Impact of reducing portion sizes in worksite cafeterias: a stepped wedge randomised controlled pilot trial

Abstract

BackgroundReducing the portion sizes of foods available in restaurants and cafeterias is one promising approach to reducing energy intake, but there is little evidence of its impact from randomised studies in field settings. This study aims to i. examine the feasibility and acceptability, and ii. estimate the impact on energy purchased, of reducing portion sizes in worksite cafeterias.MethodsNine worksites in England were recruited to reduce by at least 10% the portion sizes of foods available in their cafeterias from targeted categories (main meals, sides, desserts, cakes). In a stepped wedge randomised controlled pilot trial, each site was randomised to a date of implementation, staggered fortnightly, following a baseline period of four weeks. Impact on energy purchased was analysed using generalised linear mixed modelling. We also assessed feasibility, acceptability, and fidelity of intervention implementation.ResultsData from six of the nine randomised sites were analysed, with three sites excluded for not providing sufficient data and/or not implementing the intervention. The extent to which the intervention was implemented varied by site, with between 6 and 49% of products altered within targeted categories. Feedback following the intervention suggested it was broadly acceptable to customers and cafeteria staff. For the primary outcome of daily energy (kcal) purchased from intervention categories, there was no statistically significant change when data from all six sites were pooled: percentage change − 8.9% (95% CI: -16.7, − 0.4; p = 0.081). Each of these six sites showed reductions in energy purchased, ranging from − 15.6 to − 0.3%, which were borderline statistically significant at two sites (respective percentage changes (95% CIs): − 15.6% (− 26.7, − 2.8); − 14.0% (− 25.0, − 1.2)). Secondary outcome data are suggestive of a compensatory increase in energy purchased from food categories not targeted by the intervention, with no overall effect observed on energy purchased across all categories.ConclusionsThe results of this pilot trial suggest that reducing portion sizes could be effective in reducing energy purchased and consumed from targeted food categories, and merits investigation in a larger trial. Future studies will need to address factors that prevented optimal implementation including site dropout and application across a limited range of products.Trial Registration(ISRCTN52923504). Registered on 20th September 2016.Electronic supplementary materialThe online version of this article (10.1186/s12966-018-0705-1) contains supplementary material, which is available to authorized users.

Reductions to main meal portion sizes reduce daily energy intake regardless of perceived normality of portion size: a 5 day cross-over laboratory experiment

“…However, as is the case with any laboratory-based experiment, responses to manipulations of portion size may differ in free-living settings. The influence of portion size has also been demonstrated outside of the confines of the laboratory [11,14,[39][40][41][42], however in one free living study a reduction from a 'standard' to a 'reduced' portion size lunch was not associated with a significant reduction in overall daily energy intake [14]. The artificial environment imposed in controlled laboratorybased experiments (including but not limited to the provision of a limited number of free foods) may impact on energy intake and the extent to which compensation for reduced portion sizes occurs.…”

Factors influencing employees' eating behaviours in the office‐based workplace: A systematic review

“…Eight studies focused on eating behaviours and habits at lunchtime . Eleven studies measured eating behaviours throughout the working day and one study measured behaviours around workplace dinner time . For most studies (22 out of 23), eating behaviours were the primary outcome variable.…”

“…A number of studies covered general eating behaviours at work, and several were qualitative . Many studies measured variables related to the workplace canteen, daily energy (kcal) purchased per day, selection of lower calorie vs higher calorie food choices, fruit and vegetable consumption per customer in a canteen meal, amount of a purchased lunch meal consumed, and number of times healthy meal discount card was utilized . Some outcome variables focused on aspects of snacking, including amount of snacks consumed, type of snacks consumed, or type of snacks selected/purchased .…”

Plate size and food consumption: A pre-registered experimental study in a general population sample

“…The results of the current study also suggest that research on tableware size should not be considered an immediate research priority relative to other interventions that can be applied in similar food service settings. For example, reduction of portion sizes has a more robust evidence base from a range of settings, accompanied by evidence of underlying mechanisms [35][36][37][38][39], while reducing availability of less healthy food options is supported by preliminary evidence from real-world settings that suggests substantially larger effects [40].…”