“That portion is too small, I’ll have something else”
: Understanding the effects of portion-size reduction on food choice

  • Roya O Shahrokni

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Research suggests that larger portion sizes promote over-consumption, and this has been linked to increased rates of obesity. Many researchers therefore suggest portion-reduction as a weight control intervention. Critically, for intake-reduction to take place, reduced-portion foods must be selected over larger competitors, yet there has been little research into the effects of portion-size reduction on food choice. Therefore, this thesis explored the effects of portion-reduction on choice, as well as methods to encourage the selection of reduced-portion foods over competitors.
The first experimental study (chapter two) found some evidence to suggest a non-linear relationship between acceptability and portion-size reduction. Based on results from this study, norm boundaries (the portion a food could be reduced to before it was considered ‘abnormally small’) and choice boundaries (the portion a preferred food could be reduced to before it was rejected for a larger competitor) were measured for multi-segment foods and compared (chapter three). It was found that participants would reject a reduced-portion of their preferred food, despite considering the portion size to be ‘normal’. Furthermore, when two foods were desired a similar amount, even a small reduction in portion size prompted the participant to reject the preferred food. Similar results regarding desire to eat and choice were found in subsequent chapters (chapters four and five). Alternatively, one experimental study (chapter four) found that participants would accept abnormally small portions of a single-segment preferred food over larger competitors, while another (chapter five) found that participants would reject a preferred ready-meal at around the same portion it was considered abnormally small.
The final two experimental chapters explored methods to encourage the selection of reduced-portion foods. Of the three experimental studies in chapter seven, two methods were found to discourage the selection of reduced-portion foods (study one, segmentation; study two, increased variety) while the final method encouraged their selection (study three, hedonic labelling). Finally, chapter eight found that products reduced by 33% in three dimensions were selected as often as standard-portions.
Outcomes from this thesis suggest that portion-reductions of commercial products when competitors are available may backfire. Specifically, consumers may instead choose larger portion products, undermining the potential benefits of portion-reduction – that being reduced intake. However, there are some steps which can be taken to reduce the likelihood of rejection, such as three-dimensional reductions and hedonic labelling.
Date of Award6 Dec 2022
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorDanielle Ferriday (Supervisor) & Jeff Brunstrom (Supervisor)

Keywords

  • portion size
  • psychology
  • obesity
  • food choice

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