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

Abstract

Background: There is considerable uncertainty regarding the impact of tableware size on food consumption. Most existing studies have used small and unrepresentative samples and have not followed recommended procedures for randomised controlled trials, leading to increased risk of bias. In the first pre-registered study to date, we examined the impact on consumption of using larger versus smaller plates for self-served food. We also assessed impact on the underlying meal micro-structure, such as number of servings and eating rate, which has not previously been studied. Methods: The setting was a purpose-built naturalistic eating behaviour laboratory. A general population sample of 134 adult participants (aged 18-61 years) was randomly allocated to one of two groups varying in the size of plate used for self-serving lunch: large or small. The primary outcome was amount of food energy (kcal) consumed during a meal. Additionally, we assessed impact on meal micro-structure, and examined potential modifying effects of executive function, socioeconomic position, and sensitivity to perceptual cues. Results: There was no clear evidence of a difference in consumption between the two groups: Cohen's d = 0.07 (95% CI [− 0.27, 0.41]), with participants in the large plate group consuming on average 19.2 (95% CI [− 76.5, 115.0]) more calories (3%) compared to the small plate group (large: mean (SD) = 644.1 (265.0) kcal, versus small: 624.9 (292.3) kcal). The difference between the groups was not modified by individual characteristics. There was no evidence of impact on meal micro-structure, with the exception of more food being left on the plate when larger plates were used. Conclusions: This study suggests that previous meta-analyses of a low-quality body of evidence may have considerably overestimated the effects of plate size on consumption. However, the possibility of a clinically significant effectin either directioncannot be excluded. Well-conducted trials of tableware size in real-world field settings are now needed to determine whether changing the size of tableware has potential to contribute to efforts to reduce consumption at population-level.

Size and shape of plates and size of wine glasses and bottles: impact on self-serving of food and alcohol

“…To detect a small effect (d = 0.2) with power = 0.90, alpha = 0.05 and a conservative estimate of 0.5 for within person correlations [ 25 ], 265 participants were needed. Based on the previous plate size study [ 11 ], in which randomisation occurred immediately prior to a single study session, a dropout rate of no more than 5% was anticipated (see pre-registered protocol for more details: https://osf.io/dj3c6/ ).…”

“…We are only aware of one pre-registered study that has applied rigorous randomised controlled trial procedures to examine the effects of tableware on selection and consumption [ 11 ]. This study found no clear evidence of a statistically significant difference in either the total amount selected or consumed over a whole meal period when food was self-served on to a smaller (23 cm diameter) compared to a larger (29 cm diameter) round plate.…”

“…Due to varying effect size estimates observed in previous studies, uncertainty remains around potential effects. The aforementioned study [ 11 ] compared only two plate sizes, while previous studies have compared a wide variety of sizes. For example, in one meta-analysis, plates sizes ranged from 17 to 27.5 cm [ 6 ].…”

“…In contexts where people self-serve food and drink to then consume, consumption is dependent on, and has been shown in some studies to be near-identical in value to, selection. For example, studies demonstrate correlations of r = 0.98–0.99 between amount served and amount consumed [ 11 , 22 ] and in alcohol serving size studies most participants consume the drinks they purchase—with less than 1% waste reported (email communication with Inge Kersbergen, PhD, 2019 [ 23 ]).…”

Should an Ethical Public Servant Nudge?

“…Although outside the remit of this chapter, it is worth noting that both the interpretation and application of System 1 and System 2 thinking in designing nudges and the effectiveness of nudges has been questioned (see for example Gigerenzer 2015; Kuehnhanss 2018). The evidence for nudges using plate sizes described in the introduction, for example, is weak (Kosīte et al 2019). Thus, a focus on using nudges as a way to change behavior may take public servants attention away from other, more effective approaches.…”