title: Does dieting make you fat? A twin study.
abstract: OBJECTIVE
  To investigate whether the paradoxical weight gain associated with dieting is better related to genetic propensity to weight gain than to the weight loss episodes themselves.
  
  
  METHODS
  Subjects included 4129 individual twins from the population-based FinnTwin16 study (90% of twins born in Finland 1975-1979). Weight and height were obtained from longitudinal surveys at 16, 17, 18 and 25 years, and number of lifetime intentional weight loss (IWL) episodes of more than 5 kg at 25 years.
  
  
  RESULTS
  IWLs predicted accelerated weight gain and risk of overweight. The odds of becoming overweight (body mass index (BMI)≥ 25 kg m(-2)) by 25 years were significantly greater in subjects with one (OR 1.8, 95% CI 1.3-2.6, and OR 2.7, 1.7-4.3 in males and females, respectively), or two or more (OR 2.0, 1.3-3.3, and OR 5.2, 3.2-8.6, in males and females, respectively), IWLs compared with subjects with no IWL. In MZ pairs discordant for IWL, co-twins with at least one IWL were 0.4 kg m(-2) (P=0.041) heavier at 25 years than their non-dieting co-twins (no differences in baseline BMIs). In DZ pairs, co-twins with IWLs gained progressively more weight than non-dieting co-twins (BMI difference 1.7 kg m(-2) at 16 years and 2.2 kg m(-2) at 25 years, P<0.001).
  
  
  CONCLUSIONS
  Our results suggest that frequent IWLs reflect susceptibility to weight gain, rendering dieters prone to future weight gain. The results from the MZ pairs discordant for IWLs suggest that dieting itself may induce a small subsequent weight gain, independent of genetic factors.
authors.affiliation: Obesity Research Unit, Department of Medicine, Division of Internal Medicine and Department of Psychiatry, Helsinki University Central Hospital, Helsinki, Finland. kirsi.pietilainen@helsinki.fi
authors.forename: K H
authors.initials: KH
authors.lastname: Pietiläinen
authors.forename: S E
authors.initials: SE
authors.lastname: Saarni
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; D001835:Body Weight / Q000235:genetics; D015331:Cohort Studies; D004032:Diet / Q000009:adverse effects* / Q000706:statistics & numerical data*; D005260:Female; D005387:Finland / Q000453:epidemiology; D005500:Follow-Up Studies; D020022:Genetic Predisposition to Disease; D006801:Humans; D033182:Intention; D008137:Longitudinal Studies; D008297:Male; D009043:Motor Activity; D009765:Obesity / Q000453:epidemiology* / Q000235:genetics / Q000523:psychology; D012907:Smoking / Q000453:epidemiology*; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires; D014430:Twins, Monozygotic; D015430:Weight Gain / Q000235:genetics; D015431:Weight Loss / Q000235:genetics