Greater whole-grain intake is associated with lower risk of type 2 diabetes, cardiovascular disease, and weight gain

Abstract

Whole-grain and high fiber intakes are routinely recommended for prevention of vascular diseases; however, there are no comprehensive and quantitative assessments of available data in humans. The aim of this study was to systematically examine longitudinal studies investigating whole-grain and fiber intake in relation to risk of type 2 diabetes (T2D), cardiovascular disease (CVD), weight gain, and metabolic risk factors. We identified 45 prospective cohort studies and 21 randomized-controlled trials (RCT) between 1966 and February 2012 by searching the Cumulative Index to Nursing and Allied Health Literature, Cochrane, Elsevier Medical Database, and PubMed. Study characteristics, whole-grain and dietary fiber intakes, and risk estimates were extracted using a standardized protocol. Using random effects models, we found that compared with never/rare consumers of whole grains, those consuming 48-80 g whole grain/d (3-5 serving/d) had an ~26% lower risk of T2D [RR = 0.74 (95% CI: 0.69, 0.80)], ~21% lower risk of CVD [RR = 0.79 (95% CI: 0.74, 0.85)], and consistently less weight gain during 8-13 y (1.27 vs 1.64 kg; P = 0.001). Among RCT, weighted mean differences in post-intervention circulating concentrations of fasting glucose and total and LDL-cholesterol comparing whole-grain intervention groups with controls indicated significantly lower concentrations after whole-grain interventions [differences in fasting glucose: -0.93 mmol/L (95% CI: -1.65, -0.21), total cholesterol: -0.83 mmol/L (-1.23, -0.42); and LDL-cholesterol: -0.82 mmol/L (-1.31, -0.33)]. [corrected] Findings from this meta-analysis provide evidence to support beneficial effects of whole-grain intake on vascular disease prevention. Potential mechanisms responsible for whole grains' effects on metabolic intermediates require further investigation in large intervention trials.

FIGURE 1

Multivariable-adjusted RR of T2D (A) and CVD (B) comparing the highest and lowest categories of whole-grain intake in prospective cohort studies. Squares indicate the RR estimate in each study. The size of the square is proportional to the weight of each study in the overall random effects estimate. The horizontal line represents the 95% CI. The overall summary estimate and its 95% CI are indicated by the open diamond. I² = 0.0%, P = 0.44 for T2D; I² = 0.0%, P = 0.82 for CVD. CVD, cardiovascular disease; T2D, type 2 diabetes.

FIGURE 2

Multivariable-adjusted RR of T2D (A) and CVD (B) comparing the highest and lowest categories of dietary fiber intake in prospective cohort studies. Squares indicate the RR estimate in each study. The size of the square is proportional to the weight of each study in the overall random effects estimate. The horizontal line represents the 95% CI. The overall summary estimate and its 95% CI are indicated by the open diamond. I² = 44.1%, P = 0.04 for T2D; I² = 21.0%, P = 0.19 for CVD. CVD, cardiovascular disease; T2D, type 2 diabetes.

FIGURE 3

Multivariable-adjusted RR of T2D (A) and CVD (B) comparing the highest and lowest categories of dietary cereal fiber intake in prospective cohort studies. Squares indicate the RR estimate in each study. The size of the square is proportional to the weight of each study in the overall random-effects estimate. The horizontal line represents the 95% CI. The overall summary estimate and its 95% CI are indicated by the open diamond. I² = 73.6%, P < 0.001 for T2D; I² = 61.3%, P = 0.003 for CVD. CVD, cardiovascular disease; T2D, type 2 diabetes.