Discussion
In two experiments we examined the impact of reducing food portion size on energy intake and found that when served smaller portions participants consumed less energy across the course of a day. Importantly, there was no evidence of moderation by SEP (defined in Study 1 as highest educational qualification achieved and in Study 2 as subjective social status). The effect portion size had on energy intake was similar in participants from higher vs. lower SEP and findings were consistent across a range of SEP measurements, including education level, household income, childhood and self-perceived (subjective SEP).Our findings are consistent with a large body of evidence showing that smaller portions decrease energy intake [In the present studies there was no evidence that energy intake from non-manipulated study foods (e.g., consuming more later in the day after receiving larger vs. smaller portions) differed by SEP. This suggests that individuals with lower SEP (defined using highest educational qualification achieved (Study 1) and subjective social status (Study 2) are no more susceptible to eating beyond energy needs after being served large meals than those with higher SEP, contrary to recent suggestions [It has been suggested that reducing portion sizes of commercially available food could be an effective strategy to promote population health [There are several strengths and limitations to note. Findings were replicated across two studies, regardless of how SEP was measured, and were robust to a range of sensitivity analyses. We recruited a diverse sample in terms of SEP and this provided a strong test of the hypothesis that SEP moderates the influence of portion size on energy intake. The sample was predominantly white and although this is consistent with population demographics in the UK, our findings may not generalise to other ethnic groups. Importantly we only recruited females across both studies which may limit generalisability. However, given evidence that sex does not moderate the portion size effect [