The association between dietary carbohydrate to protein ratio and risk of cardiovascular disease, type 2 diabetes, and metabolic syndrome in Iranian adults: a cohort study

BACKGROUND: The dietary balance of macronutrients may play a critical role in the development of cardio-metabolic diseases. The carbohydrate-to-protein (CHO/Pr) ratio provides an index of this balance; however, its association with long-term health outcomes in Middle Eastern populations remains unclear. We investigated the relationship between dietary CHO/Pr ratio and the incidence of cardiovascular disease (CVD), type 2 diabetes mellitus (T2DM), and metabolic syndrome (MetS) among adults from the Tehran Lipid and Glucose Study (TLGS). METHODS: A total of 2648 adults free of CVD, 2256 adults free of T2DM, and 1713 adults free of MetS at baseline (2006-2008) were included. Dietary intakes were assessed using a validated 168-item food frequency questionnaire. The CHO/Pr ratio was calculated and categorized into tertiles. Hazard ratios (HRs) and 95% confidence intervals (CIs) for incident cardio-metabolic outcomes were estimated using Cox proportional hazards regression, adjusted for demographic, lifestyle, and dietary covariates. RESULTS: Over median follow-up periods of 10.6, 8.5, and 7.6 years for CVD, T2DM, and MetS, respectively, 171 CVD, 241 T2DM, and 596 MetS cases occurred. Compared with the lowest tertile, participants in the second tertile of CHO/Pr ratio had a higher risk of CVD (HR = 1.48; 95% CI: 1.01-2.17), whereas no significant association was observed in the highest tertile. No significant associations were found between CHO/Pr ratio and incidence of T2DM or MetS. CONCLUSIONS: A moderate CHO/Pr ratio was associated with an increased risk of CVD, but not with T2DM or MetS. These findings highlight the potential importance of macronutrient balance in cardiovascular prevention.