In resistance-trained men, 16 weeks of high protein intake (3.2 g·kg⁻¹·d⁻¹) did not produce statistically detectable differences in renal biomarker or eGFR changes compared with moderate protein intake (1.6 g·kg⁻¹·d⁻¹), irrespective of training modality, though the limited sample size precludes excluding clinically meaningful differences.
Key Findings
Results
No statistically significant Time × Protein or Time × Training × Protein interactions were detected for any renal biomarker or eGFR estimate.
All interaction p-values were ≥ 0.182.
Linear mixed-effects models (Time × Training × Protein) were used to assess factorial effects.
Outcomes included BUN, BUN/creatinine ratio, cystatin C, and eGFR from the CKD-EPI creatinine (2021), cystatin C (2012), and creatinine-cystatin C (2021) equations.
Forty-four of 48 randomized resistance-trained men with complete pre- and post-data were analyzed.
Results
The 1.6 g·kg⁻¹·d⁻¹ protein groups showed no significant within-group changes in renal biomarkers or eGFR after 16 weeks.
All within-group paired t-test p-values were > 0.05.
This applied to both the resistance training and concurrent training groups.
Results
In both 3.2 g·kg⁻¹·d⁻¹ groups (RT and CT), BUN and cystatin C increased within groups.
All p-values were ≤ 0.017 by paired t-tests.
The increases were described as modest.
The authors state these within-group findings were descriptive because the corresponding interaction effects were not statistically significant.
Results
In both 3.2 g·kg⁻¹·d⁻¹ groups, eGFR estimates decreased within groups across the equations used.
All p-values were ≤ 0.009.
Decreases were described as small.
Equations were CKD-EPI creatinine (2021), cystatin C (2012), and creatinine-cystatin C (2021).
These changes were not supported by significant factorial interactions.
Results
The BUN/creatinine ratio remained unchanged in the high-protein groups.
p ≥ 0.614 for within-group changes.
Conclusions
The authors conclude that high protein did not produce detectable differences in renal outcomes versus moderate protein regardless of training modality, but the study was underpowered to exclude clinically meaningful differences.
Design: 2 × 2 factorial randomization of 48 men (26 ± 6 years; BMI 25.6 ± 2.9 kg·m⁻²) to RT or CT (4 sessions/week) with 1.6 or 3.2 g·kg⁻¹·d⁻¹ protein for 16 weeks.
Authors note the limited sample size and call for larger studies.
What This Means
This study looked at whether eating a very high-protein diet (about twice the commonly recommended amount for athletes, 3.2 g per kg of body weight daily) for 16 weeks affects kidney-related blood markers in healthy, resistance-trained men. Forty-eight men were assigned to either weight training or weight training plus endurance training, and to either a moderate (1.6 g/kg) or high (3.2 g/kg) protein intake. Forty-four had complete data for analysis.
When comparing the high- and moderate-protein groups directly, the researchers found no statistically significant differences in changes in kidney markers (BUN, cystatin C, and estimated kidney filtration rate), and this was true for both training types. Within the high-protein groups alone, BUN and cystatin C rose modestly and estimated filtration rate fell slightly, but the moderate-protein groups showed no changes. Because the direct comparisons were not significant, the authors treat these within-group changes as descriptive only.
This research suggests that, in healthy resistance-trained men, 16 weeks of high protein intake did not clearly differ from moderate intake in effects on these kidney markers. However, the study was small, so it cannot rule out meaningful differences, and it did not examine longer periods or people with existing kidney problems. Larger studies are needed to confirm these findings.
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Bagheri R, Karimi Z, Ghobadi H, Kazeminasab F, Kreider R, Ferns G, et al.. (2026). Exploratory serum renal biomarker and eGFR responses to high-protein diets during resistance versus concurrent training in resistance-trained men.. Journal of the International Society of Sports Nutrition. https://doi.org/10.1080/15502783.2026.2757309