The human gut microbiome represents a sophisticated ecosystem in which different clusters called ‘guilds’ and peculiar properties develop from intricate local microbial interactions. This review evaluates how environmental factors, climate change, and lifestyle choices remodel microbial connectivity and health. The MANOCCA (Multivariate Analysis of Conditional Covariance Analysis) framework indicates that advancing age and smoking disrupt microbial networks, whereas elevated BMI (Body Mass Index) is associated with increased network densification. A primary mechanism of host protection is colonization resistance against ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens, maintained through nutritional competition and the production of metabolites like short-chain fatty acids (SCFAs) and bacteriocins. Environmental stressors, including climate change, exacerbate dysbiosis and thermal stress, which compromises the intestinal barrier. Anthropogenic pollutants, specifically pesticides and micro/nanoplastics (MNPs), act as biological reservoirs for toxins, triggering oxidative stress, NF-κB-mediated inflammation, and “leaky gut” syndrome. Dietary patterns also play a fundamental role; while ultra-processed foods deplete microbial diversity, the Mediterranean diet and bioactive compounds promote eubiosis. Additionally, the microbiota modulates host responses to ionizing radiation, facilitating tissue repair. Integrating multi-omics and precision medicine is essential to improve targeted therapies, such as engineered probiotics, to reestablish homeostasis in a changing environment.