Comparing the portion size effect in women with and without extended training in portion control: A follow-up to the Portion-Control Strategies Trial

Following a 1-year randomized controlled trial that tested how weight loss was influenced by different targeted strategies for managing food portions, we evaluated whether the effect of portion size on intake in a controlled setting was attenuated in trained participants compared to untrained controls. Subjects were 3 groups of women: 39 participants with overweight and obesity from the Portion-Control Strategies Trial, 34 controls with overweight and obesity, and 29 controls with normal weight. In a crossover design, on 4 different occasions subjects were served a meal consisting of 7 foods that differed in energy density (ED). Across the meals, all foods were varied in portion size (100%, 125%, 150%, or 175% of baseline). The results showed that serving larger portions increased the weight and energy of food consumed at the meal (P < .0001), and this effect did not differ across groups. Increasing portions by 75% increased food intake by a mean (±SEM) of 111 ± 10 g (27%) and increased energy intake by 126 ± 14 kcal (25%). Across all meals, however, trained participants had lower energy intake (506 ± 15 vs. 601 ± 12 kcal, P = .006) and lower meal ED (1.09 ± 0.02 vs. 1.27 ± 0.02 kcal/g; P = .003) than controls, whose intake did not differ by weight status. The lower energy intake of trained participants was attributable to consuming meals with a greater proportion of lower-ED foods than controls. These results further demonstrate the robust nature of the portion size effect and reinforce that reducing meal ED is an effective way to moderate energy intake in the presence of large portions.