Patients with the irritable bowel syndrome (IBS) commonly report the precipitation of symptoms on food ingestion. Though the role of dietary constituents in IBS has not been extensively studied, food could contribute to symptom onset or even the causation of IBS through a number of mechanisms. First, the physiological response of the intestine to food ingestion could precipitate symptoms in predisposed individuals; second, there is some evidence that allergy or intolerance to a particular food can produce IBS-like symptoms, third, certain foods may alter the composition of the luminal milieu, either directly or indirectly through effects on bacterial metabolism, and thus induce symptoms and, finally, IBS may develop following exposure to food-borne pathogens. Anticipatory, psychological factors generated by previous negative experiences with food ingestion or other factors may also contribute though their contribution has been scarcely quantified. Not surprisingly, there is considerable interest in the potential roles of diet and food supplements in the therapy of IBS; for the most part, the evidence base for such recommendations remains slim though certain probiotics show considerable promise.