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The Cochrane Database of Systematic Reviews logoLink to The Cochrane Database of Systematic Reviews
. 2018 Sep 6;2018(9):CD013119. doi: 10.1002/14651858.CD013119

Interventions for weight loss in people with chronic kidney disease who are overweight or obese

Marguerite M Conley 1,✉, Catherine M McFarlane 2, Helen L MacLaughlin 3, David W Johnson 4, Katrina L Campbell 5
PMCID: PMC6513610

Abstract

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

To assess the efficacy of weight reduction interventions in overweight and obese adults with CKD; including those with ESKD being treated with dialysis, kidney transplantation, or conservative management.

Background

Description of the condition

Obesity and chronic kidney disease (CKD) are highly prevalent worldwide and result in substantial healthcare burdens. Overweight and obesity are defined as ''abnormal or excessive fat accumulation that presents a risk to health'' and are commonly defined by a measure of body mass index (BMI) (WHO 2017). A BMI of > 25 kg/m2 is considered overweight and a BMI > 30 kg/m2 is considered obese. Since 1980, worldwide obesity has almost doubled and approximately 39% of adults are now overweight and 13% are obese (WHO 2017). In 2015, an increased BMI accounted for around 4 million deaths and 120 million disability‐adjusted life years (DALYs) worldwide (Afshin 2017).

CKD is defined as “kidney damage for ≥3 months, as defined by structural or functional abnormalities of the kidney, with or without decreased GFR or GFR <60 mL/min/1.73m2 for ≥3 months, with or without kidney damage” (KDIGO 2013). CKD is categorised into five stages, with the fifth stage, end‐stage kidney disease (ESKD) requiring renal replacement therapy (RRT) for survival (KDIGO 2013). An estimated 11% to 13% of adults worldwide have CKD with the prevalence steadily increasing (Hill 2016). All stages of CKD have an increased risk of cardiovascular disease (CVD), increased death and poorer quality of life (van der Velde 2011; Weiner 2004). Global death rates for CKD rose by 41% between the years 1990 to 2016 (GBD 2016) and CKD is now the 13th leading male and 11th leading female risk of DALYs (GBD 2017) and accounts for 25% of all BMI‐related DALYs (Afshin 2017).

Obesity is considered a strong predictor of new onset of CKD and progression to ESKD (Kovesdy 2017; Tsujimoto 2014). In the general population, compared to those of a healthy weight (BMI of 20 to 25 kg/m2), obese adults with a BMI ≤ 35 kg/m2 are at a 122% increased risk of developing of ESKD (Herrington 2017). Obesity increases the risk of developing diabetes and hypertension, which are the two leading causes of CKD. Furthermore, in obese individuals, a compensatory hyperfiltration occurs to meet the increased metabolic demands of the higher body weight (Darouich 2011). The ensuing increase in intraglomerular pressure can damage the kidneys and raise the risk of developing CKD in the long term. For those who reach ESKD, obesity adversely affects eligibility for kidney transplantation (Ladhani 2017), with morbidly obese patients 44% less likely to receive a donor kidney (Segev 2008).

A recent systematic review explored the association between obesity and cardiovascular morbidity and death in CKD (Ladhani 2017), highlighted that obesity (defined by BMI) may be protective for death (all causes) in the predialysis and haemodialysis (HD) populations, but not in peritoneal dialysis (PD) or transplant recipients. This relationship however is unlikely to be linear, with the highest risk of death occurring at extreme BMI categories. The biological rationale for the obesity paradox across different CKD stages remains unclear. It is proposed that obesity may lead to improved stem cell mobilisation, better bone strength, improved haemodynamic tolerance, and preserved energy stores (Stenvinkel 2008). However the relationship remains complex and is likely confounded by a number of factors including muscle mass, life expectancy, co‐morbidities, nutritional status and measurement of obesity (Ladhani 2017; Stenvinkel 2008). These conflicting data demonstrate gaps in our current understanding of the links between obesity, kidney disease and clinical outcomes. Accordingly, this places emphasis on evaluating the safety and efficacy of weight loss interventions in obese or overweight patients with CKD (of various stages).

