Gut microbial metabolites and biochemical pathways involved in irritable bowel syndrome: effects of diet and nutrition on the microbiome

The food we consume and its interactions with the host and gut microbiota affects normal gut function and health. Functional gut disorders (FGDs) and more specifically Irritable Bowel Syndrome (IBS) can result from negative effects of these interactions, leading to a reduced quality of life. People who suffer from FGDs believe that certain foods or diets either exacerbate or reduce the severity and prevalence of their symptoms. IBS is an ideal model to use as a perturbation from normal gut function for which to study the impact of foods and diets and how key processes and biochemical mechanisms contribute to the severity and symptoms of FGDs. Understanding these interactions will help to identify foods that can improve gut function and health in not only people that suffer from FGDs, but also healthy asymptomatic people. Towards this goal, analysis of the interactions between host and microbial metabolites gives quantitative insights into the pathways and processes occurring in the gut and interconnected body functions. This review will present a critical discussion of the literature surrounding metabolic pathways and dietary interventions relevant to IBS. Many metabolites, for example bile acids (BAs), short chain fatty acids (SCFAs), vitamins, amino acids, and neurotransmitters, can be altered by dietary intake, and could be valuable for identifying perturbations in metabolic pathways that distinguish a ‘normal healthy’ gut from a ‘dysfunctional unhealthy’ gut as well as between IBS subtypes. There are an increasing number of dietary interventions aimed at reducing the symptoms and prevalence of IBS but the variation in effectiveness of these interventions highlights the need for a better understanding of the underlying mechanisms and the critical metabolites that provide insights of these mechanisms.