title: Physical inactivity and obesity: a vicious circle.
abstract: OBJECTIVE
  Physical activity (PA) begins to decline in adolescence with a concomitant increase in weight. We hypothesized that a vicious circle may arise between decreasing PA and weight gain from adolescence to early adulthood.
  
  
  METHODS
  PA and self-perceived physical fitness assessed in adolescents (16-18 years of age) were used to predict the development of obesity (BMI > or =30 kg/m(2)) and abdominal obesity (waist >/=88 cm in females and > or =102 cm in males) at age 25 in 4,240 twin individuals (90% of twins born in Finland, 1975-1979). Ten 25-year-old monozygotic (MZ) twin pairs who were discordant for obesity (with a 16 kg weight difference) were then carefully evaluated for current PA (using a triaxial accelerometer), total energy expenditure (TEE, assessed by means of the doubly labeled water (DLW) method), and basal metabolic rate (BMR, assessed by indirect calorimetry).
  
  
  RESULTS
  Physical inactivity in adolescence strongly predicted the risk for obesity (odds ratio (OR) 3.9, 95% confidence interval (CI) 1.4-10.9) and abdominal obesity (4.8, 1.9-12.0) at age 25, even after adjusting for baseline and current BMI. Poor physical fitness in adolescence also increased the risk for overall obesity (5.1, 2.0-12.7) and abdominal obesity (3.2, 1.5-6.7) in adulthood. Physical inactivity was both causative and secondary to the development of obesity discordance in the MZ pairs. TEE did not differ between the MZ co-twins. PA was lower whereas BMR was higher in the obese co-twins.
  
  
  CONCLUSIONS
  Physical inactivity in adolescence strongly and independently predicts total (and especially) abdominal obesity in young adulthood, favoring the development of a self-perpetuating vicious circle of obesity and physical inactivity. Physical activity should therefore be seriously recommended for obesity prevention in the young.
authors.affiliation: Obesity Research Unit, Department of Psychiatry, Helsinki University Central Hospital, Helsinki, Finland. kirsi.pietilainen@helsinki.fi
authors.forename: Kirsi H
authors.initials: KH
authors.lastname: Pietiläinen
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kaprio
authors.forename: Patrik
authors.initials: P
authors.lastname: Borg
authors.forename: Guy
authors.initials: G
authors.lastname: Plasqui
authors.forename: Hannele
authors.initials: H
authors.lastname: Yki-Järvinen
authors.forename: Urho M
authors.initials: UM
authors.lastname: Kujala
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Rose
authors.forename: Klaas R
authors.initials: KR
authors.lastname: Westerterp
authors.forename: Aila
authors.initials: A
authors.lastname: Rissanen
mesh_terms: D000293:Adolescent; D000328:Adult; D001481:Basal Metabolism / Q000502:physiology; D001835:Body Weight / Q000502:physiology; D015331:Cohort Studies; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D006801:Humans; D008019:Life Style; D008137:Longitudinal Studies; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009765:Obesity / Q000209:etiology* / Q000235:genetics / Q000503:physiopathology*; D011237:Predictive Value of Tests; D012307:Risk Factors; D014430:Twins, Monozygotic / Q000235:genetics / Q000502:physiology