Single Review on past events

Do we take into account our social environment when we decide what we eat? Yes – says psychologist Marijn Stok. In her presentation on “Eating by the norm: The influence of social norms on eating behavior” she explained why. “A person-focus alone is not enough because every individual interacts with his or her environment.” Besides physical aspects – such as the portion size that has dramatically increased in the last decades – social norms play an important role in our eating behavior. Social norms are defined as “implicit or explicit rules a social group has for the acceptable behaviors, values, and beliefs of its members”. Social norms stem from two main sources: the group’s practices and the group’s expectations. What group members themselves do (practices) are descriptive norms, whereas what group members expect others in the group to do are injunctive norms.

But why do social norms affect our behavior? – “Behavior in social influence situations is goal-driven”, says Marijn Stok, “the goal to behave accurately and the goal to build and maintain relationships.”

The aim of her PhD thesis was to determine the effects of manipulating descriptive and injunctive social norms on eating behavior. Her target population were adolescents: a population in which norms may stimulate unhealthy rather than healthy eating, in which perceived norms are even unhealthier than actual behavior, and in which correcting norm perception may stimulate healthier eating. Her research question was whether providing health-promoting peer fruit consumption norms affect adolescents’ intended and actual fruit consumption.

She conducted a first field study and could show that an injunctive norm (“A majority of high school students think other high school students should eat sufficient fruit.”) did not increase fruit consumption, whereas a descriptive norm (“A majority of high school students try to eat sufficient fruit themselves.”) did.

After having found indications that descriptive norms may be more promising in terms of improving eating behavior, she aimed to increase insight into when and in whom descriptive social norms affect eating behavior. So she conducted two further studies focusing on two potential moderators of descriptive social norm effects on eating behavior: a type of descriptive social norm (majority attitude: “73% of Dutch university students eat sufficient fruit.” vs. minority attitude: “Only 27% of Dutch university students eat sufficient fruit.”), and the identification with the norm referent group.

Compared to no-norm control conditions, descriptive norms appear to influence intended and actual fruit consumption – qualified by the extent to which the norm group is relevant. A minority descriptive norm combined with a high relevance of the norm group seems to have an especially detrimental effect.

In the next step the psychologist replicated previous findings regarding moderators and aimed to increase insight into how social norms affect eating behavior, i.e. to identify underlying mechanisms. She conducted two studies focusing on three potential mediators of descriptive social norm effects on eating behavior: self-identification, self-efficacy and attitude.

She could prove that a majority descriptive norm increased self-identification, self-efficacy and positive attitudes regarding vegetable intake behavior as compared to a minority descriptive norm. These changes in turn partially mediated the effect of the norm manipulation on participants’ behavioral intentions. This means that norm manipulations influence health behavior (intentions) in part because they affect changes in these cognitive variables.

Finally she wanted to answer another question: “Having found indications that injunctive norms may have ironic effects on eating behavior, we aimed to investigate if there are ways of communicating injunctive norms safely.” She conducted two studies focusing on the role of reactance on the effect that injunctive norms have on eating behavior: She tested a restrictive norm (“You are not allowed to ...”) and a suggested norm (“It may be better if you do not...”). The experiment showed that both types of norms were equally successful in preventing initial consumption. People who received a restrictive norm reported higher levels of psychological reactance than people who received a suggested norm. There was a negative after-effect of restrictive norms, but not of suggested norms. That means when injunctive norms must be communicated, it may be better to do so in the form of a suggestion.

Marijn Stok concluded her talk and summarized: Social norms affect eating behavior. Intervening in the social norm (perception) is a potentially viable manner to improve eating behavior. However: Their effectiveness hinges on using an appropriate social norm, stemming from a relevant referent group that is communicated in an appropriate manner to an appropriate target audience.