Effects of 12 weeks of resistance and concurrent training with graded protein intakes on lipid profile, kidney and liver biomarkers in middle-aged to older women

Purpose This study examined whether dietary protein dose modifies adaptations to resistance training (RT) versus concurrent training (CT) in middle-aged to older women, focusing on lipid profile and kidney and liver biomarkers. Methods A total of 108 middle-aged to older women (40–77 years) were randomized to 12 weeks of supervised RT or CT (3 sessions/week), combined with low (0.8 g·kg⁻¹·d⁻¹), moderate (1.6 g·kg⁻¹·d⁻¹), or high (2.2 g·kg⁻¹·d⁻¹) protein intake (six groups; n = 18/group). Only participants with complete pre-post data were included; the analyzed sample comprised n = 83 (CT1 n = 14, CT2 n = 15, CT3 n = 13, RT1 n = 13, RT2 n = 14, RT3 n = 14). Results TG, TC, LDL-C and ApoB decreased and HDL-C increased from pre to post (p FDR ≤ 0.05). These improvements were generally greater at 1.6 and/or 2.2 vs 0.8 g·kg⁻¹·d⁻¹ (Time × Protein, p FDR ≤ 0.05), and for several lipids the protein-related benefit differed by training mode (Time × Training × Protein, p FDR ≤ 0.05; primarily at 1.6 g·kg⁻¹·d⁻¹). Urea and BUN increased pre to post, with dose-dependent elevations at 1.6 and 2.2 vs 0.8 (Time × Protein, p FDR < 0.001), accompanied by small creatinine/cystatin C increases and modest eGFR reductions at higher protein intakes (p FDR ≤ 0.05). ALT, AST and GGT increased from pre to post with clear protein-dose effects (Time × Protein, p FDR < 0.001), and AST/GGT showed training-dependent protein responses (Time × Training × Protein, p FDR ≤ 0.05). For TG, the overall decrease was attenuated in RT relative to CT. Conclusions Twelve weeks of supervised RT or CT combined with controlled protein intakes elicited favorable lipid changes overall, while higher protein doses (particularly 1.6–2.2 g·kg⁻¹·d⁻¹) were associated with greater improvements in selected lipid outcomes but also with dose-dependent increases in urea/BUN and modest reductions in eGFR estimates, and increases in liver enzymes, some of which differed by training modality. These findings indicate that protein dose meaningfully modifies metabolic and clinical chemistry responses to training in middle-aged to older women, and that higher protein intake may involve trade-offs between lipid benefits and changes in kidney- and liver-related biomarkers.