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The effect of portion size reduction on energy intake, eating enjoyment and meal satisfaction: study protocol for a randomised controlled trial comparing a standard meal with reduced portion meals with and without greater flavour intensity, food variety, and hedonic labelling

Research output: Contribution to journalArticle

Original languageEnglish
JournalBMC Public Health
DateIn preparation - 2019
DateSubmitted (current) - 4 Apr 2019


Background: Reducing portion size has been advocated as an intervention to tackle the rise in overweight and obesity. However, a reduction in portion size might promote ‘compensatory eating’ (e.g., consuming additional food later in the day) and smaller portions have been shown to reduce meal satisfaction, which might lead to low levels of adherence to any intervention. This randomised controlled trial will evaluate whether a 50% reduction in portion size at a single meal (lunch) is effective in decreasing total 24-hour energy intake (kcal). It will also explore whether small enhancements to a foodfoods comprising a meal (increased variety and flavour intensity, accompanied by a hedonic label) can increase meal enjoyment and whether these enhancements preserve meal satisfaction for a 50% smaller portion. Finally, it will explore evidence for adaptation by serving the lunch for 10-days.
Methods: 156 participants will be recruited to take part in a 12-day protocol modifying the lunch time meal for 10 consecutive week-days. Participants will be randomly allocated to one of three experimental conditions: (1) Standard condition (provided with 600-kcal lunch), (2) Nudge condition (provided with 300-kcal lunch), (3) Nudge+ condition (provided with 300-kcal ‘enhanced’ lunch – increased variety and flavour intensity, accompanied by a hedonic label). Primary outcome measures are total 24-hour energy intake (kcal), and rated meal satisfaction (mm) and meal enjoyment (mm). The secondary outcome measure is change in body weight (kg). Exploratory outcomes are measures of rated food reward (mm) and eating rate (kcal/sec ). All outcomes will be measured in the laboratory on trial days 1, 3 and 10.
Discussion: By comparing the results from the three intervention arms, this research will test whether repeated exposure to a 50% smaller portion at a single meal (lunch) is an effective approach to reduce total 24-hour energy intake. It will also evaluate whether enhancements to foods can increase meal enjoyment and meal satisfaction for a smaller portion. Our focus on reducing portion size is consistent with public health initiatives within the UK and these findings will inform our understanding of how to implement smaller portions that are accepted over the longer term.
Trial Registration: Trial retrospectively registered at under reference number ISRCTN16303598 (version 3.0, date November 15, 2017).

    Structured keywords

  • Brain and Behaviour
  • Nutrition and Behaviour


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