Table 1 Mechanisms underpinning the scientific rationale for the selection of the synbiotic formulation targeting the production of indoxyl sulphate and p-cresyl sulphate

Prebiotics “ A selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host wellbeing and health” [17]

Selectively support the colonization of probiotics

Increase the carbohydrate:nitrogen ratio in the colon favouring beneficial saccharolytic vs. proteolytic fermentation

Decrease colonic pH (through short chain fatty acid production) thereby impairing protein degradation with inactivation of pH sensitive proteases

Increase the colonic transit time, thereby decreasing time for bacterial production and intestinal absorption of indoxyl sulphate and p-cresyl sulphate

Enhance bacterial growth with increased uptake of the amino acids for bacterial biosynthesis and therefore less substrate for protein fermentation

Probiotics “Live microorganisms which when administered in adequate amounts confer a health benefit on the host” [18]

Acid and bile resistance to ensure survival through the upper gastrointestinal tract

Competitive exclusion of indoxyl sulphate and p-cresyl sulphate producing bacteria (through competition for essential nutrients and luminal and epithelial binding sites)

Direct bacterial antagonism via inhibitory substance production (such as biosurfactants, hydrogen peroxide, and bacteriocins)

Immunomodulation via immune cell activation resulting in indirect inhibition of pathogenic bacteria