Background: Studies of whole grain and chronic disease have often included bran-enriched foods and other ingredients that do not meet the current definition of whole grains. Therefore, we assessed the literature to test whether whole grains alone had benefits on these diseases.

Objective: The objective was to assess the contribution of bran or cereal fiber on the impact of whole grains on the risk of type 2 diabetes (T2D), obesity and body weight measures, and cardiovascular disease (CVD) in human studies as the basis for establishing an American Society for Nutrition (ASN) position on this subject.

Design: We performed a comprehensive PubMed search of human studies published from 1965 to December 2010.

Results: Most whole-grain studies included mixtures of whole grains and foods with ≥25% bran. Prospective studies consistently showed a reduced risk of T2D with high intakes of cereal fiber or mixtures of whole grains and bran. For body weight, a limited number of prospective studies on cereal fiber and whole grains reported small but significant reductions in weight gain. For CVD, studies found reduced risk with high intakes of cereal fiber or mixtures of whole grains and bran.

Conclusions: The ASN position, based on the current state of the science, is that consumption of foods rich in cereal fiber or mixtures of whole grains and bran is modestly associated with a reduced risk of obesity, T2D, and CVD. The data for whole grains alone are limited primarily because of varying definitions among epidemiologic studies of what, and how much, was included in that food category.