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Effect of non-oil-seed pulses on glycaemic control: a systematic review and meta-analysis of randomised controlled experimental trials in people with and without diabetes |
Sievenpiper JL, Kendall CW, Esfahani A, Wong JM, Carleton AJ, Jiang HY, Bazinet RP, Vidgen E, Jenkins DJ |
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CRD summary The authors concluded that dietary non-oilseed pulses modestly improved medium to longer term glycaemic control when used alone or in low-glycaemic-index or high-fibre diets. Although this was a well-conducted review, the presence of publication bias and statistically significant heterogeneity mean the authors' conclusion may not be reliable. Authors' objectives To determine the effect of non-oilseed pulses, alone or as part of a low-glycaemic-index diet or high-fibre diet, on glycaemic control. Searching MEDLINE, EMBASE, CINAHL and the Cochrane Library were searched, with no language restrictions, up to May 2008. Search terms were reported. Unspecified handsearching was also performed. Study selection Eligible for inclusion in the review were randomised controlled trials (RCTs), with medium- to long-term follow-up, that investigated supplementing the diet with non-oilseed pulses in food form, alone or as part of a low-glycaemic-index diet or a high-fibre diet, compared with a non-pulse control.
Trials were excluded from the review if they: had a follow-up of less than seven days; contained oilseed pulses (peanuts or soy bean) or non-oilseed pulses in extract or tablet/capsule form; lacked a suitable control intervention; or they reported unbalanced or hyperenergetic comparisons.
Outcomes of interest included: glycosylated blood protein (glycosylated haemoglobin (HbA1c) or fructosamine, with HbA1c preferred if the duration of the trial was longer than 12 weeks); fasting blood glucose and fasting blood insulin concentrations; and homeostasis model assessment estimated insulin resistance (HOMA-IR).
Types of non-oilseed pulses in included trials were: black, white, pinto, red and white kidney beans; chickpeas; fava beans; and black-eyed peas in whole, flour or fibre form. Background diets were largely high-carbohydrate/low-fat diets. Characteristics for participants in terms of whether they had diabetes, hypercholesterolaemia or coronary artery disease varied between trials.
The authors did not state how many reviewers performed the study selection. Assessment of study quality Study quality was assessed using the Heyland score, which assigned a score for the following nine categories: study design (randomisation, blinding, protocol analysis), sampling procedures (selection, compatibility, follow-up), and interventions (protocol description, cointerventions, crossovers), with a maximum score of 13 points. Scores of 8 points or above were considered to be of high quality.
Two reviewers independently assessed study quality, with disagreements resolved by consensus or discussions with a third reviewer. Data extraction Data were extracted in order to calculate standardised mean differences (SMD) and 95% confidence intervals (CI).
Two reviewers independently performed data extraction using a standardised form. Any disagreements were resolved by consensus or by discussion with a third reviewer. Methods of synthesis Standardised mean differences were combined using a fixed-effect model or a random-effects model. The latter was used if significant heterogeneity was present. Heterogeneity was assessed using the X2 and I2 tests. Separate meta-analyses were performed for pulses alone, pulses in low-glycaemic-index diet, and pulses in high-fibre diets. Publication bias was assessed using funnel plots. A priori subgroup analyses included: participant category (normoglycaemia, type 1 diabetes, type 2 diabetes, any diabetes), pulse type, dosage, follow-up period and trial quality. Additional post hoc sub group analyses were also performed. Results of the review Thirty-nine RCTs (n=1,656 participants) were included in the review. There was limited evidence of publication bias for fasting blood glucose and fasting blood insulin, but no evidence for homeostasis model assessment estimated insulin resistance (HOMA-IR) or glycosylated blood protein. Follow-up ranged from seven days to three years, with the majority of studies having a follow-up period of less than 12 months.