Description of the intervention

This review will focus on interventions designed to promote intentional weight loss to improve patient outcomes. Weight loss interventions are typically aimed towards reducing an individual’s energy intake and/or increasing daily energy expenditure in order to induce weight loss, and can be broadly classified into lifestyle, pharmacological and surgical interventions. Lifestyle interventions will include those exploring diet, physical activity, exercise, or behavioural strategies used in isolation or in combination to reduce calorie intake and/or increase energy expenditure. Pharmacological inventions will include interventions using drugs, which act to reduce absorption or suppress appetite. Bariatric surgery interventions will include restrictive surgery designed to limit food intake (i.e. gastric banding or sleeve gastrectomy) or cause malabsorption (i.e. intestinal bypass) or both (i.e. gastric bypass). The review will include these interventions used alone or in combination.

How the intervention might work

Both surgical and non‐surgical weight loss interventions have been explored in CKD patients, and may play an important role in slowing the progression of CKD and its associated risk factors; diabetes, hypertension, dyslipidaemia and CVD (Ash 2006). While both weight loss interventions result in reductions in BMI, the magnitude is greater in those receiving surgical intervention (Bolignano 2013; Navaneethan 2009). Non‐surgical interventions have proven to be a successful and cost effective therapy in the CKD population; demonstrating short‐term weight reduction and corresponding improvements in systolic blood pressure (SBP), lipid profile and proteinuria (Bolignano 2013; Navaneethan 2009). However in practice many people are unable to maintain lifestyle change and regain lost body weight. Consequently these interventions may fail to achieve sustained weight loss, reductions in cardiorenal and metabolic risks and induce sufficient weight loss for transplant consideration in many obese patients (Weiner 2004). Bariatric surgery is currently considered the most effective weight loss intervention to achieve long‐term weight loss in morbidly obese individuals (Colquitt 2014); and has been evaluated in obese individuals with CKD as an approach to achieve sustained weight loss and improve kidney function (Chang 2017). Evidence from clinical studies have shown that weight loss achieved through bariatric surgery can reduce the effects of CKD by reducing glomerular hyperfiltration proteinuria, albuminuria, blood pressure, hyperglycaemia and may induce diabetes remission (Bolignano 2013; Chang 2017). This may have important clinical applications as early bariatric surgery may assist with reversal of diabetes, hypertension and glomerular hyperfiltration thereby preventing further kidney injury. This may delay the need for RRT, open up opportunities for kidney transplantation and decrease the significant health burden associated with obesity and CKD.

Why it is important to do this review

The incidences of obesity and CKD continue to escalate and are contributing to more global death, morbidity, disability and healthcare cost than ever before (Hill 2016). Whether weight loss can reverse these impacts however remains unclear and few practice guidelines exist regarding appropriate strategies for weight management in people with CKD (Lambert 2017). Reducing and managing obesity may reverse or slow CKD progression and enable transplantation as a treatment option for more individuals (Chang 2017; Lassalle 2017). However weight loss interventions in people with CKD are not without risk. Lifestyle interventions such as very low energy diets (VLED) may cause electrolyte disturbances, fluid overload, constipation, uraemia and blood glucose disturbances in diabetics (Lambert 2017). Weight loss medication used in CKD populations such as Orlistat may cause side effects including steatorrhoea, abdominal pain, flatulence, and increase the risk of oxalate nephropathy and kidney stones (Navaneethan 2009). Surgical interventions may be associated with higher rates of complications, such as band erosion, gastric leak and acute kidney injury (AKI) when compared with the non‐CKD population and surgeries featuring higher malabsorption appear to increase the risk of nephrolithiasis and oxalate nephropathy (Chang 2017; Weiner 2004). Furthermore highly restrictive diets post bariatric surgery can lead to dietary intakes well below recommended daily nutrient targets increasing risk of long‐term nutrient deficiencies (Colquitt 2014). This systematic review aims to provide a current and comprehensive review of weight reduction interventions in CKD by including both overweight and obese adults at all stages of CKD (including pre dialysis, dialysis, supportive care or kidney transplantation). This will provide a better understanding of the balance of benefits and harms of weight loss in CKD which will help better inform clinical decision‐making by clinicians, patients and their caregivers.

