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

Abstract

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.

Keywords: Adults; Energy density; Energy intake; Food intake; Portion control; Portion size.

Figure 1

Mean (±SEM) intakes of meals that were varied across 4 portion sizes, for trained participants (n=39), controls with overweight and obesity (n=34), and controls with normal weight: (n=29), as assessed by random coefficients models. Figure 1A: The weight of food consumed significantly increased as portions were increased (P<0.0001), and this effect did not differ across groups. Figure 1B: In trained participants, meal energy density (ED) initially decreased as portions were increased (P=0.0006), followed by an increase (P=0.001); in controls, meal ED was not affected by portion size (both P>0.35). Additionally, across all 4 portions, meal ED was significantly lower for trained participants than controls (P<0.015). Figure 1C: Meal energy intake increased as portions were increased (P<0.0001), and this effect did not differ across groups. However, across all 4 portions, trained participants had a lower energy intake than both control groups (P=0.023), whose intake did not differ.

Figure 2

Mean intake curves for the seven foods in the meal according to their taste ranking by the 88 women who completed this assessment. The curve for Rank 1 shows the mean portion size response for the food ranked as best-tasting; the highest-ranked food was different for different subjects. Subject rankings of food taste significantly influenced the trajectory of intake, according to a random coefficients analysis (P<0.0001). Foods ranked higher in taste showed a greater effect of portion size on intake. Taste rankings with different superscripts had significantly different linear coefficients for the intake curve. The scatterplots show individual food intakes and the dotted line represents consumption of the entire amount of food served (line of equality).