Why Looking at Overweight People Makes Us Want to Eat More, Not Less

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UpperCut Images / Keith Brofsky

Viewers of The Biggest Loser would probably agree that watching the weight-loss show fills them with inspiration. Seeing the obese contestants struggle should motivate us to eat better, exercise and lose weight too. Turns out, however, that premise is only half right — at least according to a new study that finds that people may actually eat more after seeing overweight people.

“Seeing someone overweight leads to a temporary decrease in a person’s own felt commitment to his or her health goal,” wrote study authors Margaret C. Campbell and Gina S. Mohr of the University of Colorado at Boulder (which is incidentally the most active city in the U.S.).

But why? It has to do with stereotype “activation,” the study says. When people are exposed to members of groups who have stereotypes attached to them, good or bad — like fat people eat a lot, or Asians are good at math — they become more likely to act in a way that’s consistent with that stereotype. “For example,” the authors write, “college students’ scores on general knowledge questions increased after exposure to a professor but decreased after exposure to a supermodel.” That’s true even if the stereotyped behavior is negative, and even if it goes against the person’s own values.

(More on TIME.com: “Can a Mother’s Pregnancy Diet Influence Her Child’s Future Weight?”)

That theory falls in line with a phenomenon that recent studies have designated the “contagion effect” of obesity, which suggests that people who have fat friends are more likely to gain weight too. TIME reported on the seminal 2007 study by Dr. Nicholas Christakis, a professor of medicine at Harvard Medical School, and James Fowler, a political scientist at University of California, San Diego:

According to their analysis, when a study participant’s friend became obese, that first participant had a 57% greater chance of becoming obese himself. In pairs of people in which each identified the other as a close friend, when one person became obese the other had a 171% greater chance of following suit. “You are what you eat isn’t the end of the story,” says Fowler. “You are what you and your friends eat.”

The obvious question is, Why? Spouses share meals and a backyard, but the researchers found a much smaller risk of gaining weight — a 37% increase — when one spouse became obese. Siblings share genes, but their influence, too, was much smaller, increasing each other’s risk 40%. Fowler believes the effect has much more to do with social norms: whom we look to when considering appropriate social behavior. Having fat friends makes being fat seem more acceptable. “Your spouse may not be the person you look to when you’re deciding what kind of body image is appropriate, how much to eat or how much to exercise,” Fowler says. Nor do we necessarily compare ourselves to our siblings. “We get to choose our friends,” says. “We don’t get to choose our families.”

(Incidentally, the contagion effect also works with weight loss, quitting smoking and happiness, Christakis and Fowler found.)

The current study suggests a different reason for the effect — activation of social stereotypes versus confirmation of social norms — which means that you don’t need overweight people in your close social network to influence your behavior. Even a fleeting glance of an unknown overweight person — which occurs more than you probably notice, considering that 67% of the U.S. population meets the clinical definition of overweight or obesity — might trigger stereotypically overweight behaviors like overeating.

(More on TIME.com: “Health-Washing: Is ‘Healthy’ Fast Food for Real?”)

Campbell and Mohr put together a series of five experiments to determine the impact of the mere sight of an overweight person. In the first, the researchers recruited people walking through a lobby on campus, and showed them pictures of either an overweight or normal-weight woman, or a lamp. The respondents, average age 25, were asked to rate the photos for a future studies (a sham task), and then were allowed to help themselves from a candy bowl as a “thank you” for their time.

Those who saw the photo of the overweight woman took significantly more candy (an average 2.2 pieces) than those who saw the normal-weighted woman or the lamp (an average 1.5 pieces).

The researchers’ subsequent experiments involved “cookie taste tests.” As in the first experiment, participants were first primed with photos of either overweight or normal-weight people, or a neutral image like a tree. Then they were asked to rate cookies by tasting at least one (but up to eight) cookies presented on a plate. People who gazed at pictures of the overweight woman ate significantly more cookies than those who were exposed to the thinner woman. The difference held up regardless of the participants’ gender or weight.

Interestingly, however, there were certain factors that interfered with the fat person-induced overeating. One involved using pictures of overweight people actually eating. Although participants ate more cookies after viewing simple portraits of overweight people, they ate fewer when shown overweight people eating. The difference is that the former condition only activates a stereotype — likely unconsciously — while the latter more overtly establishes a link between eating and weight. “It may be necessary for attention to be distracted from the person’s weight,” the researchers write. “If a consumer considers stereotype membership (e.g., “that person is overweight”), the stereotype effect on…behavior may be attenuated.”

(More on TIME.com: “Beware the Office Candy Bowl”)

Another way researchers kept people from eating more: simply reminding them of their own health goals. When study participants were asked to write for three minutes about their health goals (versus their home state) before eating cookies, they ended up eating the same amount regardless of whether they viewed a portrait of an overweight or thin woman.

“The findings of our research are consistent with the spread of overweight through social networks,” concluded the researchers, whose study was published in the Journal of Consumer Research. “People see, both in person and in photos, the people with whom they have close social ties. When close others are overweight, our research suggests that stereotype activation could lead to increased food consumption relative to when close others are healthy weight since merely seeing someone overweight can increase eating.”

Back to The Biggest Loser. Whether the show helps prompt healthier behaviors in viewers may depend on which segment they watch. If you’re tuning in only for the end-of-show weigh-ins, maybe not. But if you’re also watching the contestants eat and exercise for weight loss, it might actually be good motivation.

The authors’ advice for staying on track: be mindful. Consciously thinking about your personal health goals before sitting down to eat may help you refrain from overindulging.