Evaluating Whole Grain Intervention Study Designs and Reporting Practices Using Evidence Mapping Methodology

Abstract

Consumption of whole grains have been associated with reduced risk of chronic diseases in many observational studies; yet, results of intervention studies are mixed. We aimed to use evidence mapping to capture the methodological and reporting variability in whole grain intervention studies that may contribute to this inconsistency. We conducted a reproducible search in OVID Medline for whole grain human intervention studies (published 1946 to February 2018). After screening based on a priori criteria, we identified 202 publications describing a total of 213 unique trials. Over half (55%) were acute trials, lasting ≤1 day, 30% were moderate duration studies (up to 6 weeks) and 15% were of longer duration (more than 6 weeks). The majority of acute trials (75%) examined measures of glycaemia and/or insulinemia, while most of the longer trials included measures of cardiometabolic health (71%), appetite/satiety (57%) and weight/adiposity (56%). Among the moderate and long duration trials, there was a wide range of how whole grains were described but only 10 publications referenced an established definition. Only 55% of trials reported the actual amount of whole grains (in grams or servings), while 36% reported the amount of food/product and 9% did not report a dose at all. Of the interventions that provided a mixture of whole grains, less than half (46%) reported the distribution of the different grain types. Reporting of subject compliance also varied and only 22% used independent biomarkers of whole grain intake. This evidence map highlights the need to standardize both study protocols and reporting practices to support effective synthesis of study results and provide a stronger foundation to better inform nutrition scientists and public health policy.

The Effects of Intact Cereal Grain Fibers, Including Wheat Bran on the Gut Microbiota Composition of Healthy Adults: A Systematic Review

“…Sawicki et al (71) took an Evidence Mapping approach to explore the influence of dietary fiber on the human gut microbiota. This mapping exercise highlighted that much of the current literature has shown positive effects of dietary fiber on gut function or beneficial bacterial species, or positive effects of dietary fiber on specific health outcomes, but few seem to be directly measuring these outcomes together, to provide evidence of a dietary fiber-modulated gut microbiota and health outcome.…”

The Relationship between Whole Grain Intake and Body Weight: Results of Meta-Analyses of Observational Studies and Randomized Controlled Trials

“…An additional consideration is variation in the definitions of WG foods used in both RCTs and observational studies [22]. In 2006, the United States Food and Drug Administration adopted a WG definition that includes intact, ground, cracked, or flaked fruit of grains whose principal components (the starchy endosperm, germ, and bran) are present in the same relative proportions as in the intact grain [22]. Prior to that, some studies included bran and other high dietary fiber foods in their definitions of WG [75].…”

“…After full text reviews were completed, PICO (population, intervention, comparator, and outcome) data and results were extracted from eligible publications into one of two databases (one for intervention studies, one for observational studies) that were created with input from the research team. For the intervention study database PICO information was extracted, and then the database was searched for and restricted to studies with anthropometric outcomes of interest for the meta-analysis [22]. The observational database was created later, with the goal of a meta-analysis already established; thus, entries were only included in the database if they had the anthropometric outcomes of interest (per inclusion criteria stated above).…”

Evidence mapping to assess the available research on fiber, whole grains, and health

“…However, approximately 1500 publications were eliminated during abstract and full-text screening, leaving just over 200 eligible publications for inclusion in the final database. Inclusion and exclusion criteria are discussed in detail in a 2018 study by Sawicki et al 8 …”

“…The plot illustrates that the majority of studies were mid- to long-term trials exploring the effect of oats on cardiometabolic endpoints. The fully updated evidence map and weighted scatter plot are available in the report of Sawicki et al 8 …”