Pulses alone (10 RCTs, n=253 participants): Trial quality ranged from 4 to 9 points, with four trials considered as high quality. Pulses alone was associated with a statistically significant decrease in fasting blood glucose (SMD -0.82, 95% C -1.36 to -0.27) and fasting blood insulin (SMD -0.49, 95% CI -0.93 to -0.04). There was no statistically significant difference in HOMA-IR and glycosylated blood protein. However, there was evidence of statistically significant heterogeneity (I2≥75%) for fasting blood glucose, fasting blood insulin and HOMA-IR.
Pulses in low glycaemic index diet (19 RCTs, n=762 participants): Trial quality ranged from 5 to 8 points, with 10 trials considered as high quality. Pulses in a low glycaemic index diet were associated with a statistically significant decrease in glycosylated blood protein (SMD: -0.28, 95% CI -0.42 to -0.14). There was no statistically significant difference in fasting blood glucose, fasting blood insulin and HOMA-IR. There was evidence of statistically significant heterogeneity (I2≥50%) for all outcomes except fasting blood insulin.
Pulses in high fibre diets (10 RCTs, n=641 participants): Trial quality ranged from 3 to 9 points, with six trials considered high quality. Pulses in a high fibre diet were associated with a statistically significant decrease in fasting blood glucose (SMD -0.32, 95% CI -0.49 to -0.15) and glycosylated blood protein (SMD -0.27, 95% CI -0.45 to -0.09). However, there was evidence of statistically significant heterogeneity (I2≥75%) for both analyses. There was no statistically significant difference in fasting blood insulin and HOMA-IR.
Diabetes status, pulse type, dose, physical form, duration of follow-up, study quality, macronutrient profile of background diets, feeding control and design were all sources of heterogeneity. Authors' conclusions Dietary non-oilseed pulses modestly improved medium to longer term glycaemic control when used alone or in low-glycaemic-index or high-fibre diets. CRD commentary The review addressed a clear research question which was supported by detailed inclusion criteria. The search strategy was adequate and with no language restrictions, which reduced the risk of language bias. However, there was no apparent search for unpublished material, which meant that relevant studies might have been missed. This was supported by the asymmetry observed in the funnel plots used to assess publication bias (funnel plots available online in supplementary material, Fig.1, for link see URL for Additional Data). The validity assessment tool was appropriate to the included study design. Adequate details of primary trials were provided. Methods of synthesis were appropriate and sources of heterogeneity were explored. The review process was generally carried out with sufficient attempts to minimise reviewer error and bias, but it was unclear how many reviewers performed the study selection. Although this was a generally well-conducted review, the presence of publication bias and statistically significant heterogeneity mean the authors' conclusion may not be reliable. Implications of the review for practice and research Practice: The authors did not state any implications for practice
Research: The authors stated that there is a need for large, well designed, carefully conducted randomised controlled trials with sufficiently long-term follow-up that investigate sources of heterogeneity such as diabetes status, pulse type, dose, physical form, follow-up, study quality, macronutrient profile of background diets and feeding control. Funding Canadian Institutes of Health Research Doctoral Research Award; Eddie Steinberg Scholarship Fund; Edward Christie Stevens Fellowship in Medicine; Government of Canada; Province of Canada Postdoctoral Fellowship; Pulse Canada. Bibliographic details Sievenpiper JL, Kendall CW, Esfahani A, Wong JM, Carleton AJ, Jiang HY, Bazinet RP, Vidgen E, Jenkins DJ. Effect of non-oil-seed pulses on glycaemic control: a systematic review and meta-analysis of randomised controlled experimental trials in people with and without diabetes. Diabetologia 2009; 52(8): 1479-1495 Indexing Status Subject indexing assigned by NLM MeSH Blood Glucose /drug effects /metabolism; Diabetes Mellitus /blood /diet therapy; Dietary Fats /pharmacology; Dietary Fiber /pharmacology; Glycemic Index /drug effects; Humans; Insulin /blood; Patient Selection; Randomized Controlled Trials as Topic; Reference Values; Research Design AccessionNumber 12009107872 Date bibliographic record published 11/11/2009 Date abstract record published 20/01/2010 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. |
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