Background: The human microbiota plays a crucial role in maintaining physiological homeostasis and influencing the development of chronic diseases not only in the gut but in the whole body. Material and Methods: This literature review is based on a comprehensive search of the PubMed database covering the period from 2008 to 2026. Approximately 65 key studies were included in the final analysis. Only articles published in English were included. The search included keywords such as microbiota, inflammaging, eubiosis, diet, gut diseases, cardiovascular diseases, diabetes, and osteoporosis. This narrative review explores the composition, development, and functional significance of the gut microbiota across the human lifespan, highlighting its dynamic interaction with environmental factors. Early-life microbial colonization, shaped by factors including delivery mode and breastfeeding, has long-term implications for immune system maturation and disease susceptibility. Results: A balanced gut microbiota (eubiosis) supports host health through metabolic activities, mainly by the production of short-chain fatty acids (SCFAs), which regulate intestinal barrier integrity, immune responses, and systemic inflammation. Contrarily, dysbiosis-characterized by reduced microbial diversity and an overrepresentation of pro-inflammatory species-is associated with chronic low-grade inflammation (inflammaging) and contributes to the pathogenesis of multiple diseases. Age-related changes in microbial composition are shown to activate inflammatory processes and impair immune regulation, thereby increasing disease risk. Therefore, it is important to recognize the role of microbiota alterations in key pathological conditions, including neurodegenerative diseases, cardiovascular diseases, type 2 diabetes mellitus, and osteoporosis. Conclusions: Finally, the potential of microbiome-targeted interventions, such as probiotics, prebiotics, and dietary modulation-in particular the Mediterranean diet is recognized as the most balanced-is discussed as a promising strategy to restore microbial balance and mitigate inflammaging. Further research is needed to better understand the association between microbiota and host health and to optimize therapeutic approaches for aging populations.
