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Background: The estimated glomerular filtration rate (eGFR), derived from serum creatinine (eGFRcr) or cystatin C (eGFRcys), is crucial for assessing kidney function and predicting health outcomes. While eGFRcr is known to be influenced by muscle mass and diet, eGFRcys is considered unaffected. This study aimed to identify lifestyle and anthropometric determinants of eGFRcys and eGFRcr in young, healthy men, and to explore the differential impact of these factors on the eGFR estimations.

Method: Cross-sectional study on 18 to 25.9-year-old healthy males. Participants completed questionnaires on diet and exercise, and underwent measurements of body composition and creatinine, cystatin C, and other serum analyses. eGFRcys was calculated using the CAPA equation, and eGFRcr using the LM-revised (LMR18) equation. Univariate and multivariate linear regressions were used to analyze associations between lifestyle or anthropometric variables and the eGFR's.

Results: No participants had an eGFR <60 ml/min/1.73 m2. We found novel positive correlations between eGFRcys and adherence to healthy eating guidelines according to a Healthy food habits score, and with serum B12, but a negative correlation with plasma homocysteine, in both univariate and multivariate analyses. In contrast, eGFRcr correlated negatively with fat-free mass, B12, and homocysteine in multivariate analysis, and with handgrip strength and hours of exercise in univariate analysis: it did not correlate with the Healthy food habits score.

Conclusions: Our findings highlight the differential impact of lifestyle and anthropometric factors on eGFRcys versus eGFRcr in young, healthy men. eGFRcys showed a significant association only with long-term dietary habits (Healthy food habits score and inversely with homocysteine), suggesting that eGFRcys may be more sensitive to lifestyle-related determinants of kidney function, whereas eGFRcr is more strongly influenced by non-renal factors such as muscle mass. Healthy food intake may positively affect kidney function in young healthy male subjects.