Whether a person believes obesity is caused by overeating or by a lack of exercise predicts his or her actual body mass, according to new research published in Psychological Science, a journal of the Association for Psychological Science.
Obesity has become a pressing public health issue in recent years, with two-thirds of U.S. adults classified as overweight or obese and similar trends unfolding in many developed nations. Researchers Brent McFerran of the Ross School of Business at the University of Michigan and Anirban Mukhopadhyay of Hong Kong University of Science and Technology wondered whether individual beliefs might play a role in these trends.
From an initial online survey, they discovered that people seem to subscribe to one of two major beliefs about the primary cause of obesity:
"There was a clear demarcation," says McFerran. "Some people overwhelmingly implicated poor diet, and a roughly equal number implicated lack of exercise. Genetics, to our surprise, was a far distant third."
McFerran and Mukhopadhyay wanted to dig deeper to see if the pattern could be replicated and, if so, what implications it might have for behavior. They conducted a series of studies across five countries on three continents.
Data from participants in Korea, the United States, and France showed the same overall pattern: Not only did people tend to implicate diet or exercise as the leading cause of obesity, people who implicated diet as the primary cause of obesity actually had lower BMIs than those who implicated lack of exercise.
"What surprised me the most was the fact that we found lay theories to have an effect on BMI over and above other known factors, such as socio-economic status, age, education, various medical conditions, and sleep habits," says McFerran.
The researchers hypothesized that the link between people's beliefs and their BMI might have to do with how much they eat.
A study with Canadian participants revealed that participants who linked obesity to lack of exercise ate significantly more chocolates than those who linked obesity to diet. And a study with participants in Hong Kong showed that participants who were primed to think about the importance of exercise ate more chocolate than those primed to contemplate diet.
These findings provide evidence that our everyday beliefs about obesity may actually influence our eating habits—and our body mass.
According to Mukhopadhyay, this is "the first research that has drawn a link between people's beliefs and the obesity crisis, which is growing as fast as people's waistlines are."
The new findings suggest that, in order to be effective, public health campaigns may need to target people's beliefs just as much as they target their behaviors.
Explore further: Beliefs on best way to lose weight can torpedo New Year's resolutions