Public health communications are designed to tackle significant medical issues such as obesity, AIDS, and cancer. For example, what message can best combat the growing obesity epidemic? Are educational messages effective at increasing condom use? Should cancer prevention messages stress the health risks of too much sun exposure? These are not just medical problems. These are fundamentally questions about perception, beliefs, and behavior. Psychologists bring a unique expertise to these questions and are finding consequential, and often non-intuitive, answers.

In our own recent research, we investigated the psychological repercussions of the American Medical Association’s decision to label obesity a disease. As our waistlines continue to expand—approximately 35% of Americans are categorized as obese compared to just 15% of Americans a mere 30 years ago—it is not surprising that the AMA sought to change the way we approach this complex issue by declaring obesity a disease. With this decision, the medical profession hoped to highlight the dire consequences of the growing epidemic and to elicit more resources for research and treatment. However, as psychologists, we wanted to understand how the “obesity is a disease” message changes the behavior of the people the AMA is trying to help.

To examine the psychological consequences, we first randomly assigned over 700 participants, across three studies, to read either an article describing the decision of the AMA to label obesity a disease or to a control condition article. The control article either argued that obesity should not be a disease or stressed the importance of eating less and exercising more. After reading the assigned article, participants answered questions about their attitudes regarding weight and health. We found that obese individuals in the disease, relative to the control condition, reported less concern about their weight and placed less importance on dieting for health reasons. And, importantly their reduced concern for weight led to higher calorie food choices.

Next, we sought to explore the reasons for these different attitudes and food choices. Disease is a term suggesting that our bodies are not functioning optimally. Thus, we expected this message to promote the perception that weight is unchangeable. Indeed, as physicians debated the pros and cons of the AMA’s decision, some noted that an unintended consequence might be that patients would now view obesity as something they have no control over. Using the same methods reported above, we ran two additional studies, this time assessing beliefs about the controllability of weight and examining motivational costs of these changes in beliefs. Across two studies, participants given the “obesity is a disease” argument reported a stronger belief in the fixed, unchangeable nature of weight. And, this had motivational costs, including reduced value placed on weight-related goals.

Psychological research on the unanticipated effects of public health messages goes beyond the obesity epidemic. For example, critics of behavioral interventions aimed at reducing teen pregnancy and HIV argue that educational messages about condoms encourage adolescent sexual behavior. However, the opposite occurs. The interventions not only reduce the frequency of sex but also decrease the number of sexual partners while also encouraging greater condom use. Another example involves messages designed to promote sunscreen use. At first glance, it may seem irrelevant whether this message tells people, “using sunscreen decreases your risk of cancer” or whether it says, “not using sunscreen increases your risk of developing cancer.” However, this difference is meaningful for motivating healthy behavior: the first message is gain-based and is more effective at encouraging prevention behaviors, such as using sunscreen. The latter message is loss-based framing and is more effective at promoting detection behaviors such as cancer screenings.

Understanding public health labels and messages is not a matter of intuition. And, when such vital issues as obesity, AIDS and cancer are on the table scientific evidence is critical. To best tackle these public health issues, we need the data — all available data — to inform that quest. This includes the “harder” medical science as well as the “softer” psychological or social side. As health care concerns and costs mount in the United States, the importance of integrating psychology with public health research is increasingly germane. Yet, many people are not aware of the critical role the social sciences can play in promoting a healthier society. This is evidenced in the U.S. House of Representatives’ recent debates over bills to dramatically cut social science research funding. It is becoming more and more clear that social scientists have an obligation to better explain why and how our sciences contribute to questions of national importance.

Are you a scientist who specializes in neuroscience, cognitive science, or psychology? And have you read a recent peer-reviewed paper that you would like to write about? Please send suggestions to Mind Matters editor Gareth Cook, a Pulitzer prize-winning journalist and regular contributor to NewYorker.com. Gareth is also the series editor of Best American Infographics, and can be reached at garethideas AT gmail dot com or Twitter @garethideas.