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

Background: 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 more realistic portion size reductions affect energy intake. The present study investigated whether reducing the portion size of a meal by 15% affects subsequent energy intake and if this effect differs depending on whether or not consumers are aware of the portion size reduction. Methods: Participants (N = 110, female = 58) attended two test days where they were given ad libitum access to a lunch meal (main course and desserts) and a dinner meal (main course and desserts). During the first day, participants’ intake of the lunch main course was recorded and during the second day, participants were served a lunch main course either the portion size of the amount they consumed on the first day (control condition), or 15% less. Participants served 15% less were either told that the portion size was the amount they previously consumed (reduced unaware) or it had been reduced (reduced aware). Results: Compared with the first test day, participants in the second test day in both of the reduced portion size conditions consumed less energy from the lunch main course than the control condition. There were no significant effects of condition on energy intake immediately after the lunch main course or energy intake later in the day, indicating a lack of evidence for compensatory eating in response to reduced portion size. However, exploratory analyses were suggestive of participants in the reduced aware condition showing some degree of compensatory eating. Conclusion: These findings suggest that reducing meal portion size by 15% decreases meal energy intake and may not cause significant later compensatory eating. However, further research is required to understand the size of portion reductions to promote reduced daily energy intake and if this is affected by awareness of portion size reductions.