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Whole Grain, Bran, and Germ Intake and Risk of Type 2 Diabetes: A Prospective Cohort Study and Systematic Review

by Jeroen S. L. de Munter, Frank B. Hu, Donna Spiegelman, Mary Franz, Rob M. van Dam | 8/30/2007 8:51:19 AM

ABSTRACT Background Control of body weight by balancing energy intake and energy expenditure is of major importance for the prevention of type 2 diabetes, but the role of specific dietary factors in the etiology of type 2 diabetes is less well established. We evaluated intakes of whole grain, bran, and germ in relation to risk of type 2 diabetes in prospective cohort studies. Methods and Findings We followed 161,737 US women of the Nurses' Health Studies (NHSs) I and II, without history of diabetes, cardiovascular disease, or cancer at baseline. The age at baseline was 37–65 y for NHSI and 26–46 y for NHSII. Dietary intakes and potential confounders were assessed with regularly administered questionnaires. We documented 6,486 cases of type 2 diabetes during 12–18 y of follow-up. Other prospective cohort studies on whole grain intake and risk of type 2 diabetes were identified in searches of MEDLINE and EMBASE up to January 2007, and data were independently extracted by two reviewers. The median whole grain intake in the lowest and highest quintile of intake was, respectively, 3.7 and 31.2 g/d for NHSI and 6.2 and 39.9 g/d for NHSII. After adjustment for potential confounders, the relative risks (RRs) for the highest as compared with the lowest quintile of whole grain intake was 0.63 (95% confidence interval [CI] 0.57–0.69) for NHSI and 0.68 (95% CI 0.57–0.81) for NHSII (both: p-value, test for trend <0.001). After further adjustment for body mass index (BMI), these RRs were 0.75 (95% CI 0.68–0.83; p-value, test for trend <0.001) and 0.86 (95% CI 0.72–1.02; p-value, test for trend 0.03) respectively. Associations for bran intake were similar to those for total whole grain intake, whereas no significant association was observed for germ intake after adjustment for bran. Based on pooled data for six cohort studies including 286,125 participants and 10,944 cases of type 2 diabetes, a two-serving-per-day increment in whole grain consumption was associated with a 21% (95% CI 13%–28%) decrease in risk of type 2 diabetes after adjustment for potential confounders and BMI. Conclusions Whole grain intake is inversely associated with risk of type 2 diabetes, and this association is stronger for bran than for germ. Findings from prospective cohort studies consistently support increasing whole grain consumption for the prevention of type 2 diabetes. Jeroen S. L. de Munter(1,2), Frank B. Hu(1,3,4), Donna Spiegelman(3,5), Mary Franz(1), Rob M. van Dam(1,2,4*) 1 Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts, United States of America, 2 Institute of Health Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands, 3 Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, United States of America, 4 Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 5 Department of Biostatistics, Harvard School of Public Health, Boston, Massachusetts, United States of America Funding: This study was funded by research grants CA50385 and DK58845 from the National Institutes of Health. The study sponsors did not have any role in the study design; collection, analysis, and interpretation of data; writing of the paper; and decision to submit it for publication. Competing Interests: The authors have declared that no competing interests exist. Academic Editor: Leif C. Groop, Clinical Research Centre, Sweden Citation: de Munter JSL, Hu FB, Spiegelman D, Franz M, van Dam RM (2007) Whole Grain, Bran, and Germ Intake and Risk of Type 2 Diabetes: A Prospective Cohort Study and Systematic Review. PLoS Med 4(8): e261 doi:10.1371/journal.pmed.0040261 Received: March 20, 2007; Accepted: July 17, 2007; Published: August 28, 2007 Copyright: © 2007 de Munter et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Abbreviations: BMI, body mass index; CI, confidence interval; FFQ, food frequency questionnaire; NHS, Nurses' Health Study; RR, relative risk * To whom correspondence should be addressed. E-mail: [email protected]


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