Discuss the role of the gastrointestinal microbiota in human health and disease

Discuss the role of the gastrointestinal microbiota in human health and disease, including its impact on digestion, nutrient absorption, immune function, and metabolic homeostasis. How do symbiotic bacteria in the gut microbiome ferment dietary fibers, produce vitamins, and metabolize xenobiotics, contributing to host nutrition and energy metabolism? Moreover, how does dysbiosis of the gut microbiota, characterized by alterations in microbial composition and diversity, contribute to the pathogenesis of conditions like inflammatory bowel disease, obesity, and metabolic syndrome?