Marketing Jan 1, 2012

A Diet­ing Conundrum

Why dieters under­es­ti­mate calo­rie counts of meals

Based on the research of

Alexander Chernev

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.

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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.”

A World of Vices and Virtues 

What could cause this appar­ent­ly illog­i­cal behav­ior? Maybe dieters real­ly believe that healthy food items have neg­a­tive calo­ries — per­haps because the ener­gy need­ed to digest them exceeds their calo­rie con­tent. To test that pos­si­bil­i­ty, researchers asked a sep­a­rate group of respon­dents to esti­mate the caloric val­ue of the healthy foods in the main study. Not a sin­gle par­tic­i­pant believed the healthy items had neg­a­tive calories.

The data show that the dieter’s para­dox is not caused by people’s beliefs that healthy items like broc­coli have neg­a­tive calo­ries,” Chernev points out. Instead, he argues, the dieter’s para­dox stems from a fun­da­men­tal flaw in the way we think about food health­i­ness and its impact on our weight.

This black-and-white view of foods is the key dri­ver of people’s ten­den­cy to under­es­ti­mate the calo­rie con­tent of meals com­bin­ing virtues and vices.”

Peo­ple think of food in terms of vice and virtue — healthy and unhealthy,” Chernev explains. The eas­i­est way to diet is to cat­e­go­rize into good and bad; you aim to min­i­mize the bad and max­i­mize the good. The more you want to lose weight, the more like­ly you are to cat­e­go­rize foods into vices and virtues. So when we add some­thing healthy to an unhealthy food, we think it makes the entire meal health­i­er. And because we often con­fuse a meal’s health­i­ness with its calo­rie con­tent, we think that health­i­er meals are also more diet-friend­ly. Hence, we assume that the vice/​virtue com­bi­na­tion is not only health­i­er but also has few­er calo­ries than the vice alone.” In oth­er words, he adds, virtue makes the vice seem less vicey.’ ”

Those most con­cerned with man­ag­ing their weight are also more sus­cep­ti­ble to these errors in judg­ment, Chernev says. Because the side sal­ad illu­sion stems from our ten­den­cy to stereo­type foods into vices and virtues, it tends to be more preva­lent among indi­vid­u­als most like­ly to invoke such stereo­typ­i­cal think­ing. Many dieters fall into that category.

This is because most nutri­tion­al guide­lines, as well as many diets, focus on pro­mot­ing the con­sump­tion of cer­tain food groups while advo­cat­ing reduced con­sump­tion, or even avoid­ance, of oth­ers,” Chernev says. And although par­tic­u­lar guide­lines and diets vary in the type of foods and nutri­ents they con­sid­er accept­able or unac­cept­able, most share the under­ly­ing prin­ci­ple of cat­e­go­riz­ing foods into virtues and vices. This black-and-white view of foods is the key dri­ver of people’s ten­den­cy to under­es­ti­mate the calo­rie con­tent of meals com­bin­ing virtues and vices.”

A Bal­anc­ing Act Beyond Dieting 

This bal­anc­ing act is not unique to diet­ing. We show the same effect with prices. When you add some­thing inex­pen­sive to an expen­sive item, peo­ple often assign less val­ue to the com­bi­na­tion than to the expen­sive item alone,” Chernev says. The same thing is like­ly to hap­pen with the dura­tion of time, when you com­bine short inter­vals with long intervals.”

Chernev, who reports that I’m not on a diet, but I add healthy options to my meals,” is the author of the book The Dieter’s Para­dox: Why Diet­ing Makes Us Fat. In it he argues that try­ing hard­er to achieve such goals as man­ag­ing our weight does not nec­es­sar­i­ly make us smarter when we choose the means to pur­sue those goals. As evi­denced by dieters’ ten­den­cy to under­es­ti­mate the calo­rie con­tent of their meals by com­bin­ing virtue and vice options,” he says, greater moti­va­tion often leads to out­comes that are coun­ter­pro­duc­tive to our goals.”

Sim­i­lar think­ing applies to pub­lic pol­i­cy­mak­ers. Pro­vid­ing healthy options is not a solu­tion; it’s part of a solu­tion,” Chernev asserts. What you real­ly need to pro­vide peo­ple with is not just infor­ma­tion, but knowl­edge on how to make deci­sions.” Thus, any strat­e­gy to improve calo­rie counts should focus not on the types of food we eat, whether vir­tu­ous or vice-rid­den, but on the quan­ti­ty con­sumed. The goal should be to cut the burg­er in half,” Chernev advis­es, not add a sal­ad to it.”

Relat­ed read­ing on Kel­logg Insight

Be Good, Get Mad: Exert­ing self-con­trol makes peo­ple more inclined to anger

Are Restau­rants Real­ly Super­siz­ing Amer­i­ca? Restrict­ing restau­rant meals may not trim Amer­i­cans’ expand­ing waistlines

About the Writer

Peter Gwynne is a freelance writer based in Sandwich, Massachusetts

About the Research

Chernev, Alexander. 2011. “The Dieter’s Paradox.” Journal of Consumer Psychology. 21(2): 178-183.

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