This systematic review aims to assess the role that peer social norms play in shaping young people's food intake, focusing on the important questions of for whom and when peer social norms are related to how much young people eat. Thirty-three eligible studies were reviewed (17 correlational, 16 experimental). All but one correlational studies found significant associations between norms and food intake. All experimental studies found effects of norm manipulations on food intake, and some evidence was found of behavioural spillover effects of norms. Four moderators were distilled from our literature synthesis that stipulate for whom and when peer social norms are related to food intake: identification with the norm referent group and eating-related habit strength were found to moderate the effects of social norms on food intake; forceful injunctive norms were found not to be related to food intake; and the influence of norms seemed restricted to types of foods typically consumed in the presence of peers. The findings from this literature synthesis have important implications for research, and moderators are discussed in light of psychological theory. Where applicable, potential implications for the development of social norm-based interventions to improve young people's food intake are also highlighted.
Keywords: Social norms; adolescents; food intake; implications for interventions; systematic review; young adults.