Higher Whole-Grain Intake Associated With Increased Insulin Sensitivity

Mindy Hung

November 07, 2003

Nov. 7, 2003 — Higher whole-grain intake is associated with increased insulin sensitivity (S I), according to a study published in the November issue of the American Journal of Clinical Nutrition.

"To our knowledge, no population-based data exist on the effect of whole grains on a direct measure of insulin sensitivity," write Angela D. Liese, PhD, MPH, and colleagues from the Arnold School of Public Health at the University of South Carolina, Columbia, and colleagues

Investigators evaluated data from the Insulin Resistance Atherosclerosis Study (IRAS), a multicenter study that attempted to draw nearly equal representation of participants across categories of glucose tolerance status (44.2% had normal glucose tolerance, 22.7% had impaired glucose tolerance, and 33.1% had type 2 diabetes), ethnicity (38% were non-Hispanic white, 34% were Hispanic, and 29% were African American), sex, and age.

Dr. Liese and colleagues limited their analysis to IRAS subjects with normal or impaired glucose tolerance. They also excluded participants with missing or error-laden data, and insulin sensitivity, leaving 978 participants with complete data for analysis.

Before each of the two visits required by IRAS protocol, participants in the study fasted for 12 hours, abstained from alcohol and strenuous exercise for 24 hours, and refrained from smoking the morning of the test. During the first visit, investigators performed an oral glucose tolerance test. During the second visit, they used the frequently sampled intravenous glucose tolerance test to measure S I.

Investigators conducted a one-year activity recall physical activity assessment. They also interviewed participants using a one-year, semiquantitative 114-item food frequency questionnaire (FFQ) modified from the National Cancer Institute Health History and Habits Questionnaire.

The FFQ included inquiries on whether serving sizes were "small, medium, or large compared with other men or women about your age" and on consumption of dark bread, high-fiber cold cereals, and cooked cereals.

Investigators used multivariable linear regression to model the relation of whole-grain intake to log(S I + 1) and to log(insulin).

IRAS participants consumed on average 0.8 servings daily of whole grain-containing foods, mostly in the form of dark breads. Subjects' mean intake of whole grain did not differ significantly across categories. Increased intake of whole grains was significantly associated with S I after adjustment for demographics, total energy intake and expenditure, smoking, and family history of diabetes (β = 0.082; P = .005) and insulin (β = -0.0646; P = .019).

Adjustment for body mass index and waist circumference attenuated but did not explain the association with S I. Analysis of nutritional components also found that the presence of fiber and magnesium in whole grain products might explain a significant amount of the association to S I, because both products were associated with insulin sensitivity (β magnesium(mg/d) = 0.00013; P = .0469; β fiber (g/d) = 0.011; P = .0151).

Dr. Liese and colleagues acknowledge that the broad categories of the FFQ limited subjects' ability to report consumption of other whole grain foods such as whole-grain pasta or brown rice.

"Given that insulin sensitivity is one of the main predictors of diabetes, our findings support previous reports on the protective effects of whole grains on the risk of developing diabetes in men and women by substantiating one of the underlying mechanisms," the investigators write.

Am J Clin Nutr. 2003;78:985-971

Reviewed by Gary D. Vogin, MD

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