Gut microbiota includes a vast collection of microorganisms
residing
within the gastrointestinal tract. It is broadly recognized that the
gut and brain are in constant bidirectional communication, of which
gut microbiota and its metabolic production are a major component,
and form the so-called gut microbiome–brain axis. Disturbances
of microbiota homeostasis caused by imbalance in their functional
composition and metabolic activities, known as dysbiosis, cause dysregulation
of these pathways and trigger changes in the blood–brain barrier
permeability, thereby causing pathological malfunctions, including
neurological and functional gastrointestinal disorders. In turn, the
brain can affect the structure and function of gut microbiota through
the autonomic nervous system by regulating gut motility, intestinal
transit and secretion, and gut permeability. Here, we examine data
from the CAS Content Collection, the largest collection of published
scientific information, and analyze the publication landscape of recent
research. We review the advances in knowledge related to the human
gut microbiome, its complexity and functionality, its communication
with the central nervous system, and the effect of the gut microbiome–brain
axis on mental and gut health. We discuss correlations between gut
microbiota composition and various diseases, specifically gastrointestinal
and mental disorders. We also explore gut microbiota metabolites with
regard to their impact on the brain and gut function and associated
diseases. Finally, we assess clinical applications of gut-microbiota-related
substances and metabolites with their development pipelines. We hope
this review can serve as a useful resource in understanding the current
knowledge on this emerging field in an effort to further solving of
the remaining challenges and fulfilling its potential.