The primary aim of this rapid review was to provide a summary of the mechanisms by which HFI is associated with child and adolescent health outcomes. The secondary aim was to identify key HFI determinants, provide an updated account of HFI-associated child/ adolescent health outcomes and build a conceptual map to illustrate and consolidate the findings.

A rapid review was performed using EMBASE, Medline, Web of Science and The Cochrane library. Inclusion criteria were observational High- income English-language studies, studies evaluating the mechanisms and associations between HFI and child health outcomes using statistical methods.

High income English-speaking countries.

Child (3-10 years) and adolescent populations (11-24 years) and their parents, if appropriate.

Eight studies reported on the mechanisms by which HFI is related to child health outcomes, suggesting that maternal mental health and parenting stress play mediating roles between HFI and child/adolescent mental health, behaviour and child weight status. Sixty studies reported on associations between HFI and various child health outcomes. HFI had significant impact on diet and mental health, which appeared to be interrelated. Sociodemographic factors were identified as determinants of HFI and moderated the relationship between HFI and child/adolescent health outcomes.

There is a gap in the evidence explaining the mechanistic role of diet quality between HFI and child weight status, as well as the interplay between diet, eating behaviours and mental health on physical child health outcomes. The conceptual map highlights opportunities for intervention and policy evaluations using complex systems approaches.