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

This rapid scoping review summarises recent evidence on portion-related interventions in out of home (OOH) settings that aim to reduce the energy selected, purchased or consumed from meals, snacks or drinks. The review includes evidence published from 2016 onwards and considers intervention type, study setting, outcomes measured, and implications for policy and implementation in Scotland.

The evidence suggests that portion-related interventions can reduce energy purchased or consumed in OOH settings, particularly when they change the default offer, standardise smaller portions, or redesign meals so that lower-energy choices are easy and acceptable. Direct physical portion reduction and portion standardisation were the most commonly identified intervention components. Smaller portions were generally more acceptable when they were clearly offered, framed as a normal option, and accompanied by proportionate price reductions.

Portion composition and meal redesign may also reduce energy while preserving perceived meal size or value. These approaches include reducing higher-energy meal components, increasing lower-energy components, or combining modest portion reductions with changes to meal composition. Such approaches may be especially relevant where visible portion reduction could affect perceived value for money or customer acceptability.

Evidence for information and labelling approaches was more mixed. Information alone had limited and context-dependent effects but appeared more useful when paired with changes to the ordering environment, pricing, defaults or menu architecture. Across studies, portion choice was shaped not only by preference, but also by cues about value, normality, availability and convenience.

The evidence base has important limitations. Studies varied in setting, intervention type, outcome measure and follow-up duration. Many were laboratory or simulated ordering studies, while fewer assessed longer-term implementation in real-world OOH businesses. Few studies measured compensatory behaviour, such as additional side orders, later intake, or snacking after a reduced portion. Evidence on business outcomes, including sales, customer satisfaction, operational burden and commercial feasibility, remains limited.

For Scotland, the current evidence is most immediately useful for guidance, piloting and voluntary implementation rather than immediate mandatory policy. Promising approaches include making smaller portions more visible, using smaller portions as defaults, aligning prices with portion size, and redesigning meals to reduce energy while maintaining perceived value. Future Scottish evaluations should measure total energy purchased per transaction, compensation, customer acceptability, food waste, sales patterns and business implementation costs.

Foods consumed out of home (OOH) include sit-down meals purchased from restaurants, pubs and bars, café and coffee shops, workplaces, takeaways, and food purchased for immediate consumption on the go such as sandwiches or baked goods from convenience stores, bakeries and sandwich shops, vending machines and more. OOH foods and drinks can contribute meaningfully to daily energy intake and are often high in nutrients of public health concern, including saturated fat, free sugars and sodium. 

OOH foods also come in a wide range of portion sizes. A central rationale for reducing portion sizes is the “portion size effect”: people tend to consume more when offered larger portions, package sizes, or tableware, even without reporting greater hunger. Reducing how much is offered, for example through smaller portion sizes, smaller default sizes, or smaller individual unit sizes or packages, can reduce the risk of overconsumption of energy and therefore contribute to reducing the risk of weight gain in OOH settings.

Reducing portion sizes could also have implications for businesses. In principle, smaller portions can reduce ingredient costs and, in some contexts, food waste, although impacts on revenue and acceptability depend on pricing, promotions, and how changes are implemented. In addition to directly reducing the standard portion sizes, reduction in energy can be achieved using several methods, including reducing the availability of large portions, increasing availability of smaller portions, advertising smaller portions, restricting promotions of large portion sizes and using smaller table- or serve-ware.

This rapid scoping review summarises recent evidence on portion-related interventions in OOH settings that aim to reduce the energy selected, purchased or consumed from meals, snacks or drinks. These interventions include direct reductions in physical portion size, standardisation of portion sizes, redesign of meal components to lower the energy content of the portion offered, and behavioural or informational approaches intended to support selection of smaller portions. Only evidence after 2016 was included because earlier evidence was included in a review of consumer-side portion size interventions. A rapid review method is used, consistent with prior FSS rapid reviews. 

To summarise recent evidence on portion-related interventions in OOH contexts that aim to reduce the energy selected, purchased or consumed, with emphasis on intervention type, study setting, outcomes, and implications for policy and implementation in Scotland.

3.1 Research questions

1. What portion-related approaches to reducing the energy selected, purchased or consumed in OOH settings have been evaluated since 2016, including direct physical portion reduction, portion standardisation, meal-component redesign, and interventions that support selection of smaller portions?
2. What outcomes have been measured (for example, energy purchased, energy consumed, compensatory intake, food waste), and what direction of effects is observed?
3. What do we know about feasibility and implementation considerations relevant to the Scottish OOH context?