Adolescents’ Estimation of Energy Content of Standard Portion Size of Foods and Its Association with Body Mass Index

The purpose of this study is to identify the adolescents’ knowledge of the energy content of the standard portion size of foods and to investigate the association between their knowledge and energy intake and also body mass index (BMI). A total of 251 middle school adolescents participated in this study. Participants’ knowledge was assessed based on their estimation of the energy content of the standard portion size of foods. To estimate the energy intake of the subjects, 24-h recall was used. The percentage of participants who accurately estimated (that is within 20% of the true value) the energy content of the standard portion size was calculated for each of the 32 typical foods. The food for which the most participants revealed the accurate estimation was cooked rice (39.5%). The proportion of students who overestimated the energy contents was highest for vegetables (98%), and oils and sugar (90%). The female students were more likely than males to provide the accurate estimation of energy contents for standard portion size of foods. After adjusting for age and sex, the estimation level ([estimation value/true value] × 100) of the energy content of some foods had a significant positive relationship with BMI, but had no significant relationship with reported energy intake. From these results, we concluded that the knowledge of energy content of food was poor among adolescents, with some gender difference, and that their estimation of the calorie contents of foods increased along with their BMI.