Effect of secular trends on a primary prevention trial: The HEALTHY study experience

Background: From baseline to end of study (2006-C2009), the percentage of students with a body mass index (BMI) ≥85^th percentile decreased by over 4% in both intervention and control middle schools participating in the HeALtHy study, despite intervention schools delivering an intense program of behavioral and environmental change aimed at reducing diabetes risk. Here we describe secular trends and environmental changes that might explain the similar decrease in bMi. Methods: Data were collected annually in 21 control and 21 intervention schools to document the status of the school food service and physical education (Pe) environments, including a study-developed survey to document trends, changes, and activities. student data were collected to determine changes in behaviors that would affect bMi. Results: both intervention and control schools were equivalent across the 3 years of the study in terms of administrative function, operation, trends, changes, and activities affecting total school food and physical education environments. in intervention schools, students spent 6% more Pe class time in moderate-to-vigorous physical activity. Control and intervention schools had equivalent elimination of vending machines, but intervention schools made more changes in the nutritional quality of food offered. Conclusions: both control and intervention schools experienced similar secular trends in school policies and mandates addressing childhood obesity. schools and students may have been influenced by being in a large, national study with the goal to reduce risk factors for diabetes. Combined with increasing public awareness of the childhood obesity epidemic, these factors likely minimized differences in effects on the percentage with BMI ≥85 ^th percentile.