Human Gut Microbiome

The human gut microbiome is the ecological system formed by microorganisms living in the digestive tract, together with their genes and products. Its organisms, collectively called the gut microbiota, interact with food and host tissues to support nutrition, metabolism, defence and physiological signalling.

Digestion and nutrient metabolism

Gut microorganisms process dietary components that human enzymes cannot fully digest, especially complex carbohydrates and fibre.

• Microbial fermentation produces short-chain fatty acids, chiefly acetate, propionate and butyrate, which supply energy to intestinal cells and participate in host metabolic regulation.
• The microbiota synthesizes some vitamins, including vitamin K and certain B vitamins, although their contribution to host requirements varies.
• Microbial enzymes modify bile acids and other food-derived compounds, influencing their absorption and metabolic effects.

Protection and immune regulation

The microbiota works with the intestinal lining to maintain a balanced relationship between the body, food antigens and microorganisms.

• Resident microbes provide colonisation resistance by competing with pathogens for nutrients and attachment sites and by producing inhibitory substances.
• Microbial signals help develop and regulate the mucosal immune system, including immune tolerance and appropriate inflammatory responses.
• Microbial metabolites support the mucus layer, epithelial cells and intercellular junctions that form the intestinal barrier.

Communication with other organs

The gut microbiome functions as part of a wider signalling network rather than as an isolated digestive community.

• Microbial metabolites can enter host circulation and influence energy homeostasis, glucose and lipid metabolism.
• Gut microbes interact with neural, endocrine and immune pathways within the gut-brain axis, thereby influencing intestinal motility, appetite-related signalling and nervous-system functions.
• The microbiome also transforms some medicines and foreign compounds, potentially altering their activity or availability.