Association of dietary proteins with serum creatinine and estimated glomerular filtration rate in a general population sample: the CHRIS study

Background: Diet is known to affect kidney function. However, population-based studies provide contrasting evidence, resulting in a poor understanding of the effect of proteins from specific foods on kidney health. Methods: We analyzed the effect of total daily protein intake (TDPI) and source-specific daily protein intake (DPI) on fasting serum creatinine (SCr) and estimated glomerular filtration rate (eGFR) in the Cooperative Health Research In South Tyrol (CHRIS) cross-sectional study (n = 5889), using the GA²LEN food frequency questionnaire for TDPI and DPI estimation. We fitted multivariable adjusted mixed models of SCr and eGFR on TDPI and DPI quartiles (Q1-Q4) in the overall sample, and after removing individuals with known hypertension, diabetes or chronic kidney disease (CKD). Results: Higher TDPI as well as DPI from overall animal sources, fish, and poultry, were associated with higher SCr (trend test p, p_trend < 0.01), with larger effect after excluding individuals with known hypertension, diabetes or CKD. The eGFR was lower at higher TDPI (Q4 vs Q1: − 1.6 ml/min/1.73 m²; 95% CI − 2.5, − 0.7; p_trend = 3e−4) and DPI from fish (Q4 vs Q1: − 2.1 ml/min/1.73 m²; 95% CI − 2.9, − 1.20; p_trend = 4.3e−6), overall animal source (Q4 vs Q1: − 1.6 ml/min/1.73 m²; 95% CI −2.5, − 0.8), processed meat (Q4 vs Q1: − 1.4 ml/min/1.73 m²; p_trend = 0.027), red meat, offal and processed meat (Q4 vs Q1: − 1.4 ml/min/1.73 m²; p_trend = 0.015) and poultry (Q4 vs Q1: − 0.9 ml/min/1.73 m²; p_trend = 0.015). Conclusions: TDPI and DPI from specific animal sources were positively associated with SCr and negatively associated with eGFR. Lacking an alternative marker of kidney function, confounding involving muscle mass metabolism cannot be fully excluded. Graphical abstract: [Figure not available: see fulltext.]