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Reducing food portion size could reduce energy intake. However, it is unclear at what point consumers respond to reductions by increasing intake of other foods. We predicted that a change in served portion size would only result in significant additional eating within the same meal if the resulting portion size was no longer visually perceived as 'normal'. Participants in two crossover experiments (Study 1: n 45; Study 2: n 37; adults, 51 % female) were served different-sized lunchtime portions on three occasions that were perceived by a previous sample of participants as 'large-normal', 'small-normal' and 'smaller than normal', respectively. Participants were able to serve themselves additional helpings of the same food (Study 1) or dessert items (Study 2). In Study 1 there was a small but significant increase in additional intake when participants were served the 'smaller than normal' compared with the 'small-normal' portion (m difference = 161 kJ, P = 0·002, d = 0·35), but there was no significant difference between the 'small-normal' and 'large-normal' conditions (m difference = 88 kJ, P = 0·08, d = 0·24). A similar pattern was observed in Study 2 (m difference = 149 kJ, P = 0·06, d = 0·18; m difference = 83 kJ, P = 0·26, d = 0·10). However, smaller portion sizes were each associated with a significant reduction in total meal intake. The findings provide preliminary evidence that reductions that result in portions appearing 'normal' in size may limit additional eating, but confirmatory research is needed. [ABSTRACT FROM AUTHOR]

Background: Smaller 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. Methods: Over 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. Results: Daily 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. Conclusions: Reductions 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 registration: Prospectively registered protocol and analysis plan: https://osf.io/natws/; retrospectively registered: https://clinicaltrials.gov/ct2/show/NCT03811210. [ABSTRACT FROM AUTHOR]

Highlights • Smaller portion sizes are associated with lower energy intake. • We test a norm range model of the portion size effect on intended intake. • A wide range of portion sizes were perceived as normal. • Portions perceived as normal did not prompt intended compensatory eating. • Portions perceived as smaller than normal prompted intended compensation. [ABSTRACT FROM AUTHOR]

External influences on eating behaviour, such as portion size, have been reliably shown to influence food intake in the laboratory. However, little research has examined whether laboratory settings under or overestimate the effect that external influences have on food intake compared to when studied in the real-world. In Study 1, 60 participants (mean age = 32 years) were randomized to consume a large (200 g) or small (100 g) portion of popcorn under controlled laboratory conditions and during a separate session in their home. Results showed that the effect of portion size on food intake was larger at home (d = 0.97) than in the laboratory (d = 0.56). Furthermore, participants reported feeling more relaxed eating at home compared to the laboratory. In Study 2, we examined whether comparable results were observed in a semi-naturalistic laboratory designed to resemble a home setting. 59 participants (mean age = 28 years) completed the same procedure as Study 1 in a standard and a semi-naturalistic laboratory setting. Although participants reported having higher levels of private self-awareness in the standard laboratory, the effect that portion size had on food intake did not differ between the standard laboratory (d = 0.50) and the semi-naturalistic laboratory (d = 0.49). The impact that external influences on eating, such as portion size, have on food intake in the real-world may be underestimated when studied under laboratory conditions. [ABSTRACT FROM AUTHOR]

Portion size impacts on the amount of energy consumed during a meal. However, research findings on participant characteristics that moderate the effect of portion size on energy intake are mixed. Using data pooled across three randomized control trials, we examined the impact of reducing meal portion size on meal energy intake in 111 adult participants varying in sex (55 M, 56 F), body weight (BMI range = 19-42) and a broad range of participant characteristics, including usual portion size, restrained, emotional and external eating, satiety responsiveness, plate clearing tendencies, concerns about wasting food and self-control. In each trial, a repeated-measures design was used and participants consumed three ad-libitum lunchtime meals differing in portion size; large-normal portion size condition (100%) vs. small-normal portion size condition (~ 75%) vs. smaller than normal portion size condition (~ 50%). In mixed ANOVAs, we did not find convincing evidence that any participant characteristic reliably moderated the impact that reducing portion size had on energy intake. For the majority of participants energy intake decreased when portion size was reduced and it was more common for participants to consistently reduce their energy intake than consume a similar amount when portion size was reduced. We also found little evidence that a sub-group of participants existed whose energy intake was consistently resistant to portion size reductions. Portion size may be a universal driver of energy intake, as reducing meal portion size appears to decrease meal energy intake among most people. Food portion downsizing may therefore be an equitable intervention approach to reducing population level energy intake. [ABSTRACT FROM AUTHOR]

Background: Eating out is now common and food served out of the home is often of low nutritional quality. Kilocalorie (kcal) labelling of food and drink products sold in restaurant chains in the US is now mandatory, although in store kcal labelling practices among major UK restaurant and takeaway chains have not been examined.Methods: During August 2018, we contacted, visited the website and/or retail outlets of major eating out and takeaway food chains in the UK, including full-service and fast-food restaurants, cafes and coffee shops, some of which had previously made a voluntary pledge to provide kcal labelling. We examined the proportion of chains providing kcal information to customers at point of choice in store and the extent to which kcal information provision adhered to labelling recommendations. We also examined the proportion of chains that did not have point of choice kcal labelling but were able to provide kcal information on request. The study protocol was pre-registered on the Open Science Framework.Results: Of the 104 eligible chains, only a small minority (18 chains, 17%) provided in store kcal labelling. Of those that did, provision of kcal information tended not to adhere to recommended labelling practices. Of the 16 eligible chains that had previously committed to a voluntary public health pledge to provide point of choice kcal labelling, labelling did not meet recommendations and 4 (25%) did not provide kcal labelling. Of the 86 chains that did not provide kcal labelling in store, kcal information was available on request from 43 (50%) chains.Conclusions: It is rare for eating out and takeaway chains in the UK to provide point of choice kcal labelling and when labelling is provided it does not adhere to recommended labelling practices. Chains that previously volunteered to provide kcal labelling as part of an industry and public health partnership do so inadequately. Voluntary policies have not resulted in adequate kcal labelling in the UK eating out of home sector. [ABSTRACT FROM AUTHOR]