Objectives

To assess the efficacy of weight reduction interventions in overweight and obese adults with CKD; including those with ESKD being treated with dialysis, kidney transplantation, or conservative management.

Methods

Criteria for considering studies for this review

Types of studies

We will include randomised controlled trials (RCTs) and quasi RCTs (RCTs in which allocation to treatment was obtained by alternation, use of alternate medical records, date of birth or other predictable methods) looking at the efficacy of intentional weight loss interventions in adults with CKD.

Types of participants

Inclusion criteria

Adults who are overweight (as defined by BMI 25 to 29.9 kg/m2) or obese (as defined by BMI ≥ 30 kg/m2) (WHO 2017) with pre‐existing CKD defined by the Kidney Disease: Improving Global Outcomes (KDIGO 2013) "kidney damage for ≥3 months, as defined by structural or functional abnormalities of the kidney, with or without decreased GFR or GFR <60 mL/min/1.73m2 for ≥3 months, with or without kidney damage". The review will include individuals with CKD or ESKD treated with dialysis (both HD and PD), kidney transplantation, or supportive care.

Exclusion criteria

The review will exclude studies involving pregnant women, children (younger than 18 years) and people with AKI.

Types of interventions

We plan to investigate studies reporting on intentional weight loss interventions of at least four weeks in duration designed to promote weight loss as one of their primary stated goals, in any health care setting.

These studies will include

  • Lifestyle interventions, including dietary interventions (i.e. energy restricted diet, VLED), physical activity interventions (i.e. aerobic exercise, resistance exercise, group exercise programs), behavioural change interventions (strategies to assist with lifestyle modification i.e. self‐monitoring of eating habits, stress management), and combination lifestyle interventions (using any combination of diet, exercise and/or behavioural interventions).

  • Pharmacological interventions, including appetite suppressants, drugs that cause fat malabsorption of any dose and route, pharmacological plus lifestyle interventions.

  • Surgical interventions, including gastric sleeve, lap band, or bypass procedure.

Any of these interventions will be compared with any other intervention, placebo or usual care.

Types of outcome measures

Primary outcomes

  • Anthropometric measures (weight loss, body weight, BMI, waist circumference, waist‐to‐hip ratio and body composition)

  • Death (all causes)

  • Cardiovascular events.

Secondary outcomes

1. Clinical parameters

  • Kidney function measures: creatinine clearance (CrCl), serum creatinine (SCr), proteinuria, albuminuria, glomerular hyperfiltration (as defined and measured by study investigators)

  • Blood pressure: SBP and diastolic (DBP), anti‐hypertensive medication changes

  • Blood glucose: glycosylated haemoglobin (HbA1c), fasting blood glucose, hypoglycaemic medication changes

  • Lipid profile: total cholesterol, low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol, triglycerides, lipid lowering medication changes

  • Successful kidney transplantation

  • Inflammation (C‐reactive protein).

2. Patient‐centred outcomes using validated tools or self‐reported data

  • Adherence to treatment

  • Health‐related quality of life

  • Nutritional status

  • Dietary intake

  • Physical activity behaviours.

3. Cost effectiveness and economic analysis

  • Cost per DALYs or quality adjusted life year (QALY)

  • Cost associated with weight loss intervention.

4. Adverse events and potential harms

  • Hospitalisation

  • Adverse patient outcomes associated with each weight loss intervention

  • Biochemical adverse effects such as hyperkalaemia or hypophosphataemia.

Search methods for identification of studies

Electronic searches

We will search the Cochrane Kidney and Transplant Specialised Register through contact with the Information Specialist using search terms relevant to this review. The Cochrane Kidney and Transplant Specialised Register contains studies identified from several sources.

  1. Monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL)

  2. Weekly searches of MEDLINE OVID SP

  3. Handsearching of kidney‐related journals and the proceedings of major kidney conferences

  4. Searching of the current year of EMBASE OVID SP

  5. Weekly current awareness alerts for selected kidney and transplant journals

  6. Searches of the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

Studies contained in the Specialised Register are identified through search strategies for CENTRAL, MEDLINE, and EMBASE based on the scope of Cochrane Kidney and Transplant. Details of these strategies, as well as a list of hand searched journals, conference proceedings and current awareness alerts, are available in the Specialised Register section of information about Cochrane Kidney and Transplant.

