Evidence Mapping of Whole Grain Intervention Studies, Health Outcomes, and Reporting Practices
Authors: Sawicki Caleigh M. , Livingston Kara A. , Jacques Paul F. , Koecher Katie , McKeown Nicola M. 
Published: November 2023

Higher consumption of whole grain foods is associated with reduced risk of cardiovascular disease, diabetes, and obesity in observational studies; yet, in intervention studies, the effect of whole grains on intermediate markers of risk are mixed. This may be due to the variability in study design, differences in composition of different grains, degree of processing, and the definition of the whole grain intervention. Therefore, the aim of this project was to use evidence mapping to capture and summarize the methodological differences in whole grain intervention studies. We conducted a reproducible search in OVID Medline using a broad list of whole grain keywords to identify potentially relevant intervention studies. The search extended from inception of the Medline database (1946) to November 2015 and was restricted to human interventions published in English. After a two‐step screening process, which included abstract and then full text screening, we identified 170 relevant publications which described a total of 180 whole grain interventions. Over half (57%, n=102) were acute interventions, lasting ≤1 day, while 43% (n=78) were of longer duration, lasting from 2 days to 2 years (mean ± SD = 54.3 ± 75.4 days). The majority of the acute interventions (75%, n=77) examined measures of glycemia and/or insulinemia, while the most frequent outcomes studied in the longer interventions included measures of cardiometabolic health (68%, n=53), anthropometrics (60%, n=47), and measures of appetite/satiety (55%, n=43). Although the whole grains provided were described to varying degrees, most publications (85%, n=145) did not define whole grains. Of those that did provide a definition only 4% (n=7) referenced an established definition, such as from the American Association of Cereal Chemists, while the remaining 11% provided various general definitions. With respect to the longer‐duration diet interventions, 38% (n=30) were full whole‐grain substitution interventions (all servings of grains were whole grain), 40% (n=31) were partial substitution (providing ~2 servings or more/day), and 22% (n=17) were single food (~1 serving/day) interventions. When reporting the whole grain doses administered in these studies, 53% (n=41) reported the actual amount of whole grains (in grams or servings), 41% (n=32) reported the amount of food/product (thus providing no actual whole grain amount), and 6% (n=5) did not report a dose at all. Among the interventions that provided a variety of whole grains, less than half (43%, n=9) reported the distribution of the different grains in the diet. There was also variability in reporting of subject compliance, and only 21% (n=16) used independent biomarkers of whole grain intake. This evidence map highlights the need for improved and standardized reporting practices, such as for the amount and type of whole grains and degree of study compliance, allowing for effective synthesis to better inform nutrition scientists and public health policy.

Support or Funding Information

Funding support for this project was provided by the Bell Institute of Health and Nutrition, General Mills Inc.