Downsizing food: A systematic review and meta-analysis examining the effect of reducing served food portion sizes on daily energy intake and body weight

Abstract

Background. Portion sizes of many foods have increased over time and reducing food portion sizes has been proposed as a public health strategy to reduce obesity. However, the extent to which reducing food portion sizes affects daily energy intake and body weight is unclear. Objective. To systematically review and meta-analyse experimental studies that have examined the effect that serving smaller vs. larger portion sizes has on total daily energy intake. Design. We used systematic review methodology to search identify eligible articles that used an experimental design to manipulate portion size served to human participants and measured energy intake for a minimum of one day. Multi-level meta-analysis was used to used to pool effects of portion size on daily energy intake. Results. Fourteen eligible studies were included and 85 effects were included in the primary meta-analysis. There was a moderate-to-large reduction in daily energy intake when comparing smaller vs. larger portions (SMD = -.709 [95% CI: -.956 to -.461], p < .001, I2 = 80.6%) and evidence of a dose dependent response. Larger reductions to portion size and reducing portion sizes of multiple meals per day both resulted in larger decreases in daily energy intake. There was also evidence of a curvilinear relationship between portion size and daily energy intake, whereby reductions to daily energy intake were markedly smaller when reducing portion size from very large portions. In a subset of studies that measured body weight (n=5), being served smaller portions was associated with less weight gain than larger portions (SMD = .536 ([95% CI: .268 to .803], p < .001, I2 = 47.0%). Conclusions. Smaller food portion sizes substantially decrease daily energy intake and there is evidence that over time this results in lower body weight. Reducing food portion sizes may be an effective population level strategy to reduce obesity.