A systematic review of the relationship between portion size and children’s body weight and BMI

Research suggests food portion size (PS) contributes to total energy intake, with larger PS increasing energy intake, and thereby potentially increasing risk of overweight and obesity. However, it remains unclear whether long-term increases in PS are sufficient to substantially affect body weight. This systematic review assessed the independent effect of PS (food/meal/snack size in grams) on indexes of body weight (e.g., BMI percentile, BMI z-scores) in children from birth to 19 years. 1,367 articles (duplicates removed) published until 2021 were identified using six electronic databases: PsycINFO, MEDLINE, EMBASE, Web of Science, Cochrane Library and ProQuest Dissertations & Theses Global. Articles were screened independently by two researchers; 20 studies were included (two interventions, one longitudinal and 17 cross-sectional). A narrative review was conducted due to high levels of heterogeneity. Some studies (n = 17) reported positive associations between PS and body weight or BMI, but results were restricted by participant sex and food type. Overall, there was no compelling evidence of a causal relationship. One key difference between studies was the measurement of PS (e.g., food diaries, online PS task). Accordingly, it was not possible to determine whether PS independently contributes to body weight or BMI, or whether children with higher body weight or BMI consume larger PS. Critically, this review highlights the need for consistency in the measurement of PS, as well as for more prospective research to determine whether there is a causal relationship between PS and indexes of body weight in children.