The present disclosure is directed to methods for supporting resistance to bacterial growth in the gastrointestinal tract of a subject, particularly in that of a human infant. In certain embodiments, the method comprises administering to a subject a nutritional composition that has a low buffer strength, wherein administration of said nutritional composition decreases the bacterial counts of bacteria selected from the group consisting of Enteropathogenic E. coli (EPEC), Enteroaggregative E. coli (EAEC), Cronobacter sakazakii, Salmonella enterica, and combinations thereof in the subject's gastrointestinal tract. This disclosure further relates to the manufacture and use of low-buffer nutritional compositions in methods for modulating gastric acidity and/or in methods for enhancing the rate of gastric emptying in a subject, each method comprising a step of administering at least one of said low-buffer nutritional compositions to the subject.