See Appendix 1 for search terms used in strategies for this review.

Searching other resources

  1. Reference lists of review articles, relevant studies and clinical practice guidelines.

  2. Letters seeking information about unpublished or incomplete trials to investigators known to be involved in previous studies.

Data collection and analysis

Selection of studies

The search strategy described will be used to obtain titles and abstracts of studies that may be relevant to the review. The titles and abstracts will be screened independently by two authors who will discard studies that are not relevant; however studies and reviews that might include relevant data or information on trials will be retained initially. Two authors will independently assess retrieved abstracts, and if necessary the full text, of these studies to determine which studies satisfy the inclusion criteria. Any differences will be resolved by discussion and, where necessary, by consultation with a third author.

Data extraction and management

For studies that fulfil the inclusion criteria, data will be extracted by the same two independent authors using standard data extraction forms. Studies reported in non‐English language journals will be translated before assessment. Where more than one publication of one study exists, reports will be grouped together and the publication with the most complete data will be used in the analyses. Where relevant outcomes are only published in earlier versions, these data will be used. Any discrepancy between published versions will be highlighted. Disagreements that cannot be resolved through discussion between the two authors will be resolved in consultation with a third author.

Assessment of risk of bias in included studies

The following items will be independently assessed by two authors using the risk of bias assessment tool (Higgins 2011) (see Appendix 2).

  • Was there adequate sequence generation (selection bias)?

  • Was allocation adequately concealed (selection bias)?

  • Was knowledge of the allocated interventions adequately prevented during the study?

    • Participants and personnel (performance bias)

    • Outcome assessors (detection bias)

  • Were incomplete outcome data adequately addressed (attrition bias)?

  • Are reports of the study free of suggestion of selective outcome reporting (reporting bias)?

  • Was the study apparently free of other problems that could put it at a risk of bias?

Measures of treatment effect

For dichotomous outcomes (e.g. death, drop‐out rates), results will be expressed as risk ratio (RR) with 95% confidence intervals (CI). Where continuous scales of measurement are used to assess the effects of treatment (anthropometric and biochemical markers), the mean difference (MD) will be used, or the standardised mean difference (SMD) if different scales have been used.

Unit of analysis issues

Cluster‐randomised studies

Cluster‐randomised studies will be analysed in one of two ways.

Using a statistical analysis that properly accounts for the cluster design. Some examples of these are based on a ‘multi‐level model’, a ‘variance components analysis’ or may use ‘generalised estimating equations’ (Higgins 2011).

Conduct the analysis treating the sample size as the number of clusters and proceed as if the study was individually randomised, treating the clusters as individuals.

Cross‐over studies

Cross‐over studies will be analysed using only the data from the first period.

Studies with more than two treatment arms

When considering studies with multiple intervention groups we will try to combine all relevant experimental intervention groups of the study into a single group and to combine all relevant control intervention groups into a single group to enable single pair wise comparison.

Dealing with missing data

Any further information required from the original author will be requested by written correspondence (e.g. emailing corresponding author) and any relevant information obtained in this manner will be included in the review. Evaluation of important numerical data, such as screened, randomised patients as well as intention‐to‐treat, as‐treated and per‐protocol populations, will be carefully performed. Attrition rates, for example drop‐outs, losses to follow‐up and withdrawals will be investigated. Issues of missing data and imputation methods (for example, last‐observation‐carried‐forward) will be critically appraised (Higgins 2011).

Assessment of heterogeneity

We will first assess the heterogeneity by visual inspection of the forest plot. We will quantify statistical heterogeneity using the I2 statistic, which describes the percentage of total variation across studies that is due to heterogeneity rather than sampling error (Higgins 2003). A guide to the interpretation of I2 values will be as follows.

  • 0% to 40%: might not be important

  • 30% to 60%: may represent moderate heterogeneity

  • 50% to 90%: may represent substantial heterogeneity

  • 75% to 100%: considerable heterogeneity

The importance of the observed value of I2 depends on the magnitude and direction of treatment effects and the strength of evidence for heterogeneity (e.g. P‐value from the Chi2 test, or a confidence interval for I2) (Higgins 2011).

