By guest blogger Julia Gottwald

Crisps, coke, and chocolate bars. What might be a special treat for some of us, is now a multi-billion pound industry and a staple of many people’s diets. Advertising campaigns from the snack food companies, often starring sports stars, send the message that we can offset any adverse effects of consuming their products simply by getting more physical exercise. But you can’t really “run off” a burger – recent studies show a lack of exercise is not to blame for rising obesity rates, bad diets are the real driver.

Interventions to help reduce junk food consumption are especially important for children and adolescents – prevention is better than cure in this context because obesity is so difficult to treat. Unfortunately, while health education in the classroom has shown some success among young children, adolescents have been notoriously hard to reach.

But now a large-scale study published in PNAS has tried an innovative approach to change teenagers’ attitudes towards healthy eating, and the results are promising. The researchers, led by Christopher Bryan at the University of Chicago and David Yeager at the University of Texas at Austin, argued that previous interventions have probably been unsuccessful because of a major flaw: they focused on a future, healthier you and assumed that this would be enough motivation for adolescents. In contrast, the new intervention cleverly exploits teenagers’ instinct for rebelliousness and autonomy, and the value they place on social justice.

Bryan, Yeager and their colleagues recruited over 500 teenagers (aged 13 to 14; they were the entire eighth grade at a suburban middle school in Texas) and randomly assigned some to a traditional public health appeal, others to a no-treatment control, and the remainder to receive the innovative intervention. This last group read an exposé article on the food industry. It spilled the beans about the manipulative and deceptive strategies used to make junk food more addictive and to portray the products as healthy. It also included pictures of four executives and consultants of the food industry, described as stereotypical “controlling, hypocritical adult[s]”. The hope was that these adolescents would now see choosing healthy foods as an act of autonomy and independence.

The article also explained how advertising campaigns specifically target very young and poor people, causing harm for these vulnerable groups. The researchers hoped that healthy eating could be perceived as a rebellion against social injustice.

Afterwards, the participants in this condition read a (fictitious) survey of older adolescents who wanted to “fight back against the companies by buying and eating less processed food”. Finally, these participants wrote an essay summarising why they thought people were outraged and how to rebel against the food industry – the idea was to make sure that the teenagers internalised the message.

After the exposé intervention, but not the control conditions, participants associated healthy eating with autonomy and social justice. They also rated healthy eating as being more appealing. Importantly, there were also some promising effects of the new intervention on actual behaviour. A day later the students were offered a choice of snacks and drinks in a seemingly unrelated context (announced as a reward for their hard work during the recent exam period). The teens in the exposé condition, but not the control groups, chose healthy snacks and drinks (such as fruit or water) more often over unhealthy options (like biscuits and coke). As a consequence, the exposé group consumed on average 3.6g less sugar than the controls, which corresponds to almost one teaspoon and more than 10 per cent of the daily recommended intake. Two days later, the teenagers in the exposé intervention condition were also angrier in response to sugary drink ads and less tempted to drink the sodas.

This simple classroom intervention influenced real-life choices and attitudes for at least two days whereas traditional educational approaches have struggled to have any influence at all. In this study, the researchers also did not find a significant difference between the traditional health appeal and no-treatment condition – simply educating adolescents about the effects of junk food on the body was just as (in)effective as doing nothing.

These results highlight the promise of finding new, creative approaches to reduce unhealthy eating among teenagers. But while the study shows encouraging results, it has important limitations. First, it largely relies on self-report measures. The teenagers reported on questionnaires how appealing they find healthy eating, which snacks and drinks they want, and how angry they were about soda ads. These responses might not accurately reflect their true beliefs – they may have just responded in a way they thought was expected of them. After all, the participants were cued to be angry at the food industry: they were asked to write an essay explaining why a lot of people are outraged – not being outraged did not appear to be an option.

To avoid this bias, the researchers did not disclose the real aim of the study to their participants. Rather, the intervention was disguised as an opportunity to provide feedback on a new school curriculum. Also the snack choice on day two was masked as a reward for their hard work throughout the preceding months, but it’s still possible that the teenagers may have guessed what the study was really about and the researchers did not control for this. Future studies could use more implicit measures, such as skin conductance or the Implicit Association Test, to test for subconscious attitudes. Alternatively, neuroimaging could be used to check if junk food is perceived as less rewarding in terms of brain response, which would arguably provide a more objective measure than self-report.

Also, while the effects lasted for two days, successful interventions need to be beneficial in the long-term. It is important to check if teenagers still make healthy food choices months after the experiment or if it was just a fleeting effect. And would they still be motivated by autonomy and social justice as adults? Or would we need to appeal to different values when they are older, requiring a new intervention?

Associating a healthy diet with adolescents’ own values seems to be a promising avenue to prevent obesity. But future studies will need to evaluate and develop these interventions further to ensure that teenagers make healthy choices and are not “buttered up” by the food industry.

—Harnessing adolescent values to motivate healthier eating



Post written by Julia Gottwald for the BPS Research Digest. Julia is a PhD student in the Department of Psychiatry at the University of Cambridge. Her book, Sex, Lies, & Brain Scans: How fMRI reveals what really goes on in our minds, will be released on 19 January 2017. Follow her on Twitter: @julia_gottwald.