The relationship between whole grain intake and body weight: results of meta-analyses of observational studies and randomized controlled trials

Authors: MAKI, KEVIN - Midwest Biomedical Research; PALACIOS, ORSOLYA - Midwest Biomedical Research; KOECHER, KATIE - General Mills, Inc; SAWICKI, CALEIGH - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; LIVINGSTON, KARA - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; BELL, MARJORIE - Midwest Biomedical Research; CORTES, HEATHER - Kyzo Nutrition, Llc; MCKEOWN, NICOLA - Jean Mayer Human Nutrition Research Center On Aging At Tufts University

Submitted to: Nutrients
Publication Type: Review Article
Publication Acceptance Date: 5/27/2019
Publication Date: 5/31/2019
Citation: Maki, K.C., Palacios, O.M., Koecher, K., Sawicki, C., Livingston, K.A., Bell, M., Cortes, H.N., McKeown, N.M. 2019. The relationship between whole grain intake and body weight: results of meta-analyses of observational studies and randomized controlled trials. Nutrients. 11(6):1245. https://doi.org/10.3390/nu11061245.
DOI: https://doi.org/10.3390/nu11061245

Interpretive Summary: Whole grain (WG) foods are higher in fiber and other nutrients than refined grain foods, and higher intakes of WG have been related to lower risk of weight gain and obesity development. Generally, Americans are not meeting the current recommendations for WG consumption. Given that the majority of Americans are overweight or obese, it may be beneficial to emphasize a shift from refined grain to WG. In order to support this recommendation, we aimed to provide an updated review and synthesis of results from both observational studies and randomized controlled trials (RCTs) examining the relationship between WG intake and body weight status. A comprehensive literature search was conducted to identify relevant publications. A meta-analysis is a statistical technique used to synthesize data from several studies that used similar methods. Because the prospective cohort studies identified used different methods, the results from those study designs were assessed qualitatively. However, results from cross-sectional studies and RCTs were assessed through meta-analysis. Review of the 6 prospective cohort studies generally showed that higher WG intake lead to less weight gain over time, with follow-up time ranging from 5 to 10 years. The meta-analysis of cross-sectional data from 12 studies supported this conclusion, with results indicating that higher WG intake was significantly associated with lower body mass index. However, results from meta-analysis of 8 RCTs did not find a significant association between WG intake and change in body weight.

Technical Abstract: Results from some observational studies suggest that higher whole grain (WG) intake is associated with lower risk of weight gain. Ovid Medline was used to conduct a literature search for observational studies and randomized, controlled trials (RCTs) assessing WG food intake and weight status in adults. A meta-regression analysis of cross-sectional data from 12 observational studies (136,834 subjects) and a meta-analysis of 9 RCTs (973 subjects) was conducted; 6 prospective cohort publications were qualitatively reviewed. Cross-sectional data meta-regression results indicate a significant, inverse correlation between WG intake and body mass index (BMI): weighted slope-0.0141 kg/m^2 per g/d of WG intake [95% confidence interval (CI): -0.0207, -0.0077; r = -0.526, p = 0.0001]. Prospective cohort results generally showed inverse associations between WG intake and weight change with typical follow-up periods of 5 to 20 years. RCT meta-analysis results show a non-significant pooled standardized effect size of -0.049 kg (95% CI -0.297, 0.199, p = 0.698) for mean difference in weight change (WG versus control interventions). Higher WG intake is significantly inversely associated with BMI in observational studies but not RCTs up to 16 weeks in length; RCTs with longer intervention periods are warranted.