Kids don't want to eat their veggies because their parents tell them to do so. They want to eat them because they think their friends are eating them. That was the theory behind a University of Minnesota study, which examined whether images of beans and carrots on lunch trays would increase student consumption of those vegetables.

"Kids, they don't want to do what they're told," said Traci Mann, a psychologist and one of five U of M faculty members leading the study. "Tell them to eat their vegetables? Forget about it."

It appears that the U of M researchers were right on. In a study published in the Journal of the American Medical Association, the researchers found that students at a Richfield elementary school selected and ate more beans and carrots when their trays had pictures of those vegetables on them.

The researchers monitored a typical day at the school cafeteria -- counting how many students selected vegetables and then weighing the vegetables thrown away in order to determine how much the kids consumed. (Mann said it was a painstaking process of collecting every scrap of leftover veggie from the trash, floors and tables.) They then did the same exercise on a day when the trays had vegetable images on them, like this: 

On the typical day, 42 students took green beans. Each student who took beans ate about 19 grams of them. On the study day, 96 students took beans; each student who took them ate about 19.1 grams.

On the typical day, 77 students took carrots. Each student who took carrots ate about 31 grams of them. On the study day, 238 students took carrots; each student who took them ate about 27.1 grams.

Mann said she believes the pictures created a new social norm for the students, by which they believed putting veggies in the designated spots was what they should do and what their friends would be doing.

The U of M team -- which includes professors in marketing, applied economics and food science -- tested several different ways to "nudge" students at the Richfield school to eat more veggies. In one instance, they tried moving vegetables to the front of the food line. In another instance, they had the lunch lady offer verbal encouragement to each student to try vegetables. Results of those efforts haven't been published yet, but Mann said she had been most excited about the potential of putting images on tries because it was so subtle.

"I was much more hopeful for this kind of nudge," she said, "when the students did not feel like they were being pushed into doing something."

The idea came from a separate study in which researchers tested if shoppers would buy more fruits and vegetables if their grocery carts included special sections in which to place produce. Mann said she couldn't find any prior studies using this approach with school lunch trays before. Here are the specific study results:

The study results showed that three times as many student took carrots when their trays had pictures of carrots, but that the average amount consumed actually declined. This means that the students who always took carrots probably ate their usual amount, but that the students who took them for the first time ate less of them. Even so, the numbers suggest that the first-time students at least ate some of the carrots. And Mann said that is a critical first step toward healthier eating habits for the kids.

"The more you have a bite or two of a carrot," she said, "the more you're going to slowly start to get used to the taste."

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