Knowing the calorie content of foods does not help people understand which foods are healthier, according to a study I recently co-authored in the Journal of Retailing. When study participants considered calorie information, and healthy food as less healthy. They were also less sure in their judgments.

In other words, calorie labeling didn’t help participants judge foods more accurately. It made them second-guess themselves.

Across nine experiments with over 2,000 participants, my colleague and I tested how people use calorie information to evaluate food. For example, participants viewed food items that are generally deemed healthier, such as a salad, or ones that tend to be less healthy, such as a cheeseburger, and were asked to rate how healthy each item was. When people did not consider calorie information, participants correctly saw a big gap between the healthy and unhealthy foods. But when they considered calorie information, those judgments became more moderate.

In another experiment in the study, we found that asking people to estimate the calorie content of food items reduced self-reported confidence in their ability to judge how healthy those foods were − and that drop in confidence is what led them to rate these food items more moderately. We observed this...