'Gut health': a new objective in medicine?

Abstract

'Gut health' is a term increasingly used in the medical literature and by the food industry. It covers multiple positive aspects of the gastrointestinal (GI) tract, such as the effective digestion and absorption of food, the absence of GI illness, normal and stable intestinal microbiota, effective immune status and a state of well-being. From a scientific point of view, however, it is still extremely unclear exactly what gut health is, how it can be defined and how it can be measured. The GI barrier adjacent to the GI microbiota appears to be the key to understanding the complex mechanisms that maintain gut health. Any impairment of the GI barrier can increase the risk of developing infectious, inflammatory and functional GI diseases, as well as extraintestinal diseases such as immune-mediated and metabolic disorders. Less clear, however, is whether GI discomfort in general can also be related to GI barrier functions. In any case, methods of assessing, improving and maintaining gut health-related GI functions are of major interest in preventive medicine.

Figure 1

The intestine's impact on health. The gastrointestinal tract contributes to health by ensuring digestion and absorption of nutrients, minerals and fluids; by induction of mucosal and systemic tolerance; by defence of the host against infectious and other pathogens; and by signalling from the periphery to the brain. For details and references, see text 'Underlying mechanisms'.

Figure 2

Mechanisms of action of the intestinal microbiome on the gastrointestinal barrier. Commensal bacteria support the digestion of fibres and other nutrients, thereby contributing to energy and substrate supply. They regulate epithelial functions such as mucus production in goblet cells, defensin release from Paneth cells and tight junction protein synthesis in normal epithelial cells. They prevent colonisation of pathogens in the gut and regulate the mucosal immune system, for example, by inducing and maintaining gut-associated lymphoid tissue and by stimulating mucosal immunoglobulin A production. For details and references, see text 'Underlying mechanisms'.