Background Dietary behaviors are an important factor for the childhood growth and even adulthood health of school-age children. Improving children's dietary behaviors is a pivot for promoting their nutritional status.

Objective This study investigates the dietary behaviors and their relationships with malnutrition, overweight, and obesity among school-age children in a suburb of Guangzhou, and to provide theoretical evidence for making nutrition improvement strategies targeted toward this group.

Methods A total of 1 304 students aged 9-18 years were selected from two primary schools, two middle schools, and one high school in Zengcheng District of Guangzhou in 2016 by a multi-stage stratified random sampling method according to the National Common Diseases and Health Risk Factors Surveillance project. Questionnaire surveys were conducted to collect the students' basic information (including age and gender) and selected dietary behaviors (including the intake frequencies of breakfast, fresh fruits, vegetables, diary and soy products, sugar-sweetened beverages, sweets, fried foods, and western-style fast foods in the past one week). The height and weight of students were measured. Their nutritional status such as malnutrition, overweight, and obesity were also analyzed. The constituent ratios and rates were compared by chi-square test or Fisher's exact test, and the effects of students' dietary behaviors on malnutrition, overweight, and obesity were analyzed by multinomial logistic regressions.

Results Only 43.87% and 30.90% of the students ate fresh fruits and diary & soy products every day, and 50.31% and 35.28% of the students took sugar-sweetened beverages and fried foods at least twice a week, respectively. The prevalence rates of malnutrition, overweight, and obesity were 5.21%, 12.96%, and 6.98%, respectively. The rate of obesity decreased gradually with the increase of age (χ_trend²=12.644, P < 0.001). The rate of overweight was higher in boys (14.95%) than in girls (10.39%) (P < 0.05). There was a statistical difference in the nutritional status between boys and girls in the age group of 16-18 years (P < 0.05). The prevalence rates of obesity of boys (6.25%) were higher than that of girls (0) (P < 0.05). After controlling factors such as age, sex, and parents' educational level, the multinomial logistic regression analysis results revealed that, compared to the students eating once a day or more, those taking fresh fruits once a week or less had a higher risk of malnutrition (OR=3.20, 95% CI:1.59-6.45); those taking sugar-sweetened beverages once a week or less had lower risks of overweight and obesity (OR=0.52, 95% CI:0.31-0.87; OR=0.37, 95% CI:0.19-0.71); those eating sweets once a week or less had higher risks of overweight and obesity (OR=2.73, 95% CI:1.52-4.91; OR=2.88, 95% CI:1.37-6.01); those having diary and soy products one day or less per week had a higher risk of obesity (vs. those having every day, OR=2.25, 95% CI:1.18-4.29).

Conclusion The reported dietary behaviors of school-age children in the suburb of Guangzhou are related to their nutritional status. Increasing the intake of fresh fruits may reduce the incidence of malnutrition, increasing the intake of diary and soy products may reduce the incidence of obesity, and reducing the intake of sugar-sweetened beverages may help keep a healthy weight and prevent overweight and obesity of selected students.