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Effects of weight loss interventions for adults who are obese on mortality, cardiovascular disease, and cancer: systematic review and meta-analysis

BMJ 2017; 359 doi: https://doi.org/10.1136/bmj.j4849 (Published 14 November 2017) Cite this as: BMJ 2017;359:j4849
  1. Chenhan Ma, foundation year 1 doctor1,
  2. Alison Avenell, professor1,
  3. Mark Bolland, associate professor2,
  4. Jemma Hudson, statistician1,
  5. Fiona Stewart, research fellow1,
  6. Clare Robertson, research fellow1,
  7. Pawana Sharma, research fellow1,
  8. Cynthia Fraser, information officer1,
  9. Graeme MacLennan, professor3
  1. 1Health Services Research Unit, University of Aberdeen, Health Sciences Building, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK
  2. 2Bone and Joint Research Group, Department of Medicine, University of Auckland, Private Bag 92 019, Auckland 1142, New Zealand
  3. 3Centre for Healthcare Randomised Trials, University of Aberdeen, Health Sciences Building, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK
  1. Correspondence to: A Avenell a.avenell{at}abdn.ac.uk
  • Accepted 4 October 2017

Abstract

Objective To assess whether weight loss interventions for adults with obesity affect all cause, cardiovascular, and cancer mortality, cardiovascular disease, cancer, and body weight.

Design Systematic review and meta-analysis of randomised controlled trials (RCTs) using random effects, estimating risk ratios, and mean differences. Heterogeneity investigated using Cochran’s Q and I2 statistics. Quality of evidence assessed by GRADE criteria.

Data sources Medline, Embase, the Cochrane Central Register of Controlled Trials, and full texts in our trials’ registry for data not evident in databases. Authors were contacted for unpublished data.

Eligibility criteria for selecting studies RCTs of dietary interventions targeting weight loss, with or without exercise advice or programmes, for adults with obesity and follow-up ≥1 year.

Results 54 RCTs with 30 206 participants were identified. All but one trial evaluated low fat, weight reducing diets. For the primary outcome, high quality evidence showed that weight loss interventions decrease all cause mortality (34 trials, 685 events; risk ratio 0.82, 95% confidence interval 0.71 to 0.95), with six fewer deaths per 1000 participants (95% confidence interval two to 10). For other primary outcomes moderate quality evidence showed an effect on cardiovascular mortality (eight trials, 134 events; risk ratio 0.93, 95% confidence interval 0.67 to 1.31), and very low quality evidence showed an effect on cancer mortality (eight trials, 34 events; risk ratio 0.58, 95% confidence interval 0.30 to 1.11). Twenty four trials (15 176 participants) reported high quality evidence on participants developing new cardiovascular events (1043 events; risk ratio 0.93, 95% confidence interval 0.83 to 1.04). Nineteen trials (6330 participants) provided very low quality evidence on participants developing new cancers (103 events; risk ratio 0.92, 95% confidence interval 0.63 to 1.36).

Conclusions Weight reducing diets, usually low in fat and saturated fat, with or without exercise advice or programmes, may reduce premature all cause mortality in adults with obesity.

Systematic review registration PROSPERO CRD42016033217.

Footnotes

  • We thank Andrew Grey for helping to resolve discrepancies in data extraction and interpretation for cardiovascular events and cancer events. We thank trialists from 16 studies for clarifying or providing additional information for this review (Andrews 2011, Aveyard 2016, Bennett 2012, de Vos 2014, Finnish Diabetes Prevention Study 2009, Goodwin 2014, Green 2015, Horie 2016, Hunt (FFIT) 2014, Katula 2013, Li (Da Qing) 2014, Logue 2005, Ma 2013, O’Neil 2016, Rejeski (CLIP) 2011, Uusitupa 1993) and others who provided information, but their trials were later found not to fulfil our inclusion criteria.

  • Contributors and sources: AA, CM, MJB, CF, and GM designed this study. CM, AA, and CF searched the literature. CM, AA, FS, CR, PS, and MJB extracted data. CM, AA, JH, MJB, and GM analysed data. CM and AA wrote the first draft of the manuscript. All authors contributed to revisions of the manuscript. AA is the guarantor.

  • Funding: The Health Services Research Unit is funded by the Chief Scientist Office of the Scottish Government Health and Social Care Directorate.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare: The Health Services Research Unit is funded by the Chief Scientist Office of the Scottish Government Health and Social Care Directorate. No author has financial relationships with any organisations that might have an interest in the submitted work in the previous three years.

  • Data sharing: All data are included in the paper or supplementary appendix. No additional data are available.

  • Transparency: AA and CM affirm that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

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