High-Protein Intake Impact on Human and Animal Kidney Function Across the Lifespan: Clinical Evidence and Emerging Concepts

Background/Objectives: High-protein diets have gained increasing popularity in recent years. This trend has raised concerns regarding its impact on renal function, particularly among individuals with chronic kidney disease (CKD). The aim of this narrative review is to summarize current evidence on the effect of high-protein intake on kidney function. An analysis across species and age groups takes into account both theoretical and clinical perspectives. Methods: A literature search was conducted in PubMed, Scopus, and Web of Science to identify experimental and animal studies, as well as data concerning adult and pediatric populations, with special focus on those with CKD. Results: Experimental studies confirm protein-triggered adaptive increase in intraglomerular pressure and subsequent hyperfiltration, yet without any long-term negative effect on a healthy kidney. Human adult studies indicate that high-protein dietary content may accelerate the progression of CKD. Conversely, in older individuals, high protein intake combined with plant-rich diet appears to protect against sarcopenia and is associated with increased longevity. In children with CKD, protein intake should be adjusted according to growth requirements. In both pediatric and general populations, increasing the proportion of plant-based protein relative to animal protein may improve the health outcomes, although evidence on kidney function protection is insufficient. Conclusions: A balance should be maintained between excessive protein intake, which may aggravate existing dysfunctions, and overly restrictive protein consumption, which may lead to sarcopenia in older adults and impaired growth/development in children. A personalized approach is essential, taking into account age, kidney function/CKD stage, comorbidities, and, in the pediatric population, growth rate and developmental needs.