One of the most peculiar findings in obesity research is that exercise — even if vigorous and regular — doesn’t reliably lead to weight loss. The reason, as I wrote last year, has to do less with physiology than psychology: people who exercise tend to reward themselves with desserts and snacks that they would never consume otherwise. Exercise helps you stay fit, but it also makes you hungry, so it usually doesn’t turn fat people into thin people. Call it the paradox of the gym.
A new paper just published in the Journal of Consumer Psychology offers another weight-loss conundrum: if you show people a plate of unhealthy food — say, a burger and fries — and then add some steamed broccoli to the same plate, most people will say the second plate holds fewer calories, even though it demonstrably has more food on it. The author of the new paper, Alexander Chernev of the Kellogg School of Management at Northwestern University, calls this “The Dieter’s Paradox.” (More on Time.com: See a special report on overcoming obesity)
Chernev begins his paper with a great question: Why, after 20 years of public outcry about obesity — federal, state, and local government spending on weight-loss programs; widespread media coverage of what is routinely called the obesity “epidemic”; the opening of tens of thousands of new gyms since the 1980s — why, after all this, do we keep getting fatter?
One reason, according to Chernev, is that people think that if they eat an apple, they are entitled to eat a pack of potato chips. “People behave as though healthy foods have halos,” he writes. “Because healthier meals are perceived to be less likely to promote weight gain, people erroneously assume that adding a healthy item to a meal decreases its potential to promote weight gain.”
Chernev has found that this misperception is actually stronger among those of us who are more weight-conscious. In an online experiment, he asked 934 people to estimate the caloric content of four meals. Roughly half were shown unhealthy meals: bacon-and-cheese sandwiches; meatball-and-pepperoni cheesesteaks. The other half were shown the same meals with a healthy side item: celery sticks, say, or an apple. (More on Time.com: The ‘Other’ Salt: 5 Foods Rich in Potassium)
Respondents estimated the first meal at 691 calories; they estimated the one with the healthy side item at 648 calories. Those who considered themselves weight-conscious were even worse at estimating the calories, according to the study. “Adding a healthy option decreased the perceived calorie content of the combined meal by an average of 96 calories for weight-conscious individuals but only 26 calories for those less concerned with weight,” Chernev writes.
These findings have major implications for how we conduct weight-loss programs: encouraging people to eat more vegetables may be the wrong strategy. Just as people reward themselves with a muffin after they go to the gym, they will reward themselves for eating some celery with their French fries. A better approach may be to persuade people to stop at certain intervals during meals to ask themselves if they are full. As Chernev writes, “the negative calorie illusion [is] less pronounced when individuals pay attention to the quantity of the combined items instead of focusing on the healthy/unhealthy aspects of the items.”
In other words, eat the cheeseburger if you want it. But don’t think that a side of steamed kale will make it better for you.