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Systematic review of long-term weight loss studies in obese adults: clinical significance and applicability to clinical practice

International Journal of Obesity volume 29, pages 1153–1167 (2005)Cite this article

Abstract

BACKGROUND:

Obesity is a common health problem that requires a long-term care approach. We systematically reviewed long-term (≥2 y) studies investigating dietary/lifestyle, pharmacologic, and surgical weight loss methods to assess (1) weight loss efficacy, defined by absolute weight loss and the proportion of subjects with ≥5% weight loss, (2) effects of weight loss on cardiovascular risk factors, and (3) applicability of findings from studies to everyday clinical practice.

METHODS:

The MEDLINE, HealthSTAR, and the Cochrane Controlled Trials databases were searched for studies investigating the long-term efficacy of weight loss methods in overweight and obese adults. Data were extracted for (i) weight loss after 1 y (pharmacologic studies only), 2 y, 3 y, and 4 y, (ii) proportion of subjects with ≥5% weight loss at the end of follow-up, and (iii) changes (end-of follow-up minus baseline values) in blood lipids, fasting blood glucose, and systolic and diastolic blood pressure.

RESULTS:

Dietary/lifestyle therapy provides <5 kg weight loss after 2–4 y, pharmacologic therapy provides 5–10 kg weight loss after 1–2 y, and surgical therapy provides 25–75 kg weight loss after 2–4 y. Weight loss of ≥5% baseline weight is not consistently associated with improvements in cardiovascular risk factors and these benefits appear to be intervention specific and occur mainly in people with concomitant cardiovascular risk factors. Weight loss studies have methodologic limitations that restrict the applicability of findings to unselected obese people assessed in everyday clinical practice. These limitations include an inadequate study duration, large proportions of subjects lost to follow-up, a lack of an appropriate usual care group, and a lack of reporting of outcomes in high-risk subgroups.

CONCLUSIONS:

Dietary/lifestyle and pharmacologic weight loss interventions provide modest weight loss, and may improve markers of cardiovascular risk factors although these benefits occur mainly in patients with cardiovascular risks. Studies investigating weight loss have methodologic limitations that restrict the applicability of findings to obese patients assessed in clinical practice.

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Acknowledgements

We thank Drs Arya Sharma, Hertzel Gerstein, and Anna Sawka for their helpful reviews of the manuscript.

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Authors and Affiliations

  1. Department of Medicine, McMaster University, Hamilton, Canada

    J D Douketis & C Macie

  2. Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Canada

    L Thabane

  3. Centers for Disease Control and Prevention, Atlanta, GA, USA

    D F Williamson

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  1. J D Douketis
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  2. C Macie
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  3. L Thabane
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  4. D F Williamson
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Correspondence to J D Douketis.

Appendix A1 Criteria for grading the internal validity of individual studies

Appendix A1 Criteria for grading the internal validity of individual studies

(Adapted from the Process Manual for Producing and Disseminating CTF Reviews, Canadian Task Force on Preventive Health Care (May 2002 draft), and from the United States Preventive Services Task Force Methods Manual (August 2000 draft).

Design-specific criteria and quality category definitions

Presented below are a set of minimal criteria for each study design and then a general definition of three categories: ‘good’, ‘fair’, and ‘poor’ based on those criteria. These specifications are not meant to be rigid rules, but rather are intended to be general guidelines, and individual exceptions, when explicitly explained and justified, can be made. In general,

  • a ‘good’ study is one that meets all criteria well

  • a ‘fair’ study is one that does not meet (or it is not clear that it meets) at least one criterion but has no known ‘fatal flaw’

Randomized controlled trials and cohort studies

Criteria:

  • Initial assembly of comparable groups.For randomized controlled trials (RCTs): adequate randomization, including first concealment and whether potential confounders were distributed equally among groups

  • For cohort studies: consideration of potential confounders with either restriction or measurement for adjustment in the analysis; consideration of inception cohorts

  • Maintenance of comparable groups (includes attrition, crossovers, adherence, contamination)

  • Important differential loss to follow-up or overall high loss to follow-up

  • Measurements: equal, reliable, and valid (includes masking of outcome assessment)

  • Clear definition of interventions

  • All important outcomes considered

  • Analysis: adjustment for potential confounders for cohort studies, or intention to treat analysis for RCTs.

Definition of ratings based on above criteria

Good: Meets all criteria. Comparable groups are assembled initially and maintained throughout the study (follow-up at least 80%); reliable and valid measurement instruments are used and applied equally to the groups; interventions are spelled out clearly; all important outcomes are considered; and appropriate attention to confounders in analysis. In addition, for RCTs, intention to treat analysis is used.

Fair: Studies will be graded ‘fair’ if any or all of the following problems occur, without the fatal flaws noted in the ‘poor’ category below: generally, comparable groups are assembled initially but question remains whether some (although not major) differences occurred with follow-up; measurement instruments are acceptable (although not the best) and generally applied equally; some but not all important outcomes are considered; and some but not all potential confounders are accounted for. Intention to treat analysis is carried out for RCTs.

Poor: Studies will be graded ‘poor’ if any of the following fatal flaws exists: groups assembled initially are not close to being comparable or maintained throughout the study; unreliable or invalid measurement instruments are used or not applied at all equally among groups (including not masking outcome assessment); and key confounders are given little or no attention. For RCTs, intention to treat analysis is lacking.

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Douketis, J., Macie, C., Thabane, L. et al. Systematic review of long-term weight loss studies in obese adults: clinical significance and applicability to clinical practice. Int J Obes 29, 1153–1167 (2005). https://doi.org/10.1038/sj.ijo.0802982

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  • DOI: https://doi.org/10.1038/sj.ijo.0802982

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