Objective: A previous study showed that increasing the portion sizes of all foods led to an increase in energy intake that was sustained over 2 days. The objective of the present study was to determine whether participants would compensate for excess energy intake or continue to overeat when portion sizes were increased for 11 days.
Research methods and procedures: Participants in the study were 23 normal-weight and overweight participants (10 women and 13 men). All of their foods and caloric beverages were provided during two different periods of 11 consecutive days, which were separated by a 2-week interval. During one period, standard portions of all items were served; during the other, all portion sizes were increased by 50%.
Results: The 50% increase in portion sizes resulted in a mean increase in daily energy intake of 423 +/- 27 kcal (p < 0.0001), which did not differ significantly between women and men. This increase was sustained for 11 days and did not decline significantly over time, leading to a mean cumulative increase in intake of 4636 +/- 532 kcal. A significant effect of portion size on intake was seen at all meals and in all categories of foods except fruit (as a snack) and vegetables. The effect of portion size on intake was not influenced by the body weight status of participants.
Discussion: These results strengthen the evidence suggesting that increased portions contribute to the overconsumption of energy and to excess body weight.