The effect of stealth vs. declared reductions to lunch meal portion size on subsequent energy intake: A randomised control experiment.

Large reductions to meal portion size result in reduced daily energy intake due to reductions not being fully compensated for through later energy intake. However, to date no studies have investigated how relatively small portion size reductions (15 %) affect daily energy intake. The present study investigated whether reducing the portion size of a meal by 15 % affects subsequent intake and if this effect differs depending on awareness of the portion size reduction. Participants ( N = 110) attended two test days where they were given ad libitum access to a lunch meal and a dinner meal. Portion size of the lunch main course on the second test day was either the same as the amount they had consumed on the test first day (control condition), or 15 % less. Participants served 15 % less were either told that the portion size was the amount they consumed on the previous test day (reduced unaware condition) or it had been reduced (reduced aware condition). Findings revealed that lunch main course intake on the second day was lower in both of the reduced portion size conditions than the control condition. Both immediate and later subsequent intake post-lunch main course did not differ between groups, indicating a lack of evidence for compensatory eating in response to reduced portion size. However, exploratory analyses suggested that participants in the reduced aware condition showed some degree of compensatory eating. These findings suggest that reducing meal portion size by 15 % decreases meal intake and may not cause significant later compensatory eating. Trial registration: This trial was registered at www.clinicaltrials.gov as NCT06119295 • We examined the effect of a 15 % portion size reduction on subsequent energy intake. • Reducing the portion size of a lunch meal by 15 % reduced lunch meal intake. • Participants unaware of this reduction did not appear to compensate for this reduction. • Results for participants made aware of the reduction were less clear. • Reducing portion size by 15 % may not lead to compensatory intake.