The influence dishware size has on meal energy intake is unclear and no study to date has examined the impact on total daily energy intake. In a pre-registered RCT we investigate the impact of breakfast dishware size on breakfast and post-breakfast energy intake, as well as daily energy intake and hunger/fullness. In a repeated-measures design, 50 females (aged 18-77 years) were randomised to receive smaller or larger breakfast dishware on two separate days. Energy intake was also measured during the rest of the day. The primary outcomes were breakfast and post-breakfast energy intake (kcal). Secondary outcomes were total daily energy intake (kcal), and hunger/fullness (rated from 0 to 100). We examined if results differed by socioeconomic position (SEP). Dishware did not affect energy intake at breakfast (smaller: M = 394.8 kcal; SD = 172.2 larger: M = 394.4 kcal; SD = 164.4; d = 0.003, p = 0.98), and there was no statistically significant evidence that dishware size affected energy intake after breakfast, though post-breakfast energy intake was somewhat higher after using larger breakfast dishware (smaller: M = 1974.6 kcal; SD = 475.2; larger: M = 2077.5 kcal; SD = 525.9; d = -0.27, p = 0.06). Total daily energy intake, hunger and fullness ratings did not significantly differ between dishware conditions. There was no evidence that SEP moderated the effect of dishware size on energy intake. Smaller vs. larger breakfast dishware size had no significant effect on breakfast or post-breakfast energy intake, hunger, fullness, or daily energy intake. Previous studies may have overestimated the promise of dishware size as an intervention for reducing energy intake. Alternative interventions targeting the food environment should now be prioritised.
Keywords: Bowl size; Dishware size; Food environment; Nudging; Plate size; Portion control; Tableware.
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