Carbohydrate quality and quantity and risk of type 2 diabetes in US women

Abstract

Background: Carbohydrate quality may be an important determinant of type 2 diabetes (T2D); however, relations between various carbohydrate quality metrics and T2D risk have not been systematically investigated.

Objective: The purpose of this study was to prospectively examine the association between carbohydrates, starch, fibers, and different combinations of these nutrients and risk of T2D in women.

Design: We prospectively followed 70,025 women free of cardiovascular disease, cancer, and diabetes at baseline from the Nurses' Health Study (1984-2008). Diet information was collected with the use of a validated questionnaire every 4 y. Cox regression was used to evaluate associations with incident T2D.

Results: During 1,484,213 person-years of follow-up, we ascertained 6934 incident T2D cases. In multivariable analyses, when extreme quintiles were compared, higher carbohydrate intake was not associated with T2D (RR = 0.98; 95% CI: 0.89, 1.08; P-trend = 0.84), whereas starch was associated with a higher risk (RR = 1.23; 95% CI: 1.12, 1.35; P-trend <0.0001). Total fiber (RR = 0.80; 95% CI: 0.72, 0.89; P-trend < 0.0001), cereal fiber (RR = 0.71, 95% CI: 0.65, 0.78; P-trend < 0.0001), and fruit fiber (RR = 0.79; 95% CI: 0.72, 0.85; P-trend < 0.0001) were associated with a lower T2D risk. The ratio of carbohydrate to total fiber intake was marginally associated with a higher risk of T2D (RR = 1.09; 95% CI: 1.00, 1.20; P-trend = 0.04). On the other hand, we found positive associations between the ratios of carbohydrate to cereal fiber (RR = 1.28; 95% CI: 1.17, 1.39; P-trend < 0.0001), starch to total fiber (RR = 1.12; 95% CI: 1.02, 1.23; P-trend = 0.03), and starch to cereal fiber (RR = 1.39; 95% CI: 1.27, 1.53; P-trend < 0.0001) and T2D.

Conclusions: Diets with high starch, low fiber, and a high starch-to-cereal fiber ratio were associated with a higher risk of T2D. The starch-to-cereal fiber ratio of the diet may be a novel metric for assessing carbohydrate quality in relation to T2D.

Keywords: carbohydrate quality; carbohydrate-to-fiber ratio; fiber; starch; type 2 diabetes.

FIGURE 1

RR of T2D by joint effect analysis of carbohydrate or starch and total or cereal fiber intake (cases = 6934, person-years = 1,484,213). Adjusted RR of T2D according to joint classifications of carbohydrates and total fiber (A), carbohydrates and cereal fiber (B), starch and total fiber (C), and starch and cereal fiber (D). The analysis was adjusted for age, BMI, family history of diabetes, postmenopausal status, smoking status, alcohol intake, physical activity level, multivitamin use, race, total energy intake, red meat, coffee, magnesium, ratio of polyunsaturated fat to saturated fat, and trans fat. Panel C is additionally adjusted for sugar-sweetened beverages. Panel D is additionally adjusted for sugar-sweetened beverages and fruit and vegetable fiber. RRs were calculated with the use of the Cox proportional hazards regression model. P values for interactions are presented below. T2D, type 2 diabetes.

FIGURE 2

RR of T2D by starch (A) and starch-to–cereal fiber (B) intake with the use of restricted cubic spline regression. (A) P-nonlinear relation = 0.44, and P-linear relation < 0.0001. (B) P-nonlinear relation = 0.01, and P-overall significance of the curve < 0.0001. The analysis was adjusted for age, BMI, family history of diabetes, postmenopausal status, smoking status, alcohol intake, physical activity level, multivitamin use, race, total energy intake, red meat, coffee, magnesium, ratio of polyunsaturated fat to saturated fat, and trans fat. The model for starch was additionally adjusted for cereal fiber, sugar-sweetened beverages, and fruits and vegetables. The starch-to–cereal fiber model was additionally adjusted for sugar-sweetened beverages and fruit and vegetable fiber. T2D, type 2 diabetes.