Can visual cues to portion size reduce the number of portions consumed? Two randomized controlled trials
Annals of Behavioral Medicine, Vol. 55, Issue 8, August 2021, pp. 746–757
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Since 1950, the portion size of many snack foods has more than doubled and obesity rates have tripled. Portion size determines energy intake, often unwittingly.
This paper tests whether salient visual cues to portion size on the packaging of high fat, sugar, or salty (HFSS) snacks can reduce consumption.
Two preregistered randomized controlled trials (N = 253 and N = 674) measured consumption in a lab and the home environment. Cues were salient, labeled stripes that demarcated single portions. Participants were randomized to cue condition or control. Consumption was measured without awareness.
The main preregistered effect of the visual cue was not statistically significant. There was some variation by subgroup. In Study 1, men were more likely to eat the whole can of potato chips than women but significantly reduced consumption when visual cues were on the pack. The effect size was large: the number of men eating more than the recommended portion fell by 33%. Study 2 monitored household consumption of chocolate biscuits (cookies) sent to family homes in gift packs. Again, the main effect was nonsignificant but there was significant subgroup variation. When the person receiving the biscuits was female, households were more likely to eat more than the recommended portion per person per day, but less likely when the visual cues were displayed. The gender of the eaters was not known. The effect size was again large: the number of households eating more than the recommended portion fell by 26%. Households with children were also less likely to open packs with visual cues compared to control packs. Both studies recorded significant increases in the likelihood of observing serving size information, together with confusion about what it means.
The studies offer some evidence that salient visual cues could play a role in tackling the high consumption of unhealthy snacks, but the effects are confined to specific subgroups and warrant further investigation.