Impact of Dietary Protein Intake on Gut Microbiota: A Narrative Review of Biological Effects and Clinical Relevance

Protein intake is essential for maintaining physiological functions, with standard recommendations suggesting ∼0.7 g/kg/day for healthy adults. In recent years, high-protein diets have gained popularity due to their potential metabolic benefits, including reduced visceral adiposity, improved hormonal regulation, and preservation of muscle mass. However, the effects of high-protein intake on gut microbiota and overall health remain controversial. Emerging evidence indicates that excessive protein consumption, particularly from animal sources, may negatively impact gut health by increasing intestinal permeability, promoting chronic low-grade inflammation, and impairing mucosal immunity. These effects appear to depend on protein source, intake level, duration, and host-specific factors such as age, metabolic status, and immune function. While moderate protein intake seems to have minimal effects on microbial diversity, chronic high intake may disrupt gut microbiota composition and favor pro-inflammatory profiles, potentially contributing to metabolic dysfunction. Additionally, co-ingested dietary factors, including fat content, processed meat compounds, and fiber intake, may confound these outcomes. Certain populations, such as athletes, older adults, and individuals with type 2 diabetes, may benefit from higher protein intake, although these effects are context-dependent. In contrast, high-protein diets may be detrimental for individuals at risk of chronic kidney disease. Overall, the gut microbiota plays a central role in mediating the health effects of dietary protein, highlighting the importance of balanced and personalized nutritional strategies.