Research over the past two decades has provided evidence that administration of probiotics (live microorganisms which, when administered in adequate amounts, confer a health benefit on the host) could be used to optimise gut microbiota and prevent and treat a range of diseases, as well as enhance immune function. Somewhat less documented and more recent concept is the use of prebiotics (nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one, or a limited number of bacteria in the colon). Prebiotics are naturally available in breast milk and in certain vegetables but can also be synthetic oligosaccharides of which the best known and the most researched examples include fructooligosaccharides (FOS) and galactooligosaccharides (GOS). B-GOS is a low molecular weight GOS mixture, shown to increase the number of probiotic bacteria, especially bifidobacteria, in younger and older adults, irritable-bowel sufferers and overweight adults. B-GOS also significantly decreases the colonisation and pathology of salmonellosis and incidence and duration of traveller's diarrhoea.