Longitudinal Association Between Carbohydrate Quality and Impaired Fasting Glucose in Chinese Older Adults: A Case-Control Study

Background: Most studies have focued on carbohydrate quantity in glycemic regulation, while evidence linking carbohydrate quality to impaired fasting glucose (IFG), particularly among community-dwelling older adults in northern China, remains scarce. The carbohydrate quality index (CQI) is an integrated indicator that incorporates dietary fiber, whole-grain proportion, glycemic index (GI), and carbohydrate food sources to evaluate overall carbohydrate quality. This 1:2 individually age- (±2 years) and sex-matched case–control study within the Tianjin Elderly Nutrition and Cognition (TENC) cohort was conducted to examine the association between CQI and incident IFG in older adults in northern China and to provide evidence for carbohydrate-targeted dietary guidance to maintain glycemic health. Methods: Participants were recruited from the TENC prospective cohort (Clinical Trial Registration: ChiCTR2000034348), with a baseline population of 5918 adults aged ≥60 years. After sequential baseline and follow-up exclusions, 149 cases with newly onset IFG were individually matched to 298 normoglycemic controls, forming a final analytical sample of 447 participants. Dietary CQI, calculated from food frequency questionnaire (FFQ) data, served as the exposure, and incident IFG (6.1 mmol/L ≤ fasting blood glucose (FBG) < 7.0 mmol/L) was defined as the study outcome. Results: The total sample had a mean age of 68.15 ± 4.37 years, with 49% female participants. Matching covariates (age and sex) were balanced between groups, and no intergroup differences were observed in body mass index (BMI) (p > 0.05). Controls exhibited significantly higher CQI scores than cases (p = 0.002). Compared with IFG cases, controls consumed more whole grains, fruits, eggs, and dietary fiber, had lower dietary GI levels, and reported less alcohol consumption (all p < 0.05). After adjustment for potential confounders, including marital status, BMI, smoking, alcohol consumption, physical activity, and total energy intake, CQI was independently and inversely associated with incident IFG. Relative to participants in the lowest CQI quartile (Q1), those in the highest quartile (Q4) had a 76.3% lower IFG risk (odds ratio (OR) = 0.237, 95% confidence interval (CI): 0.097–0.579). Conclusion: Higher CQI is independently associated with the risk of incident IFG among community-dwelling older adults in northern China. Hence, optimizing the quality of dietary carbohydrates may be as a feasible nutritional strategy to mitigate glycemic dysregulation and prevent IFG in older populations.