Assessment of reporting biases

If at least 10 studies are included in a meta‐analysis, we will generate a funnel plot to attempt to identify any publication bias in the included studies (Higgins 2011). We intend to assess funnel plot asymmetry through visual inspection. If asymmetry is suggested by a visual assessment, we will perform additional analyses to investigate it by using an Egger regression test to quantify the magnitude of asymmetry and a trim and fill analysis to assess the potential effect of funnel plot asymmetry on the estimated mean effect size (Higgins 2011).

Data synthesis

The specific method for pooling data will depend on the outcome measure. We will present the main outcomes and results organised by the types of interventions identified in the methods section. Depending on the assembled data, we may also investigate the possibility of organising the data by stage of CKD. Within each data category, we will explore the main comparisons of the review. If sufficient, similar studies (in terms of participants, interventions, comparison, outcome measures as determined by consensus) are available to ensure meaningful conclusions, we will pool their results in a meta‐analysis.

Data will be pooled using the random‐effects model but the fixed‐effect model will also be used to ensure robustness of the model chosen and susceptibility to outliers. If there is evidence of sizeable clinical, methodological, or statistical heterogeneity across included studies, we will not report pooled results from meta‐analysis, but instead will use a narrative approach to data synthesis.

Subgroup analysis and investigation of heterogeneity

Subgroup analysis will be used to explore possible sources of heterogeneity. If adequate data are available, we will perform subgroup analysis for the following.

  • BMI (overweight versus obese)

  • Stage of CKD and modality (HD, PD, transplantation, supportive care)

  • Duration of intervention (≤ 3 months versus > 3 months)

  • Chief causes of CKD, (diabetes, hypertension, glomerulonephritis, polycystic kidney disease, reflux kidney disease)

  • Presence or absence of proteinuria

Sensitivity analysis

If adequate data are available, we will perform sensitivity analyses in order to explore the influence of the following factors on effect size:

  • Repeating the analysis excluding unpublished studies;

  • Repeating the analysis taking account of risk of bias, as specified;

  • Repeating the analysis excluding any very long or large studies to establish how much they dominate the results; and

  • Repeating the analysis excluding studies using the following filters: diagnostic criteria, language of publication, source of funding (industry versus other), country.

'Summary of findings' tables

We will present the main results of the review in 'Summary of findings' tables. These tables present key information concerning the quality of the evidence, the magnitude of the effects of the interventions examined, and the sum of the available data for the main outcomes (Schunemann 2011a). The 'Summary of findings' tables also include an overall grading of the evidence related to each of the main outcomes using the GRADE (Grades of Recommendation, Assessment, Development and Evaluation) approach (GRADE 2008; GRADE 2011). The GRADE approach defines the quality of a body of evidence as the extent to which one can be confident that an estimate of effect or association is close to the true quantity of specific interest. The quality of a body of evidence involves consideration of within‐trial risk of bias (methodological quality), directness of evidence, heterogeneity, precision of effect estimates and risk of publication bias (Schunemann 2011b).

We plan to present the following outcomes in the 'Summary of findings' tables.

  1. Adverse events; death (all causes), and cardiovascular events

  2. Kidney function measures; CrCl and proteinuria/albuminuria

  3. Anthropometric measures specifically body weight, BMI and body composition

  4. Blood pressure: SBP and DBP

  5. Blood glucose: HbA1c and/or fasting blood glucose levels

  6. Lipid profile: total cholesterol, LDL , HDL, and triglycerides

  7. Adherence rates, quality of life, cost effectiveness; and, biochemical adverse effects such as hyperkalaemia or hypophosphataemia.

Acknowledgements

The authors wish to acknowledge the assistance of the Cochrane Kidney and Transplant’s Group editors and referees, and the information specialist.

