Laxative effect of prebiotics in chronic constipation: Mechanisms of action

Constipation is a condition that affects a consistent part of the general population, with increasing numbers of incidence worldwide. Its causes can be attributed to several factors. One of these factors (and one of the most relevant causes) is dietary choices. For instance, poor nutrition habits have been shown to adversely affect the function of the digestive tract, eliciting abnormal physiological responses that might lead to constipation. Prebiotics are specialized types of fermentable fibres which have been hypothesised to play a beneficial role in the treatment of chronic idiopathic constipation. Fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS) and inulin are the most common types of prebiotics. There are several studies to demonstrate that prebiotics have many interactions with the bowel and its movements, thus they are potentially beneficial in the treatment of chronic idiopathic constipation. Some prebiotics can retain water and therefore increase stool mass and viscosity, making the passage of faeces through the gastrointestinal tract easier. In addition, prebiotics can feed the probiotic bacteria (the body’s “good” bacteria that synergistically live in the digestive tract), and the fermentation of prebiotics by the probiotic bacteria leads to the production of short-chain fatty acids (SCFAs). SCFA synthesis through prebiotic fermentation has been shown to improve gastrointestinal function and bowel movement. Moreover, prebiotic fermentation in the colon might trigger both immunomodulatory responses and the production of neurotransmitters that elicit stronger contractility in the colon. Prebiotic fermentation from the gut microbiota might trigger the release of neurotransmitters that interact with the central nervous system (CNS) and enteric nervous system (ENS). These bacterial neuromodulators directly affect the digestive nerve terminals, eliciting responses from the digestive tract that result in a faster and easier defaecation. Besides the existing studies that describe the roles of prebiotics in gut health and motility, their beneficial role has not yet been fully understood and proven, thus further research is needed on the topic.