title: Inaccuracies in food and physical activity diaries of obese subjects: complementary evidence from doubly labeled water and co-twin assessments.
abstract: OBJECTIVE
  To study whether eating or physical-activity (PA) habits differ between obese and non-obese monozygotic (MZ) co-twins independent of genetic effects.
  
  
  METHODS
  Rare MZ pairs discordant for obesity (n=14, body mass index difference 5.2+/-1.8 kg m(-2)) and weight-concordant control pairs (n=10, 1.0+/-0.7 kg m(-2)), identified through a population-based registry of 24-28-year-old twins (n=658 MZ pairs), completed 3-day food and PA diaries and eating behavior questionnaires. Each twin was asked to compare his/her own eating and PA patterns with the co-twin's behavior by structured questionnaires. Accuracy of energy intake was validated by doubly labeled water.
  
  
  RESULTS
  Non-obese co-twins consistently reported that their obese twin siblings ate more food overall, consumed less healthy foods and exercised less than the non-obese co-twins do. However, no differences in energy intake (9.6+/-1.0 MJ per day vs 9.8+/-1.1 MJ per day, respectively) in the food diaries or in the mean PA level (1.74+/-0.02 vs 1.79+/-0.04, respectively) in the PA diaries were found between obese and non-obese co-twins. A considerable underreporting of energy intake (3.2+/-1.1 MJ per day, P=0.036) and overreporting of PA (1.8+/-0.8 MJ per day, P=0.049) was observed in the obese, but not in the non-obese co-twins.
  
  
  CONCLUSIONS
  On the basis of rare MZ twin pairs discordant for obesity, the co-twin assessments confirmed substantial differences in eating and PA behavior between obese and non-obese persons. These may be overlooked in population studies using food and PA diaries because of considerable misreporting by the obese.
authors.affiliation: Department of Psychiatry, Obesity Research Unit, Helsinki University Central Hospital, Helsinki, Finland. kirsi.pietilainen@helsinki.fi
authors.forename: K H
authors.initials: KH
authors.lastname: Pietiläinen
authors.forename: M
authors.initials: M
authors.lastname: Korkeila
authors.forename: L H
authors.initials: LH
authors.lastname: Bogl
authors.forename: K R
authors.initials: KR
authors.lastname: Westerterp
authors.forename: H
authors.initials: H
authors.lastname: Yki-Järvinen
authors.forename: J
authors.initials: J
authors.lastname: Kaprio
authors.forename: A
authors.initials: A
authors.lastname: Rissanen
mesh_terms: D000328:Adult; D015992:Body Mass Index; D015930:Diet Records; D002149:Energy Intake; D004734:Energy Metabolism; D015444:Exercise; D005247:Feeding Behavior / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D009765:Obesity / Q000453:epidemiology / Q000523:psychology*; D011996:Records / Q000592:standards*; D014342:Truth Disclosure; D014430:Twins, Monozygotic / Q000523:psychology*; D055815:Young Adult