Appendices

Appendix 1. Electronic search strategies

Database Search terms
CENTRAL

  1. MeSH descriptor: [Kidney Diseases] explode all trees

  2. MeSH descriptor: [Renal Replacement Therapy] explode all trees

  3. MeSH descriptor: [Renal Insufficiency] explode all trees

  4. MeSH descriptor: [Renal Insufficiency, Chronic] explode all trees

  5. dialysis:ti,ab,kw (Word variations have been searched)

  6. hemodialysis or haemodialysis:ti,ab,kw (Word variations have been searched)

  7. hemofiltration or haemofiltration:ti,ab,kw (Word variations have been searched)

  8. hemodiafiltration or haemodiafiltration:ti,ab,kw (Word variations have been searched)

  9. kidney disease* or renal disease* or kidney failure or renal failure:ti,ab,kw (Word variations have been searched)

  10. ESRF or ESKF or ESRD or ESKD:ti,ab,kw (Word variations have been searched)

  11. CKF or CKD or CRF or CRD:ti,ab,kw (Word variations have been searched)

  12. CAPD or CCPD or APD:ti,ab,kw (Word variations have been searched)

  13. predialysis or pre‐dialysis:ti,ab,kw (Word variations have been searched)

  14. {or #1‐#13}

  15. MeSH descriptor: [Weight Loss] this term only

  16. MeSH descriptor: [Weight Reduction Programs] this term only

  17. MeSH descriptor: [Body Weight] this term only

  18. MeSH descriptor: [Body Weight Changes] explode all trees

  19. MeSH descriptor: [Anti‐Obesity Agents] explode all trees

  20. MeSH descriptor: [Diet Therapy] explode all trees

  21. MeSH descriptor: [Energy Intake] explode all trees

  22. MeSH descriptor: [Behavior Therapy] explode all trees

  23. MeSH descriptor: [Food, Formulated] explode all trees

  24. calorie control*:ti,ab,kw (Word variations have been searched)

  25. calorie restrict*:ti,ab,kw (Word variations have been searched)

  26. weight loss:ti,ab,kw (Word variations have been searched)

  27. meal replacement*:ti,ab,kw (Word variations have been searched)

  28. weight reduc*:ti,ab,kw (Word variations have been searched)

  29. MeSH descriptor: [Exercise] explode all trees

  30. MeSH descriptor: [Exercise Therapy] explode all trees

  31. MeSH descriptor: [Gastric Bypass] this term only

  32. MeSH descriptor: [Gastroplasty] this term only

  33. gastric band*:ti,ab,kw (Word variations have been searched)

  34. gastric bypass:ti,ab,kw (Word variations have been searched)

  35. laparoscopic sleeve gastrectom*:ti,ab,kw (Word variations have been searched)

  36. {or #15‐#35}

  37. MeSH descriptor: [Obesity] explode all trees

  38. MeSH descriptor: [Overweight] this term only

  39. overweight*:ti,ab,kw (Word variations have been searched)

  40. obese or obesity:ti,ab,kw (Word variations have been searched)

  41. {or #37‐#40}

  42. {and #14, #36, #41}
MEDLINE

  1. Kidney Diseases/

  2. exp Renal Replacement Therapy/

  3. Renal Insufficiency/

  4. exp Renal Insufficiency, Chronic/

  5. Diabetic Nephropathies/

  6. exp Hypertension, Renal/

  7. dialysis.tw.

  8. (hemodialysis or haemodialysis).tw.

  9. (hemofiltration or haemofiltration).tw.

  10. (hemodiafiltration or haemodiafiltration).tw.

  11. (kidney disease* or renal disease* or kidney failure or renal failure).tw.

  12. (ESRF or ESKF or ESRD or ESKD).tw.

  13. (CKF or CKD or CRF or CRD).tw.

  14. (CAPD or CCPD or APD).tw.

  15. (predialysis or pre‐dialysis).tw.

  16. or/1‐15

  17. Weight Loss/

  18. body weight changes/

  19. Body Weight/

  20. Weight Reduction Programs/

  21. exp Anti‐Obesity Agents/

  22. exp Diet Therapy/

  23. exp Energy Intake/

  24. exp Behavior Therapy/

  25. exp Food, Formulated/

  26. calorie controlled.tw.

  27. calorie restrict$.tw.

  28. diet$.tw.

  29. weight loss.tw.

  30. weight reduc$.tw.

