Objective: We tested the effect on energy intake of increasing the portion size of all foods and beverages served over 2 consecutive days.
Design: The study used a randomized crossover design.
Subjects/setting: Subjects were 32 adults from a university community.
Intervention: For 2 consecutive days in each of 3 weeks, subjects ate their main meals in a controlled setting and were given snacks for consumption between meals. We used the same two daily menus each week, but varied the portion sizes of all foods and beverages served in a given week (either 100%, 150%, or 200% of baseline amounts).
Main outcome measures: Energy intake and ratings of hunger and satiety were measured.
Statistical analyses performed: A linear mixed model with repeated measures was used.
Results: There was a significant effect of portion size on energy intake in both men and women (P<0.0001). Increasing portions by 50% increased daily energy intake by 16% (women: 335 kcal/day; men: 504 kcal/day), and increasing portions by 100% increased intake by 26% (women: 530 kcal/day; men: 812 kcal/day). Energy intake did not differ between the 2 days of each week. Daily ratings of fullness were lowest in the 100% portion condition (P=0.0004), but did not differ significantly in the 150% and 200% conditions.
Conclusions: Increasing the portion size of all foods resulted in a significant increase in energy intake that was sustained over 2 days. These data support suggestions that large portions are associated with excess energy intake that could contribute to increased body weight.