Microbiome: Friend or Friendly Foe.

The human microbiome is a dynamic, polymicrobial ecosystem that plays an essential role in nutrition, immune development, barrier integrity, and host physiology, acting as a mutualistic partner under balanced conditions. However, its ecological complexity, genetic adaptability through horizontal gene transfer, and interactions with other prokaryotes as well as protozoan and metazoan parasites can transform commensals into pathobionts, resulting in weakened host's barriers, immunity declines with the progression of age, and community composition shifts toward dysbiosis. Factors such as diet, genetics, aging, immune-senescence, impaired autophagy, and environmental exposure, all influence this delicate balance, determining whether the microbiome remains protective or becomes an opportunistic source of inflammation and disease. This review focuses on the study of the intestinal microbiome in humans. Maintaining microbiome homeostasis is promoted through (a) dietary diversity, (b) limited antimicrobial use, (c) use of probiotics, (d) support for gut barrier function, and (e) healthy lifestyle improvements. These actions and considerations are critical to prevent the emergence of pathogenic states and preserving the microbiome's vital role in host health throughout life.