Characteristics of self-selected portion size in young adults

Individuals' perceptions of portion size have not been examined with respect to body mass index (BMI; calculated as kg/m(2)), food form, food macronutrient, or food-energy density. The primary objective of this investigation was to evaluate the characteristics surrounding college students' perception of typical portions of real food items.

This study was designed as a quasi-experiment with independent repeated measures of food form (amorphous, solid, liquid), food macronutrient content (low carbohydrate, high carbohydrate, low fat, high fat), and food-energy density (low, high), as well as one independent subject variable of sex (male, female). The main dependent measure was self-selected portion size representing what each participant felt was their typical portion of 15 food/beverage items. In addition, BMI was treated as a continuous predictor variable in regressions for portion-size estimation.

Participants (n=51) chose substantially larger portion sizes as compared to reference portion sizes in 10 of the 15 food/beverage items. When accounting for intervening variables, BMI positively predicted self-selected portion size for six of 15 food/beverage items (R(2)=0.29 to 0.38). In addition, participants chose significantly larger portion sizes for high-carbohydrate foods when compared to high-fat foods (191.65 vs 145.40 g; P=0.004).

A strong relationship between BMI and large portion sizes for high-energy-density foods, snacks, and high-carbohydrate foods was found. In addition, participants selected much smaller portion sizes for high-fat foods items relative to high-carbohydrate foods.