The Effect of Protein Intake on Bone Disease, Kidney Disease, and Sarcopenia: A Systematic Review

Background: Protein is essential for optimal growth, function, and maintenance of health. Its impact on bone, kidney health, and sarcopenia progression remains debated. Objectives: This review examines the association between dietary protein intake and the risk of bone disease, kidney disease, and sarcopenia to inform protein dietary reference intake updates. Methods: We searched Medline, EMBASE, AGRICOLA, and Scopus from January 2000 to May 2024, supplemented by citation searching for relevant reviews and original research. We included randomized and nonrandomized controlled trials, prospective cohort studies, and nested case-control studies examining dietary protein intake without exercise. We assessed the risk of bias (RoB), performed a qualitative synthesis of low to moderate RoB studies, and evaluated the strength of evidence. Results: Of 82 articles detailing 81 unique studies, only 13 were assessed with low to moderate RoB and synthesized, comprising bone disease [4 randomized controlled trials (RCTs) and 1 prospective cohort study], kidney disease (1 RCT), and sarcopenia (9 RCTs). The overarching evidence was insufficient, largely due to the limited number of low to moderate RoB studies, the diversity of dietary protein interventions, and the broad range of outcomes, which complicated synthesis and comparison. Notably, sparse literature addressed children and adolescents, and only a single study each examined the impact of dietary protein intake on bone disease risk (yielding mixed findings) in these populations and on kidney disease risk (showing no significant effects) in adults. The findings on the impact of protein intake on bone disease in adults and sarcopenia risk were mixed; some studies showed no effect, whereas others indicated benefits. Conclusions: The evidence since 2000 on associations between dietary protein intake and the risks of bone disease, kidney disease, and sarcopenia is unclear, indicating a need for more rigorous research. This trial was registered at PROSPERO as CRD42023446621.