title: Predictors of initiation and persistence of unhealthy weight control behaviours in adolescents.
abstract: BACKGROUND
  Unhealthy weight control behaviours (UWCB) among adolescents have significant health and weight consequences. The current longitudinal study aimed to identify personal and socio-environmental predictors of initiation or persistence of adolescent UWCB, in order to inform development of programs aimed at both preventing and stopping UWCB.
  
  
  METHODS
  A diverse sample included 1106 boys and 1362 girls from 31 middle schools and high schools in the United States who were enrolled in Project EAT (Eating Among Teens). Project EAT explored personal, behavioural, and socio-environmental factors associated with dietary intake and body weight in adolescence. Participants completed questionnaires to assess demographics, UWCB (including several methods of food restriction, purging by vomiting or medications, smoking to control weight, or food substitutions) and personal and socio-environmental variables at two time points, five years apart, between 1998 and 2004. Logistic regression models examined personal and socio-environmental predictors of initiation and persistence of UWCB among Project EAT participants.
  
  
  RESULTS
  Results indicate that 15.5% of boys and 19.7% of girls initiated UWCB by Time 2, and 15.9% of boys and 43.3% of girls persisted with these behaviours from Time 1 to Time 2. After controlling for race/ethnicity and weight status changes between assessments, logistic regression models indicated that similar factors and patterns of factors were associated significantly with initiation and persistence of UWCB. For both boys and girls, personal factors had more predictive value than socio-environmental factors (Initiation models: for boys: R2 = 0.35 for personal vs. 0.27 for socio-environmental factors; for girls, R2 = 0.46 for personal vs. 0.26 for socio-environmental factors. Persistence models: for boys: R2 = 0.53 for personal vs. 0.33 for socio-environmental factors; for girls, R2 = 0.41 for personal vs. 0.19 for socio-environmental factors). The weight concerns model was the strongest predictor among all individual models [Initiation odds ratios (ORs) and 95% confidence interval (CI): 4.84 (3.32-7.01) for boys and 5.09 (3.55-7.30) for girls; persistence OR (CI): 4.55 (2.86-7.14) for boys and 3.45 (2.50-4.76) for girls].
  
  
  CONCLUSIONS
  In general, predictors of initiation and persistence of UWCB were similar, suggesting that universal and selective prevention programs can target similar risk factors.
authors.affiliation: Division of Epidemiology and Community Health, School of Public Health, University of Minnesota, Minneapolis, MN, USA. linde074@umn.edu.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Linde
authors.forename: Melanie M
authors.initials: MM
authors.lastname: Wall
authors.forename: Jess
authors.initials: J
authors.lastname: Haines
authors.forename: Dianne
authors.initials: D
authors.lastname: Neumark-Sztainer