Two-year controlled effectiveness trial of a school-based intervention to prevent obesity in Chilean children

Objective: Obesity prevalence among Chilean children is 19.4%. The present study aimed to assess the effectiveness of a school-based obesity prevention programme. Design: Non-randomized controlled study. The intervention included activities in nutrition and physical activity, fully applied the first year and partially in the second one. Primary outcomes were BMI 7 score (BMIZ) and obesity prevalence; secondary outcomes were waist circumference and triceps skinfold thickness. Time effects were assessed by changes in BMI-related variables by gender and period (ANOVA and Turkey test), while intervention effects were determined by comparing changes in G) obesity prevalence by gender and period (PROC GENMOD) and (ii) BMIZ according gender, age and period (PROC MIXED). Setting: Primary schools in the Chilean cities of Casablanca (intervention group) and Quillota (control group). Subjects: one thousand seven hundred and fifty-nine children from three schools (intervention group) and 671 from one school (control group). Results: Over the two years, obesity prevalence and BMIZ declined significantly in the intervention group; from 17.0% to 12.3% and 14.1% to 10.3% in boys and girls, respectively, and from 0.62 to 0.53 and 0.64 to 0.58, respectively. In the control group, obesity remained stable at about 21% and 15%, while BMIZ increased significantly in the second year. BMIZ declined in both genders and all age categories in the intervention group during the first year (significant only in younger boys). No changes occurred during the Summer, while during the second year, BMIZ increased in boys and girls from both groups (significant only in the younger control boys). Obesity declined significantly only in boys during the first year. Conclusion: Effectiveness was greater in the first school year and more evident in younger boys.