Purpose of Review <p>It is now evident that the microorganisms living on and inside the human body modulate a myriad of host responses and activities. Particularly, the intestinal microbiota, which comprises diverse bacteria, fungi, archaea, viruses, and eukaryotic entities, forms a close relationship with the host. This relationship is essential for optimal biological function such as maintaining proper immune homeostasis, host metabolism, and prevention of pathogens colonization. The human gut microbiome is relatively stable after 3 years of age but is subjected to influences from diet, environment and lifestyle factors. This review covers recent findings on how lifestyle factors associated with modern society might affect the microbiome.</p> Recent Findings <p>Modern lifestyle factors including circadian rhythm disruption, sleep deprivation, exercise and stress impact the gut bacterial community (bacteriome) composition and function. The resultant gut bacteriome changes contribute to host metabolism dysregulation, inflammatory diseases and cancer development associated with these lifestyle factors.</p> Summary <p>Lifestyle factors influence the gut bacteriome to modulate host health and disease risks. Understanding the mechanistic roles of diverse host-associated microorganisms played in lifestyle factors-associated disease risks holds the promise for developing novel approaches to alleviate the detrimental effects.</p>