title: Body mass index gain, fast food, and physical activity: effects of shared environments over time.
abstract: OBJECTIVE
  The magnitude of environmental vs. genetic effects on BMI, diet, and physical activity (PA) is widely debated. We followed a sibling cohort (where individuals shared households in childhood and adolescence) to young adulthood (when some continued sharing households and others lived apart) to examine the role of discordant environments in adult twins' divergent trends in BMI and health behaviors and to quantify the variation in BMI and behavior among all siblings that is attributable to environmental and additive genetic effects.
  
  
  METHODS
  In the National Longitudinal Study of Adolescent Health, siblings sharing households for > or =10 years as adolescents (mean age = 16.5 +/- 1.7 years; N = 5524) were followed into adulthood (mean = 22.4 +/- 1.8 years; N = 4368), self-reporting PA, sedentary behavior, and dietary characteristics. Adult BMI and adolescent z scores were derived from measured height and weight.
  
  
  RESULTS
  Compared with those living together, twins living apart exhibited greater discordance in change in BMI, PA, and fast food intake from adolescence to adulthood. Adolescent household environments accounted for 8% to 10% of variation in adolescent fast food intake and sedentary behaviors and 50% of variation in adolescent overweight. Adolescent household effects on PA were substantially greater in young adulthood (accounting for 50% of variation) vs. adolescence. Young adult fast food intake was significantly affected by young adult household environment, accounting for 12% of variation.
  
  
  CONCLUSIONS
  These findings highlight important environmental influences on BMI, PA, and fast food intake during the transition to adulthood. Household and physical environments play an important role in establishing long-term behavior patterns.
authors.affiliation: Division of Epidemiology and Community Health, University of Minnesota, Minneapolis, USA.
authors.forename: Melissa C
authors.initials: MC
authors.lastname: Nelson
authors.forename: Penny
authors.initials: P
authors.lastname: Gordon-Larsen
authors.forename: Kari E
authors.initials: KE
authors.lastname: North
authors.forename: Linda S
authors.initials: LS
authors.lastname: Adair
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D015992:Body Mass Index; D002648:Child; D015331:Cohort Studies; D005191:Family Characteristics; D005247:Feeding Behavior / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D009043:Motor Activity / Q000502:physiology*; D009765:Obesity / Q000453:epidemiology; D035781:Siblings; D012931:Social Environment; D013223:Statistics as Topic; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D015430:Weight Gain