A Dieting Conundrum: Why dieters underestimate calorie counts of meals

Based on the research of Alexander Chernev

Kellogg Insight
January 12, 2012

In the effort to combat the burgeoning problem of obesity, authorities such as the United States Centers for Disease Control and Prevention and the World Health Organization promote the benefits of healthy eating plans that include plenty of fruits and vegetables. Individuals concerned with their weight often internalize that message. But they frequently do so in an irrational way. According to research by Alexander Chernev, an associate professor of marketing at the Kellogg School of Management, many think that adding a “healthy” option, such as a side dish of celery and carrots, to a high-calorie meal such as a cheesesteak somehow reduces the meal’s overall calorie content.

Chernev’s research also gives the tale an added twist: the more serious that individuals are about dieting, he finds, the more likely they are to fall for this “side salad illusion.” “People often behave in a way that is illogical and ultimately counterproductive to their goals,” Chernev says. “We’ve shown that people on a diet are more likely to underestimate the calorie count of combinations of healthy and unhealthy meals.”

The Dieter’s Paradox

Information about the “dieter’s paradox,” as Chernev calls it, emerged from a nationwide study in which more than 1,000 respondents were asked to estimate the calorie count of a variety of meals. About half the respondents saw a series of unhealthy meals: a hamburger, a bacon and cheese waffle sandwich, chili with beef, and a meatball pepperoni cheesesteak. The rest saw these same unhealthy meals accompanied by a healthy item—a few celery sticks, a small organic apple, a small salad without dressing, and a side dish of celery and carrots, respectively.

Respondents who saw only the unhealthy meals estimated that they contained 691 calories on average. But those who saw those same meals accompanied by the healthy items assessed the average calorie count at just 648. For example, participants shown a bowl of chili rated it as averaging 699 calories; however, participants who viewed the same bowl of chili combined with a green side salad rated it as having only 656 calories. In every case the addition of the healthy food item led to the erroneous perception that the number of calories had decreased.

After the participants evaluated the calories in these meals, they were asked to indicate the extent to which they were concerned with managing their weight. Astonishingly, the data showed that the most weight-conscious individuals believed most strongly in the apparent ability of a healthy option to reduce the calorie content of an unhealthy meal. Those more concerned with their weight rated the unhealthy item paired with a healthy one as having 615 calories—96 calories less than dieters who rated the unhealthy item alone. People less concerned with their weight were not as susceptible to the side salad illusion. They estimated the unhealthy–healthy combination as having only 26 calories less than the unhealthy item alone (Figure 1).

Figure 1. Weight-conscious individuals are more likely to believe that adding a healthy option to an unhealthy meal decreases a meal’s calorie content.

“The fact that those most concerned with their weight are also more likely to underestimate the calorie content of a meal is counterintuitive,” Chernev says. “It also means that they will be more likely to overconsume and consequently more likely to gain weight.”

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