title: Sex differences in genetic and environmental influences on percent body fatness and physical activity.
abstract: BACKGROUND
  Knowing the extent to which genetic and environmental factors influence percent body fatness (%Fat) and physical activity (PA) would be beneficial, since both are tightly correlated with future health outcomes. Thus, the purpose was to evaluate sex differences in genetic and environmental influences on %Fat and physical activity behavior in male and female adolescent twins.
  
  
  METHODS
  Subjects were adolescent (age range 8.3 to 16.6 yr) twins. %Fat (n = 518 twins) was assessed by bioelectrical impedance analysis (BIA) and PA (n = 296 twins) was measured using 3-Day PA Recall. Each activity was converted to total MET-minutes. Univariate twin models were used to examine sex differences in genetic and environmental factors influencing %Fat and PA.
  
  
  RESULTS
  %Fat was influenced by genetic effects in both boys and girls (88% and 90%, respectively), with slightly higher heritability estimates for girls. PA was influenced solely by environmental effects for both sexes with higher shared environmental influences in boys (66%) and higher nonshared effects in girls (67%).
  
  
  CONCLUSIONS
  When developing interventions to increase PA in adolescents, it is important to consider the environment in which it takes place as it is the primary contributor to PA levels.
authors.affiliation: Dept of Health, Exercise and Rehabilitative Sciences, Winona State University, Winona, MN.
authors.forename: Erin
authors.initials: E
authors.lastname: White
authors.forename: Jennifer D
authors.initials: JD
authors.lastname: Slane
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Klump
authors.forename: S Alexandra
authors.initials: SA
authors.lastname: Burt
authors.forename: Jim
authors.initials: J
authors.lastname: Pivarnik
mesh_terms: D000273:Adipose Tissue / Q000503:physiopathology*; D000293:Adolescent; D001823:Body Composition / Q000235:genetics / Q000502:physiology; D002648:Child; D004200:Diseases in Twins / Q000235:genetics* / Q000503:physiopathology*; D017097:Electric Impedance; D005260:Female; D059647:Gene-Environment Interaction; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000235:genetics* / Q000502:physiology*; D063766:Pediatric Obesity / Q000235:genetics* / Q000503:physiopathology*; D012727:Sex Characteristics; D012931:Social Environment; D013223:Statistics as Topic