Dietary carbohydrate intake and risk of type 2 diabetes: a 16-year prospective cohort study

Despite considerable research underscoring the importance of carbohydrate intake in relation to the risk of type 2 diabetes (T2D), a comprehensive assessment of this relationship is currently lacking. We aimed to examine the associations of various types and food sources of dietary carbohydrate intake with the risk of T2D, to evaluate potential effect modification by other factors, including genetic susceptibility, and to explore the potential mediators for such associations. The present study included 161,872 participants of the UK Biobank who were free of prevalent cancer, cardiovascular disease, or diabetes, and had at least one validated 24-h dietary recall assessment. Multivariable-adjusted age-stratified Cox proportional hazard regression models were applied to estimate hazard ratios (HRs) and 95% confidence intervals (CI) for the associations of various types and food sources of dietary carbohydrate intake with risk of T2D. During a median follow-up of 13.6 years, 4,176 incident cases of T2D were identified. In the multivariable-adjusted models, a greater intake of fiber, carbohydrates from whole grains, and carbohydrates from non-starchy vegetables was significantly associated with a lower risk of T2D (highest vs. lowest quantile, HR [95% CI]=0.70 [0.62-0.79], 0.74 [0.67-0.82], and 0.83 [0.75-0.92], respectively, all P for trend <0.005). In contrast, a higher intake of starch and carbohydrate from starchy vegetables was associated with an increased risk of T2D (highest vs. lowest quantile, HR [95% CI]=1.31 [1.16-1.48] and 1.19 [1.09-1.31], respectively, both P for trend <0.005). Replacing one serving of refined grains or starchy vegetables with an equal amount of whole grains or non-starchy vegetables was associated with 4% to 10% lower risk of T2D (all P values <0.001). The observed associations were generally similar across population subgroups, including individuals with different genetic susceptibility to T2D. Mediation analyses of the inverse association between T2D risk and isocaloric substitution of carbohydrates from refined grains with carbohydrate from whole grains demonstrated that 39.6%, 43.4%, 44.0%, 27.8%, and 34.9% were mediated through body mass index, waist-to-hip ratio, glycosylated hemoglobin, high-density lipoprotein cholesterol, and C-reactive protein, respectively. In addition, the inverse association between the isocaloric substitution of carbohydrates from starchy vegetables with carbohydrates from non-starchy vegetables and T2D was partially mediated through high-density lipoprotein cholesterol (15.9%). These findings underscore the importance of dietary modifications of carbohydrates, particularly considering types and food sources of carbohydrate intake, in the primary prevention of T2D.