Dietary protein intake in relation to metabolic syndrome reversion: findings from the Tehran lipid and glucose study

Dietary protein quantity and quality may influence metabolic regulation and cardio-metabolic outcomes, yet little is known about their role in metabolic syndrome (MetS) reversion, a beneficial transition linked to reduced disease risk. This study examined associations between total and source-specific dietary protein intake and MetS reversion in Iranian adults. Adults with MetS at baseline (Phase 3, 2006-2008) of the Tehran Lipid and Glucose Study were followed until Phase 6. Dietary intake was assessed using a validated 168-item food frequency questionnaire. Total, animal and plant-based protein, as well as protein food-specific sources (red meat, processed meat, poultry, dairy, legumes, and nuts) was categorized into tertiles. MetS reversion was defined as the transition from MetS to non-MetS during follow-up, categorized by timing: final phase, any phase, early, and sustained reversion. Cox proportional hazards regression models estimated hazard ratios (HRs) and 95% confidence intervals (CIs), adjusted for covariates. In the fully adjusted models, participants in the second tertile of animal protein intake had a significant lower HR for "any phase MetS reversion" (HR: 0.68; 95% CI: 0.48-0.96), compared to the participants in the first tertile. Also, participants in the second tertile of poultry intake had higher HRs for "any phase MetS reversion" (HR: 1.47; 95% CI: 1.03-2.09) and "early phase MetS reversion" (HR: 1.58; 95% CI: 1.01-2.46), compared to the participants in the first tertile. Furthermore, higher intakes of dairy products and nuts were associated with 48% (HR: 0.52; 95% CI: 0.31-0.86) and 43% (HR: 0.57; 95% CI: 0.35-0.92) lower HRs for "early phase MetS reversion", respectively. No significant associations were observed between dietary protein sources and sustained MetS reversion; however, the small number of sustained reversion events (n = 31, 5.4%) limited statistical power for this outcome, precluding definitive conclusions about long-term metabolic maintenance.