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Open Access Research article

Weight change in control group participants in behavioural weight loss interventions: a systematic review and meta-regression study

Lauren Waters1*, Alexis St George2, Tien Chey2 and Adrian Bauman2

Author Affiliations

1 Cancer Prevention Research Centre, School of Population Health, The University of Queensland, Herston, Brisbane, QLD, 4006, Australia

2 Prevention Research Collaboration, School of Public Health, The University of Sydney, Sydney, NSW, 2006, Australia

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BMC Medical Research Methodology 2012, 12:120  doi:10.1186/1471-2288-12-120

Published: 8 August 2012



Unanticipated control group improvements have been observed in intervention trials targeting various health behaviours. This phenomenon has not been studied in the context of behavioural weight loss intervention trials. The purpose of this study is to conduct a systematic review and meta-regression of behavioural weight loss interventions to quantify control group weight change, and relate the size of this effect to specific trial and sample characteristics.


Database searches identified reports of intervention trials meeting the inclusion criteria. Data on control group weight change and possible explanatory factors were abstracted and analysed descriptively and quantitatively.


85 trials were reviewed and 72 were included in the meta-regression. While there was no change in control group weight, control groups receiving usual care lost 1 kg more than control groups that received no intervention, beyond measurement.


There are several possible explanations why control group changes occur in intervention trials targeting other behaviours, but not for weight loss. Control group participation may prevent weight gain, although more research is needed to confirm this hypothesis.