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A whole (grain) in the evidence

Whole grain is thought to be heart healthy, mainly because of observational evidence. Are randomized controlled trials consistent with this recommendation?

Study under review: Whole grain cereals for the primary or secondary prevention of cardiovascular disease

Introduction

Whole grains are touted as the definitively healthier choice when compared to refined grains. The U.S. Dietary Guidelines advise people to get 50% of their grains from whole grain sources as part of a healthy diet. Eating whole grains has been associated with weight management[1], prevention of diabetes[2], and improved heart health[3]. As shown in Figure 1, it’s also been associated with mortality. In fact, the FDA approved some food packaging health claims stating an association between whole grain intake and better cardiovascular health. The idea that whole grains are heart healthy is repeated so frequently that it seems intuitive.

Whole grains have healthful components shown to have an effect on surrogate markers for heart disease, including viscous fiber[4] such as β-glucans, which is found in oats and barley and lowers[5] serum LDL levels by increasing fecal excretion of bile acids[6]. The fiber also possibly contributes to the positive effect of whole grains on glycemic control, though the evidence on this is mixed.

However, advice to increase whole grain intake for heart health stems not from biochemical, but epidemiological research, which shows whole grain intake associated with lower heart disease risk. While epidemiology is important to the study of nutrition, randomized controlled trials (RCTs) in humans are needed to establish a causal link between increased whole grain intake and protection from cardiovascular disease.

In the study examined here, authors pooled data from all qualifying RCTs testing the effects of whole grains on cardiovascular disease or cardiovascular disease risk markers. Their goal, as part of a Cochrane review, was to assess the quality and quantity of experimental evidence that exists on this issue.

Whole grains are widely believed to be beneficial to health, particularly cardiovascular health. Most advice recommending high intakes of whole grains is based on epidemiological evidence, which links higher intake of whole grains with lower rates of cardiovascular disease. There is less experimental evidence to back up health claims for whole grains, however. In the study examined here, authors conducted a meta-analysis on existing experimental data looking at whole grain intake and heart disease.

Who and what was studied?

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Other Articles in Issue #37 (November 2017)