Rapid Evidence Review: Implementation of Portion Size and Portion-Related Energy Reductions in Out of Home Settings

A rapid review of the published literature was undertaken to identify studies that explored portion-related interventions intended to reduce the energy selected, purchased or consumed in out-of-home settings.

Rapid reviews are based on explicit and systematic methods that can identify and extract data but have restricted scope and time frames compared to systematic reviews. The aim is to synthesise evidence quickly and provide qualitative and limited interpretation of data, in this case to inform best practice for future interventions, campaigns and frameworks, for example The Eating out Eating well framework currently being developed by Public Health Scotland and Food Standards Scotland. Whilst a rapid review will be less comprehensive, it is also more timely.

This review was conducted in accordance with the guidance developed by the Cochrane Rapid Reviews Methods Group and follows the principles for reporting reviews.

Following a published review of portion size interventions in 2015, this search was limited to papers published between 2016 and 2025 (inclusive) and was intended to identify recent empirical intervention studies. To retrieve relevant literature, the Web of Science and PubMed databases were searched using the following terms: ‘out of home’ OR restaurant OR takeaway OR ‘din* out’ OR ‘eat* out’ AND ‘portion size’. There were no restrictions on study outcomes and study population characteristics, so these were not included in the search terms. In addition, a Google search was performed to identify grey literature from relevant bodies reporting on food portion size reduction approaches. The literature search was completed in December 2025. Searches were designed to capture relevant empirical intervention studies, but review articles and other non-empirical publications identified through the search were excluded during screening.

Studies were included if they: 

1. evaluated an intervention intended to reduce the energy selected, purchased or consumed from OOH foods through portion-related mechanisms, including direct physical portion reduction, standardisation of portion sizes, redesign of meal composition, or interventions intended to increase selection of smaller portions;
2. were conducted in an OOH food environment (for example restaurants, cafés, takeaways, cafeterias/canteens) or in an experimental setting designed to reproduce an OOH portion selection or consumption context;
3. reported sufficient methodological information to interpret the study design and intervention; and
4. reported at least one relevant outcome (for example portion size selected/ordered, energy purchased/ordered, energy consumed, plate waste/leftovers, compensatory intake, acceptability or satisfaction).

Studies were excluded if they were out of scope for the review question (for example not focused on portion-size interventions), were not an empirical intervention evaluation (for example protocols, commentaries, reviews), or did not report relevant outcomes. Delphi studies and focus group-only studies were excluded because they do not provide quantitative evidence on intervention effects. Searches were limited to English-language studies published from 2016 onwards. If there was uncertainty at the stage of reviewing title and abstracts, records were retained for full-text assessment.

For each study included, the following data were extracted: 

• The study objective stated by the authors;
• The study type;
• The study design;
• An overview of the portion-related intervention approach or approaches evaluated;
• A summary of outcomes, for example, in terms of reducing calories or food waste;
• The settings in which data were collected;
• The duration of the study;
• The sample size;
• Stated limitations of the study.

Full details of the extracted data can be found in Supplementary data.