RESUMO
BACKGROUND: Increases in portion size are thought by many to promote obesity in children. However, this relationship remains unclear. Here, we explore the extent to which a child's BMI is predicted both by parental beliefs about their child's ideal and maximum portion size and/or by the child's own beliefs. METHODS: Parent-child (5-11 years) dyads (N = 217) were recruited from a randomized controlled trial (n = 69) and an interactive science centre (n = 148). For a range of main meals, parents estimated their child's 'ideal' and 'maximum tolerated' portions. Children completed the same tasks. RESULTS: An association was found between parents' beliefs about their child's ideal (ß = .34, p < .001) and maximum tolerated (ß = .30, p < .001) portions, and their child's BMI. By contrast, children's self-reported ideal (ß = .02, p = .718) and maximum tolerated (ß = -.09, p = .214) portions did not predict their BMI. With increasing child BMI, parents' estimations aligned more closely with their child's own selected portions. CONCLUSIONS: Our findings suggest that when a parent selects a smaller portion for their child than their child self-selects, then the child is less likely to be obese. Therefore, public health measures to prevent obesity might include instructions to parents on appropriate portions for young children.