Korea Youth Risk Behavior Web-based Survey (KYRBWS-V) is a retrospective cohort study
that was conducted using a complex sample design, which involved stratification, clustering, and multistage sampling. This nationwide school-based survey was conducted by the Korea Centers for Disease Control and Prevention in order to evaluate the prevalence of health-risk behavior among Korean adolescent students (19
). The present study drew on the data from KYRBWS-V for students from 400 middle and 400 high schools to evaluate the association of frequency of breakfast eating with obesity, taking into account potential covariate variables such as age, frequency of smoking, frequency of drinking, the parents’ education level, economic status, frequency of vigorous physical activity (PA), frequency of moderate PA, frequency of muscular strength exercises, mental stress, and sleep duration.
For the survey, classroom teachers assigned each participating student a unique identification number, with the help of which the students could access the survey web page. On this web page, the students were first asked about their willingness to participate in the survey. Those willing were given access to a self-administered questionnaire, which they completed anonymously at the school, while those unwilling, could not proceed further. The KYRBWS-V was administered to a nationally representative group, and ethical approval was not required since it did not collect private information. This survey was valid and reliable (20
Students who were absent for long periods and students with dyslexia or dysgraphia were excluded from this study; the response rate was 97.6% (N = 75,066). The study sample comprised 72,399 students after excluding 2,667 students who did not meet the sample requirements or were absent. shows the characteristics of subjects.
The characteristics of subjects (Mean ± SD)
The adolescent students were asked to self-record their height and weight and then the BMI (kg/m2
) was calculated for each student. According to the World Health Organization (WHO) Asia-Pacific standard of obesity, people with BMIs of <23, ≥23–<25, and ≥25 kg/m2
were classified into normal, overweight, and obesity groups, respectively (22
Frequency of breakfast eating was evaluated for each adolescent student by asking one question: (Q1) “Usually, how many days did you have breakfast per week?” The available responses were  1–2 day (s),  3–5 days,  6–7 days, and  no breakfast. Then, these responses were classified into the following 4 groups: First group, 6–7 times per week (reference group); second group, 3–5 times per week; third group, 1–2 time (s) per week; and fourth group, no breakfast per week (worst condition group).
Age: the adolescents’ ages defined by the KYRBWS-V data were used without any alteration.
Frequency of smoking: This parameter was evaluated by asking the question “In the last month, how often have you smoked more than 1 cigarette per week?,” for which the response options ranged from  no to  every day.
Frequency of drinking: This parameter was evaluated by asking the question “In the last month, how often did you consume more than 1 glass of alcohol per week?,” for which the response options ranged from  no to  every day.
Parents’ education level: This parameter was evaluated by asking 2 questions, that is, “What is your mother’s education level?” and “What is your father’s education level?”; the response options ranged from  middle school or lower to  college or higher.
Economic status: This parameter was evaluated by asking the question “What is your parents’ economic status?,” for which the response options ranged from  very rich to  very poor.
Frequency of vigorous PA, such as digging, aerobics, heavy lifting, or fast cycling during the week: the response options ranged from  no to  over 5 days.
Frequency of moderate PA, such as bicycling at a regular pace, carrying light loads, or playing doubles tennis during the week: the response options ranged from  no to  over 5 days.
Frequency of muscular strength exercises, such as sit-ups, push-ups, and weight lifting or weight training, during the week: the response options ranged from  no to  over 5 days.
Mental stress: This parameter was evaluated by asking the question “What is the degree of mental stress that you experienced in the last month?,” for which the response options ranged from  very high to  none.
Sleep duration: This parameter was evaluated by asking the question “What was the daily sleep duration during the last month?,” for which the response options ranged from  ≤4 h/day to  ≥8 h/day.
All results from this study are presented in terms of mean and standard deviation. Multivariate logistic regression analyses were conducted to determine whether frequency of breakfast eating was related to overweight/obesity after adjusting for covariate variables. Statistical significance was set at P < 0.05, and all analyses were performed using SPSS Complex Sample™ version 18.0 (SPSS, Chicago, IL, USA).