The high availability of energy-dense nutrient-poor discretionary foods in large serving and package sizes may have shifted portion size norms (described as a typical perception of how much people choose to eat from a given food at a single eating occasion) towards larger sizes. Few public health recommendations exist around appropriate discretionary food portion sizes. This qualitative study aimed to explore the underlying rationale of portion size norms of discretionary foods among Australian adults 18–65 years.

Four focus group sessions were conducted. Collected data were analysed using inductive thematic analysis.

Focus groups were held online via Zoom between September and October 2023.

Thirty-four participants were recruited in the study (mean age 38 years, 19 females).

The key themes raised from inductive analysis were personal factors, eating context factors and food environment factors relevant to the portion size norms. A framework was established to illustrate the interaction across these themes during the conceptualisation of the norms. For serving size availability, consumers found that there were limited serving size choices when making portion size selections and lacked the knowledge and skills in portion control.

These findings highlight the need to make positive changes to the current food environment and develop relevant public health guidelines around appropriate portion sizes to promote healthier portion size norms and enable better portion control.