Optimal measures of carbohydrate quality to lower the risk of type 2 diabetes: findings from 3 prospective cohort studies

BACKGROUND: Numerous carbohydrate quality metrics (CQMs) have been suggested, yet the optimal one(s) associated with the lowest type 2 diabetes (T2D) risk remains unknown. OBJECTIVES: We aimed to systematically compare 23 CQMs with T2D risk, identify the 5 strongest associations, propose an alternate Carbohydrate Quality Index (aCQI), and compare it with the existing CQI regarding T2D risk and cardiometabolic biomarkers. METHODS: We included participants of 3 prospective cohort studies [Nurses' Health Study I (1984-2020) and II (1991-2019), and Health Professionals Follow-up Study (1986-2020)], who were free of cancer, diabetes, and cardiovascular disease. Our primary outcome was incident T2D. We examined 13 plasma biomarkers in relation to CQIs among a subset. RESULTS: During 5,628,955 person-years of follow-up among 213,704 adults, 22,351 cases of incident T2D were ascertained. In multivariable-adjusted models, comparing Q5 to Q1, intakes of cereal fiber [relative risk (RR): 0.77 (0.74-0.81)], whole-fruit carbohydrates [RR: 0.80 (0.76-0.84)], glycemic index [RR: 1.20 (1.14-1.26)], sugar from sugar-sweetened beverages [RR: 1.22 (1.17-1.28)], and whole-grain carbohydrates [RR: 0.86 (0.82-0.91)] had the strongest associations with T2D risk. The aCQI [RR: 0.71 (0.68-0.75)], comprising these variables, had a larger magnitude of association with T2D risk than the original CQI [RR: 0.82 (0.79-0.87)], which included total fiber intake, glycemic index, the ratios of whole to total grains, and solid to total carbohydrates. The aCQI had significant associations with a larger percentage of differences in cardiometabolic biomarker concentrations, such as C-peptide, leptin, and LDL cholesterol, than the CQI (all P-trend ≤ 0.001). CONCLUSIONS: The novel aCQI, comprised carbohydrates from whole fruits, whole grains, sugar-sweetened beverages, cereal fiber, and glycemic index, was more strongly associated with risk of T2D and cardiometabolic biomarkers than its individual components or the existing CQI, necessitating further research.