Original Article

International Journal of Obesity (2012) 36, 456–464; doi:10.1038/ijo.2011.160; published online 9 August 2011

Does dieting make you fat? A twin study

K H Pietiläinen1,2,3, S E Saarni2,4, J Kaprio2,3,4 and A Rissanen1

  1. 1Obesity Research Unit, Department of Medicine, Division of Internal Medicine and Department of Psychiatry, Helsinki University Central Hospital, Helsinki, Finland
  2. 2Finnish Twin Cohort Study, Department of Public Health, Hjelt Institute, University of Helsinki, Helsinki, Finland
  3. 3Institute for Molecular Medicine, Helsinki, Finland
  4. 4Department of Mental Health and Substance Abuse Services, National Institute for Health and Welfare, Helsinki, Finland

Correspondence: Dr KH Pietiläinen, Department of Medicine, Division of Internal Medicine and Department of Psychiatry, Obesity Research Unit, Biomedicum Helsinki, Helsinki University Central Hospital, PO Box 700, Helsinki 00029, Finland. E-mail: kirsi.pietilainen@helsinki.fi

Received 17 December 2010; Revised 16 May 2011; Accepted 24 June 2011
Advance online publication 9 August 2011





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.



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 5kg at 25 years.



IWLs predicted accelerated weight gain and risk of overweight. The odds of becoming overweight (body mass index (BMI)greater than or equal to25kgm−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 0.4kgm−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 1.7kgm−2 at 16 years and 2.2kgm−2 at 25 years, P<0.001).



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.


weight loss; weight regain; longitudinal studies; genetic; twins

Extra navigation