  31. meal replacement$.tw.

  32. exp Exercise/

  33. exp Exercise Therapy/

  34. Gastric Bypass/

  35. Gastroplasty/

  36. gastric band$.tw.

  37. gastric bypass.tw.

  38. laparoscopic sleeve gastrectom$.tw.

  39. or/17‐38

  40. exp Obesity/

  41. Overweight/

  42. Body Weight/

  43. overweight.tw.

  44. (obese or obesity).tw.

  45. or/41‐45

  46. and/16,39,45
EMBASE

  1. exp renal replacement therapy/

  2. kidney disease/

  3. chronic kidney disease/

  4. kidney failure/

  5. chronic kidney failure/

  6. mild renal impairment/

  7. stage 1 kidney disease/

  8. moderate renal impairment/

  9. severe renal impairment/

  10. end stage renal disease/

  11. renal replacement therapy‐dependent renal disease/

  12. diabetic nephropathy/

  13. kidney transplantation/

  14. renovascular hypertension/

  15. (hemodialysis or haemodialysis).tw.

  16. (hemofiltration or haemofiltration).tw.

  17. (hemodiafiltration or haemodiafiltration).tw.

  18. dialysis.tw.

  19. (CAPD or CCPD or APD).tw.

  20. (kidney disease* or renal disease* or kidney failure or renal failure).tw.

  21. (CKF or CKD or CRF or CRD).tw.

  22. (ESRF or ESKF or ESRD or ESKD).tw.

  23. (predialysis or pre‐dialysis).tw.

  24. ((kidney or renal) adj (transplant* or graft* or allograft*)).tw.

  25. or/1‐24

  26. weight reduction/

  27. weight loss program/

  28. body weight management/

  29. antiobesity agent/

  30. diet therapy/ or diet restriction/ or low calory diet/ or low fat diet/ or protein diet/

  31. (calorie controlled or calorie restrict$).tw.

  32. weight loss.tw.

  33. weight reduc$.tw.

  34. meal replacement$.tw.

  35. exp exercise/

  36. exp kinesiotherapy/

  37. stomach bypass/

  38. gastric band/

  39. gastric banding/

  40. sleeve gastrectomy/

  41. laparoscopic sleeve gastrectom$.tw.

  42. or/26‐41

  43. obesity/ or abdominal obesity/ or morbid obesity/

  44. overweight.tw.

  45. or/43‐44

  46. and/25,42,45
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Appendix 2. Risk of bias assessment tool

