This basic idea about how humans come to like novel foods, surprisingly, doesn’t come up very much in discussions about the price of healthy eating—a topic that economists, public-health researchers, and journalists all disagree about. On one side there are a number of economists who say that on a per-calorie basis, it’s more affordable (not to mention less time-consuming) to buy fast food than it is to cook a meal using fresh produce. On the other side are those who maintain that thinking by the calorie doesn’t make sense, because Americans eat too many calories anyway. This latter group, which includes other economists as well as the food writer Mark Bittman, insists that it’s not all that difficult to cook a filling, nutritious meal for less money than it takes to go to McDonald’s, as long as one isn’t hung up on buying organic or local food.

Both arguments have their virtues and their shortcomings, but both overlook the basic fact that food purchased is not necessarily the same as food consumed. When many economists estimate the price of eating fresh foods, the cost when a child eats half of a 50-cent carrot is recorded as 25 cents, even if the other half goes to waste.

Could this unaccounted-for cost be part of the explanation for why high-income and low-income Americans tend to have different diets? Caitlin Daniel, a doctoral student in sociology at Harvard, recently published a study in the journal Social Science & Medicine suggesting that this cost might actually be large enough to change the shopping decisions of some low-income families, but small enough for wealthier parents to shrug off. In other words, richer parents might have plenty of room in their budgets to force brussels sprouts on their children 10 times and throw out what remains, while poorer parents tend to stick to dependable but less-nutritious foods that their kids are known to like.

Daniel arrived at this finding after interviewing 75 Boston-area parents from a range of economic backgrounds about their food-shopping habits. She spent an average of two hours with each interviewee, and followed a number of them on their trips to the grocery store. (And apparently, having a sociologist looking over their shoulder with a notepad didn’t deter the research subjects from their usual shopping behavior: Daniel reports that three interviewees stole from the grocery store even though they knew she was watching.)

The data that came out of Daniel’s study is qualitative, but it provides some insight into how parents of different economic backgrounds think about the costs of feeding their children. “I try not to buy things that I don’t know if he’ll like because it’s just, it’s a waste,” one lower-income mother told Daniel. Parents talked about wanting to serve “real” food, but out of necessity resorting to more dependable, easier-to-love foods such as frozen burritos or Hot Pockets. Whether the rejected food was eaten by another family member, stashed in the fridge, or thrown out entirely, parents mentally counted it as a loss.