Umbrella Review and Updated Systematic Review and Meta-analysis of Pulses/Legumes and Incident Cardiometabolic Diseases

Background: Dietary pulses, the edible dried seeds of legumes, are high in fiber, plant protein, and various micronutrients and low in fat and glycemic index (GI), have shown a wide range of health benefits for the prevention and management of type 2 diabetes and cardiovascular disease. However, dietary pulses are not well recognized for these advantages. Recommendations for dietary pulse intake vary across chronic disease guidelines. In specific, the European Association for the Study of Diabetes (EASD) guidelines for nutrition therapy have not made any specific recommendations regarding dietary pulses. The present umbrella review and updated systematic review and meta-analysis using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach was thus commissioned by the Diabetes and Nutrition Study Group (DNSG) of the EASD to summarize the available evidence from prospective cohort studies of the association between dietary pulses/legumes and cardiometabolic disease outcomes (incident cardiovascular diseases, diabetes, hypertension and overweight/obesity).

Need for proposed research: High quality systematic reviews and meta-analyses represent the highest level of evidence to support dietary guidelines and public health policy development. As dietary guidelines and public health policy have shifted toward food and dietary-pattern based recommendations, there is a need for a systematic review and meta-analysis assessing the pooled association between dietary pulses/legumes and cardiometabolic disease outcomes.

Objective: The investigators will conduct an umbrella review and updated systematic review and meta-analysis to summarize the association between dietary pulses/legumes and cardiometabolic disease outcomes in prospective cohort studies.

Design: The umbrella review will consist of a literature search of the most recent and/or comprehensive systematic reviews and meta-analyses published in this area. The included systematic reviews and meta-analyses will be updated conducting a systematic search for prospective cohort studies published after the census dates of the included systematic reviews and meta-analyses. The planning and conduct of the updated systematic review and meta-analysis will follow the Cochrane handbook for systematic reviews of interventions. The reporting will follow the Meta-analysis Of Observational Studies in Epidemiology (MOOSE) guidelines.

Data sources:

The umbrella review will consist of searching PubMed databases using appropriate search terms to identify the most recent and/or comprehensive systematic reviews and meta-analyses published in this area. The updated systematic review and meta-analysis will consist of searching MEDLINE, EMBASE, and The Cochrane Central Register of Controlled Trials after the census dates of the included systematic reviews and meta-analyses from the umbrella review using appropriate search terms supplemented by manual searches of references of included studies. Authors will be contacted for applicable missing data.

Study selection:

The umbrella review will include the most recent and/or comprehensive systematic reviews and meta-analyses of prospective cohort studies assessing the association between pulse/legume intake and cardiometabolic diseases outcomes (cardiovascular diseases, diabetes, hypertension, overweight/obesity). The updated systematic review and meta-analysis will include prospective cohort studies ≥1 year assessing the association between pulse/legume intake and cardiometabolic diseases outcomes (cardiovascular diseases, diabetes, hypertension, overweight/obesity) published since the last census dates of the included systematic reviews and meta-analyses from the umbrella review.

Data extraction: Data from prospective cohort studies in the most recent and/or comprehensive systematic reviews and meta-analyses will be included in the updated systematic review and meta-analysis. For newly identified prospective cohort studies, two or more investigators will independently extract relevant data and assess risk of bias using the Newcastle-Ottawa Scale (NOS) for observational studies. Risk ratios, odds ratios and hazard ratios for clinical outcomes will be extracted or derived from clinical event data across quantiles of exposure. All disagreements will be resolved by consensus.

Outcomes: The primary outcome of the systematic review and meta-analysis will be incident cardiovascular disease. Secondary outcomes will include incident coronary heart disease, stroke, diabetes, hypertension and overweight/obesity.

Data synthesis: The natural log-transformed relative risks of outcomes comparing the exposure to the reference group from each cohort will be pooled using the generic inverse variance method with random effects models and expressed as risk ratios (RR) with 95% confidence intervals (CIs). Heterogeneity will be assessed by Cochran Q statistic and quantified by I2. The significance level will be set at p<0.10 and an I2≥ 50% will be considered evidence of substantial heterogeneity. To explore sources of heterogeneity, the investigators will conduct sensitivity analyses, in which each study is systematically removed with recalculation of the summary estimates. If there are ≥10 studies, then the investigators will also explore sources of heterogeneity by a priori subgroup analyses (cohorts, sex, health status, follow-up [<10-years, ≥10-years], dose, level of adjustment of models, quality of the studies (NOS), and validation of the dietary assessment instruments). Meta-regression analyses will be used to assess the significance of categorical and continuous subgroups analyses. If there are ≥10 studies available, publication bias will be assessed by the visual inspection of funnel plots and formal testing using Begg's and Egger's tests. If publication bias is suspected, then the investigators will attempt to adjust for funnel plot asymmetry by imputing the missing study data using the Duval and Tweedie trim and fill method.

Evidence Assessment: The certainty of the evidence for each outcome will be assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

Knowledge translation plan: The results will be disseminated through interactive presentations at local, national, and international scientific meetings and publication in high impact factor journals. Target audiences will include the public health and scientific communities with interest in nutrition, diabetes, obesity, and cardiovascular disease. Feedback will be incorporated and used to improve the public health message and key areas for future research will be defined. Applicant/Co-applicant Decision Makers will network among opinion leaders to increase awareness and participate directly as committee members in the development of future guidelines.

Significance: The proposed project will aid in knowledge translation related to the role of dietary pulses in cardiometabolic disease risk, strengthening the evidence-base for guidelines and improving health outcomes by educating healthcare providers and patients, stimulating industry innovation, and guiding future research design.