Associations of Dietary Protein Intake and Amino Acid Patterns with the Risk of Diabetic Kidney Disease in Adults with Type 2 Diabetes: A Cross-Sectional Study

Background/Objectives: Diabetic kidney disease (DKD) is a major complication of type 2 diabetes mellitus (T2DM), and recent research highlights that amino acid composition—rather than total protein intake alone—may influence DKD risk. This study aimed to evaluate the associations between dietary protein intake, specific amino acid profiles, and the risk of DKD among adults with T2DM. Methods: A total of 378 T2DM patients were enrolled in this cross-sectional study. Dietary intake was assessed via a 24 h recall and a validated semi-quantitative food frequency questionnaire. Nutrient analysis was based on the Taiwanese Food Composition Database. Participants were categorized into three protein intake groups: Group 1 (≤0.8 g/kg), Group 2 (0.9–1.2 g/kg), and Group 3 (≥1.3 g/kg). Cox proportional hazards models were used to evaluate the associations of crude protein, branched-chain amino acids to aromatic amino acids (BCAA/AAA) ratio, and ketogenic amino acid intake with DKD risk. Adjustments were made for age, sex, diabetes duration, and blood pressure. Results: While crude protein intake showed no significant association with DKD risk, higher intake of ketogenic amino acids (e.g., leucine and lysine) was consistently and significantly associated with reduced DKD risk (adjusted HR range = 0.698–0.716, p < 0.01). Our findings highlight the protective potential of ketogenic amino acids such as leucine and lysine, which were significantly associated with lower DKD risk. The BCAA/AAA ratio also showed a downward trend in DKD risk, though not statistically significant. Kaplan–Meier analysis revealed that moderate protein intake (0.9–1.2 g/kg) corresponded to the most favorable DKD-free survival. Conclusions: Our findings suggest that, beyond total protein quantity, the intake of ketogenic amino acids may play a protective role in DKD prevention. Moderate protein consumption combined with higher leucine and lysine intake appears beneficial. These results support incorporating amino acid profiling in dietary strategies for DKD risk reduction. Further longitudinal and interventional studies are recommended to validate these associations.