Portion size and later food intake: Evidence on the "normalizing" effect of reducing food portion sizes

Background Historical increases in the size of commercially available food products have been linked to the emergence of a worldwide obesity crisis. Although the acute effect that portion size has on food intake is well established, the effect that exposure to smaller portion sizes has on future portion size selection has not been examined. Objective We tested whether reducing a food portion size "renormalizes" perceptions of what constitutes a normal amount of that food to eat and results in people selecting and consuming smaller portions of that food in the future. Design Across 3 experiments, participants were served a larger or smaller portion of food. In experiments 1 and 2, participants selected and consumed a portion of that food 24 h later. In experiment 3, participants reported on their preferred ideal portion size of that food after 1 wk. Results The consumption of a smaller, as opposed to a larger, portion size of a food resulted in participants believing a "normal"-sized portion was smaller (experiments 1-3, P ≤ 0.001), consuming less of that food 1 d later (experiments 1-2, P ≤ 0.003), and displaying a tendency toward choosing a smaller ideal portion of that food 1 wk later (experiment 3, P = 0.07), although the latter finding was not significant. Conclusion Because consumer preferences appear to be driven by environmental influences, reducing food portion sizes may recalibrate perceptions of what constitutes a "normal" amount of food to eat and, in doing so, decrease how much consumers choose to eat. This trial was registered at www.clinicaltrials.gov as NCT03241576.