CRD summary

The review concluded that compared with non-surgical treatment of obesity, bariatric surgery led to greater body weight loss and higher remission rates of type 2 diabetes and metabolic syndrome; results were limited to two years' follow-up and were based on small numbers of studies and individuals. The conclusions reflect the evidence presented and are likely to be reliable.

Authors' objectives

To evaluate the effects of bariatric surgery compared with non-surgical treatment for obesity.

Searching

MEDLINE, EMBASE and The Cochrane Library databases were searched from inception to June 2013 with no restriction on language or publication status. Search strategies were reported in an online appendix. Trial registries of ongoing trials were examined.

Study selection

Randomised controlled trials (RCTs) that compared laparoscopic or open bariatric surgery techniques with non-surgical treatment for patients with a body mass index (BMI) of 30 or more were eligible for inclusion. Trials had to have follow-up of six months or more. Outcomes of interest were changes in body weight, body fat mass, fat-free mass, waist circumference, cardiovascular risk factors, blood lipids, quality of life or adverse events.

Bariatric surgery included laparoscopic Roux-en-Y gastric bypass, laparoscopic adjustable gastric banding, sleeve gastrectomy and biliopancreatic diversion. Control groups included alterations in dietary intake, physical activity, behavioural or lifestyle modification and pharmacotherapy. One study included adolescents (mean age range 16 to 17 years); the other studies included adults (mean age range 37 to 51 years). Zero to 88% of the participants were female. Mean baseline BMI ranged from 30 to 52. Just under half of the studies included only participants with type 2 diabetes. Three studies included only individuals who made serious attempts at weight loss. One study included patients with sleep apnoea. Studies were conducted in Australia, Italy, Denmark, China, Brazil, Taiwan and USA.

Two reviewers independently selected studies for inclusion. Disagreements were resolved by consensus.

Assessment of study quality

Study quality was assessed using criteria for sequence generation, allocation concealment and blinding (patients, healthcare providers, data collectors, outcome adjudicators and data analysts), attrition, reporting of outcomes, handling of missing data and funding. Two reviewers independently assessed study quality. Disagreements were resolved by consensus.

Data extraction

Data for relevant outcomes were extracted to enable calculation of relative risks for dichotomous data and mean differences for continuous data, together with corresponding 95% confidence intervals. For some studies the mean change from baseline to end of follow-up was calculated. Missing data were derived from other statistics, where needed. Study authors were contacted for additional data where necessary.

Two reviewers independently extracted data. Disagreements were resolved by consensus.

Methods of synthesis

Data were pooled using a random-effects model. Statistical heterogeneity was assessed using the Cochran’s Q test and the degree of inconsistency using Ι². Subgroup and sensitivity analyses were conducted. Analyses were conducted to investigate the influence of missing data on pooled effect sizes for diabetes and metabolic syndrome remission (details reported). A narrative synthesis was used where data could not be pooled in a meta-analysis. Publication bias was assessed using a funnel plot for the outcome of body weight change.

Results of the review

Eleven RCTs (796 patients, range 16 to 150) were included in the review. Follow-up ranged from 40 weeks to two years. Ten RCTs adequately conducted sequence generation. Concealment of allocation was unclear in five RCTs. None of the RCTs reported blinding of patients. Blinding of health care providers was either not reported or unclear. Three RCTs reported blinding of data collectors and outcome adjudicators and two RCTs reported blinding of data analysts. Patients in all RCTs were analysed in the groups to which they were randomised but in four studies not all individuals randomised were finally analysed. Four studies did not appropriately address missing outcome data for continuous outcomes. Missing data on diabetes remission was addressed in three of four RCTs. Missing data on metabolic syndrome remission was not addressed in three of five studies. Eight studies were free of selective reporting.

Compared with non-surgical treatment, participants who underwent bariatric surgery lost more body weight (MD -25.9kg, 95% CI -30.9 to -21; 10 RCTs), had a greater decrease in waist circumference (MD -15.6cm, 95% CI -18.1 to -13; six RCTs), had a higher remission rate for type 2 diabetes (RR 22.1, 95% CI 3.2 to 154.3; four RCTs) and a higher metabolic syndrome remission rate (RR 2.4, 95% CI 1.6 to 3.6; five RCTs). There were also reductions in triglyceride concentrations (MD -0.7mmol/L, 95% CI -1.0 to -0.4; eight RCTs) and high density lipoprotein cholesterol (MD 0.21mmol/L, 95% CI 0.1 to 0.3; eight RCTs) as a result of bariatric surgery. However, no significant differences were reported for change in total cholesterol concentration (seven RCTs) or in low density lipoprotein cholesterol (five RCTs). Statistical heterogeneity was high for outcomes of body weight (I²=95%), diabetes remission (I2=68%), triglyceride concentration (Ι²=69%), total cholesterol concentration (I²=85%), high and low density lipoprotein cholesterol concentration (I²=74% and 91%) and moderate for waist circumference (Ι²=57%) and metabolic syndrome remission (I²=49%).

There were no perioperative deaths, cardiovascular events or deaths during follow-up (11 RCTs). The most common adverse events were reoperation after bariatric surgery (8% of patients) and iron deficiency anaemia (15% after undergoing malabsorptive bariatric surgery and 2% after non-surgical treatment). Other adverse events were reported in individual studies.

Other results were reported in the paper.

Authors' conclusions

Compared with non-surgical treatment of obesity, bariatric surgery led to greater body weight loss and higher remission rates of type 2 diabetes and metabolic syndrome. However, results were limited to two years of follow-up and were based on small numbers of studies and individuals.

CRD commentary

The review question was clear with defined inclusion criteria. Some relevant sources were searched without language restrictions. Formal assessment of publication bias was conducted but with so few studies the authors did not report results as they were not likely to be reliable. Study quality was assessed and results were fully reported. Appropriate methods to reduce reviewer error and bias were used throughout the review process. Individual trial details were reported but the control treatments specific to each trial were not reported. The methods of analysis appeared appropriate. High levels of statistical heterogeneity were reported for some outcomes and the authors conducted a range of moderator analyses to explore the reasons for heterogeneity. Study sample sizes were small (few patients).

The authors’ conclusions reflect the evidence presented and are likely to be reliable.

Implications of the review for practice and research

Practice: The authors stated that the review results may not apply to individuals without prior weight loss attempts (excluded from some trials) and obese patients with multiple or severe comorbidities (excluded from most trials).

Research: The authors stated that further research was needed to evaluate evidence beyond two years of follow-up, in particular on adverse events, cardiovascular diseases and mortality.

Funding

No specific funding.

Bibliographic details

Gloy VL, Briel M, Bhatt DL, Kashyap SR, Schauer PR, Mingrone G, Bucher HC, Nordmann AJ. Bariatric surgery versus non-surgical treatment for obesity: a systematic review and meta-analysis of randomised controlled trials. BMJ 2013; 347: f5934. [PMC free article: PMC3806364] [PubMed: 24149519]

Original Paper URL

http://www.bmj.com/content/347/bmj.f5934

Indexing Status

Subject indexing assigned by NLM

MeSH

Bariatric Surgery; Body Mass Index; Humans; Obesity /complications /metabolism /therapy; Randomized Controlled Trials as Topic; Recurrence; Weight Loss

AccessionNumber

12013061328

Database entry date

01/11/2013

Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.