Potential source of bias Assessment criteria
Random sequence generation
Selection bias (biased allocation to interventions) due to inadequate generation of a randomised sequence		 Low risk of bias: Random number table; computer random number generator; coin tossing; shuffling cards or envelopes; throwing dice; drawing of lots; minimisation (minimisation may be implemented without a random element, and this is considered to be equivalent to being random).
High risk of bias: Sequence generated by odd or even date of birth; date (or day) of admission; sequence generated by hospital or clinic record number; allocation by judgement of the clinician; by preference of the participant; based on the results of a laboratory test or a series of tests; by availability of the intervention.
Unclear: Insufficient information about the sequence generation process to permit judgement.
Allocation concealment
Selection bias (biased allocation to interventions) due to inadequate concealment of allocations prior to assignment		 Low risk of bias: Randomisation method described that would not allow investigator/participant to know or influence intervention group before eligible participant entered in the study (e.g. central allocation, including telephone, web‐based, and pharmacy‐controlled, randomisation; sequentially numbered drug containers of identical appearance; sequentially numbered, opaque, sealed envelopes).
High risk of bias: Using an open random allocation schedule (e.g. a list of random numbers); assignment envelopes were used without appropriate safeguards (e.g. if envelopes were unsealed or non‐opaque or not sequentially numbered); alternation or rotation; date of birth; case record number; any other explicitly unconcealed procedure.
Unclear: Randomisation stated but no information on method used is available.
Blinding of participants and personnel
Performance bias due to knowledge of the allocated interventions by participants and personnel during the study		 Low risk of bias: No blinding or incomplete blinding, but the review authors judge that the outcome is not likely to be influenced by lack of blinding; blinding of participants and key study personnel ensured, and unlikely that the blinding could have been broken.
High risk of bias: No blinding or incomplete blinding, and the outcome is likely to be influenced by lack of blinding; blinding of key study participants and personnel attempted, but likely that the blinding could have been broken, and the outcome is likely to be influenced by lack of blinding.
Unclear: Insufficient information to permit judgement
Blinding of outcome assessment
Detection bias due to knowledge of the allocated interventions by outcome assessors.		 Low risk of bias: No blinding of outcome assessment, but the review authors judge that the outcome measurement is not likely to be influenced by lack of blinding; blinding of outcome assessment ensured, and unlikely that the blinding could have been broken.
High risk of bias: No blinding of outcome assessment, and the outcome measurement is likely to be influenced by lack of blinding; blinding of outcome assessment, but likely that the blinding could have been broken, and the outcome measurement is likely to be influenced by lack of blinding.
Unclear: Insufficient information to permit judgement
Incomplete outcome data
Attrition bias due to amount, nature or handling of incomplete outcome data.		 Low risk of bias: No missing outcome data; reasons for missing outcome data unlikely to be related to true outcome (for survival data, censoring unlikely to be introducing bias); missing outcome data balanced in numbers across intervention groups, with similar reasons for missing data across groups; for dichotomous outcome data, the proportion of missing outcomes compared with observed event risk not enough to have a clinically relevant impact on the intervention effect estimate; for continuous outcome data, plausible effect size (difference in means or standardised difference in means) among missing outcomes not enough to have a clinically relevant impact on observed effect size; missing data have been imputed using appropriate methods.
High risk of bias: Reason for missing outcome data likely to be related to true outcome, with either imbalance in numbers or reasons for missing data across intervention groups; for dichotomous outcome data, the proportion of missing outcomes compared with observed event risk enough to induce clinically relevant bias in intervention effect estimate; for continuous outcome data, plausible effect size (difference in means or standardized difference in means) among missing outcomes enough to induce clinically relevant bias in observed effect size; ‘as‐treated’ analysis done with substantial departure of the intervention received from that assigned at randomisation; potentially inappropriate application of simple imputation.
Unclear: Insufficient information to permit judgement
Selective reporting
Reporting bias due to selective outcome reporting		 Low risk of bias: The study protocol is available and all of the study’s pre‐specified (primary and secondary) outcomes that are of interest in the review have been reported in the pre‐specified way; the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre‐specified (convincing text of this nature may be uncommon).
High risk of bias: Not all of the study’s pre‐specified primary outcomes have been reported; one or more primary outcomes is reported using measurements, analysis methods or subsets of the data (e.g. sub‐scales) that were not pre‐specified; one or more reported primary outcomes were not pre‐specified (unless clear justification for their reporting is provided, such as an unexpected adverse effect); one or more outcomes of interest in the review are reported incompletely so that they cannot be entered in a meta‐analysis; the study report fails to include results for a key outcome that would be expected to have been reported for such a study.
Unclear: Insufficient information to permit judgement
Other bias
Bias due to problems not covered elsewhere in the table		 Low risk of bias: The study appears to be free of other sources of bias.
High risk of bias: Had a potential source of bias related to the specific study design used; stopped early due to some data‐dependent process (including a formal‐stopping rule); had extreme baseline imbalance; has been claimed to have been fraudulent; had some other problem.
Unclear: Insufficient information to assess whether an important risk of bias exists; insufficient rationale or evidence that an identified problem will introduce bias.
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Contributions of authors

  1. Draft the protocol: MC, CM, KC, HM, DJ

  2. Study selection: MC, CM

  3. Extract data from studies: MC, CM

  4. Enter data into RevMan: MC, CM

  5. Carry out the analysis: MC

  6. Interpret the analysis: MC, CM, KC, HM, DJ

  7. Draft the final review: MC, CM, KC, HM, DJ

  8. Disagreement resolution: KC

  9. Update the review: MC

Declarations of interest

  • Marguerite Conley: none known

  • Catherine McFarlane: none known

  • David Johnson: none known

  • Katrina Campbell: none known

  • Helen MacLaughlin: none known

New

References

Additional references

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