Meta-analyses of the Effect of Dietary Pulses on Acute Postprandial Metabolic Control

Overview

Dietary pulses (beans, peas, chickpeas, and lentils), more commonly known as "legumes", are generally recognized as healthy components of the diet. Canada's Food Guide encourages consumptions of meat alternatives, such as beans "more often"; and the dietary guidelines for Americans both recommend consumption of 3 cups of legumes per week. However, there remains insufficient information on the usefulness of these foods in protecting heart health. To improve evidence-based guidance for dietary pulse recommendations, the investigators propose to conduct a systematic review of the effect of dietary pulse consumption on after-meal blood sugar levels, appetite, and food intake regulation to help explain their mechanism for improving longterm blood sugar and body weight control. The systematic review process allows the combining of the results from many small studies in order to arrive at a pooled estimate, similar to a weighted average, of the true effect. The investigators will be able to explore whether eating pulses has different effects between men and women, in different age groups and background disease states, and whether or not the effect of pulses depends on the dose and background diet. The findings of this proposed knowledge synthesis will help improve the health of Canadians through informing recommendations for the general public, as well as those at risk of heart disease and diabetes.

Background: Pulses, including dry peas, beans, lentils and chickpeas, are a rich source of a number of healthy dietary components including dietary fiber, low glycemic index carbohydrate, vegetable protein and polyphenolics. To support health claims and evidence-based dietary guidelines, it is important to establish whether the glycemic control and weight loss benefits observed with dietary pulses are attributable to their proposed mechanism-of-action, whereby they reduce acute postprandial excursions in glycemia and contribute to satiety and decreased intake at subsequent meals. Objectives: The objective of this project is to conduct two systematic reviews and meta-analyses of the effect of dietary pulse consumption on acute postprandial metabolic endpoints: (1) postprandial glycemia and (2) food intake regulation. Design: The planning and conduct of the proposed meta-analyses will follow the Cochrane handbook for systematic reviews of interventions. The reporting will follow the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. Data sources: MEDLINE, EMBASE, CINAHL and The Cochrane Central Register of Controlled Trials will be searched using appropriate search terms. Study selection: Acute, single bolus controlled feeding trials that investigate the effect of isocaloric exchange of dietary pulses for other carbohydrate foods on cardiometabolic risk outcomes in humans will be included. Studies that have a chronic feeding design, lack a control, or report comparisons not matched for available carbohydrate will be excluded. Data extraction: Independent investigators (≥2) will extract information about study design, sample size, subject characteristics, pulse form, dose, follow-up, and the composition of the background diets. Mean±SEM values will be extracted for all outcomes. Standard computations and imputations will be used to derive missing variance data. Risk of bias and study quality will be assessed using the Cochrane Risk of Bias Tool and the Heyland Methodological Quality Score (MQS), respectively. Outcomes: Each analysis will assess a different set of endpoints related to acute postprandial metabolic control: (1) postprandial glycemia (area under the curve \[AUC\], GI) and (2) food intake regulation (subjective appetite scores, 2nd meal intake). Data synthesis: Separate pooled analyses will be conducted for each area of metabolic control using the Generic Inverse Variance method with random effects models. Random-effects models will be used even in the absence of statistically significant between-study heterogeneity, as they yield more conservative summary effect estimates in the presence of residual heterogeneity. Paired analyses will be applied to all crossover trials. Heterogeneity will be tested by Cochrane's Q and quantified by I2. Sources of heterogeneity will be explored by sensitivity and subgroup analyses. A priori subgroup analyses will include disease status, duration of test, pulse type, pulse dose, study design, study quality, baseline values, and change in fat, protein, and dietary fibre intake. Standard GI methodology compliance will be another a priori sungroup analysis for the postprandial glycemia analyses only. Significant unexplained heterogeneity will be investigated by additional post hoc subgroup analyses (e.g. age, sex, level of feeding control \[metabolic, supplemented, dietary advice\], washout in crossover trials, energy balance of the background diet, composition of the background diet \[total % energy from fat, carbohydrate, protein\], change in cholesterol intake, change in glycemic index, etc.). Meta-regression analyses will assess the significance of subgroups analyses. Publication bias will be investigated by the inspection of funnel plots and application of Egger's and Begg's tests. Knowledge translation plan: Results will be disseminated through traditional means such as interactive presentations at local, national, and international scientific meetings and publication in high impact factor journals. Innovative means such as webcasts with e-mail feedback mechanisms will also be used. Knowledge Users will act as knowledge brokers networking among opinion leaders and different adopter groups to increase awareness at each stage. Four Knowledge Users will also participate directly as members of nutrition guidelines committees. Target adopters will include the clinical practice, public health, industry, research communities, and patient groups. Feedback will be incorporated and used to guide analyses and improve key messages at each stage. Preliminary findings: We conducted a systematic review and meta-analysis of the effect of dietary pulses on glycemic control in 41 controlled feeding trials. We found that pulses alone or in low-glycemic index or high-fibre diets improved markers of glycemic control. Although the improvement was clinically significant, it came at the expense of substantial inter-study heterogeneity. Knowledge translation from this preliminary project has already begun. It has provided a rationale for a large trial of the effect of pulses in type 2 diabetes to address some of the identified sources of heterogeneity and is being used in the development of the 2013 CDA Clinical Practice Guidelines (CPG) for Nutrition Therapy. Significance: The proposed project will demonstrate that the improvement in longterm glycemic control seen in our previous systematic review and meta-analysis of longterm randomized controlled feeding trials of pulses can be attributed to acute reductions in postprandial glycemia, reductions in appetite, and decreased intake at subsequent meals. This demonstration will aid in knowledge translation related to the effects of dietary pulses on cardiometabolic risk, strengthening the evidence-base for dietary recommendations and health claims and improving health outcomes through informing healthcare providers and patients, stimulating industry innovation, and guiding future research.