Abstract
BackgroundSmaller portions may help to reduce energy intake. However, there may be a limit to the magnitude of the portion size reduction that can be made before consumers respond by increasing intake of other food immediately or at later meals. We tested the theoretical prediction that reductions to portion size would result in a significant reduction to daily energy intake when the resulting portion was visually perceived as ‘normal’ in size, but that a reduction resulting in a ‘smaller than normal’ portion size would cause immediate or later additional eating.MethodsOver three 5-day periods, daily energy intake was measured in a controlled laboratory study using a randomized crossover design (N = 30). The served portion size of the main meal component of lunch and dinner was manipulated in three conditions: ‘large-normal’ (747 kcal), ‘small-normal’ (543 kcal), and ‘smaller than normal’ (339 kcal). Perceived ‘normality’ of portion sizes was determined by two pilot studies. Ad libitum daily energy intake from all meals and snacks was measured.ResultsDaily energy intake in the ‘large-normal’ condition was 2543 kcals. Daily energy intake was significantly lower in the ‘small-normal’ portion size condition (mean difference − 95 kcal/d, 95% CI [− 184, − 6], p = .04); and was also significantly lower in the ‘smaller than normal’ than the ‘small-normal’ condition (mean difference − 210 kcal/d, 95% CI [− 309, − 111], p < .001). Contrary to predictions, there was no evidence that the degree of additional food consumption observed was greater when portions were reduced past the point of appearing normal in size.ConclusionsReductions to the portion size of main-meal foods resulted in significant decreases in daily energy intake. Additional food consumption did not offset this effect, even when portions were reduced to the point that they were no longer perceived as being normal in size.Trial registrationProspectively registered protocol and analysis plan: https://osf.io/natws/; retrospectively registered: https://clinicaltrials.gov/ct2/show/NCT03811210.
Highlights
Larger portions of food promote greater energy intake relative to smaller portions [1, 2]
Effect of portion size on daily energy intake Portion size condition had a significant effect on daily energy intake and there was no significant interaction between portion size condition and day
Mean daily energy intake was highest in the ‘large-normal’ condition (2543 kcals, sd = 592) and contrary to predictions, each reduction to portion size was associated with a significant reduction to daily energy intake2 (Fig. 3)
Summary
Larger portions of food promote greater energy intake relative to smaller portions [1, 2]. Participants did not fully compensate for the smaller portion sizes by eating more food, leading to an overall reduction in daily energy intake in the ‘reduced’ relative to the ‘standard’ portion size condition [10]. While each reduction resulted in a decrease in lunch intake and the reduction from ‘large’ to ‘typical’ resulted in a significant reduction in self-reported total daily energy intake, there was no significant reduction in self-reported total daily energy intake in the ‘reduced’ relative to the ‘typical’ portion size condition This suggests that participants may have responded to the reduced size lunch meal by eating more at other meals (but intake at other meals was not adjusted in response to the ‘larger’ portion size lunch). We tested the theoretical prediction that reductions to portion size would result in a significant reduction to daily energy intake when the resulting portion was visually perceived as ‘normal’ in size, but that a reduction resulting in a ‘smaller than normal’ portion size would cause immediate or later additional eating
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