruit, nuts or cereal bars.

“There is a spectrum of foods that may be potentially experienced as rewarding,” Belot said, “but that are not completely unhealthy.”

The research was funded by a European Union Consortium Framework Program grant.