The invention relates to nutritional and pharmaceutical compositions comprising non-digestible galactooligosaccharides (GOS) and uses thereof. In particular, it relates to the use of GOS species in preventing or treating disease caused by bacterial toxins. Provided is the use of GOS having a polymerization degree of 5 or higher, preferably 6 or higher, for the manufacture of a nutritional or pharmaceutical composition for the treatment or prevention of an acute or chronic disease associated with or caused by the adhesion and/or uptake of a cholera toxin family member. Also provided is a method for providing a GOS fraction capable of inhibiting cholera toxin (Ctx) binding to GM1 and fractions obtainable thereby.