This chapter reviews the current practice and evidence for dietary therapy of functional gastrointestinal disorders (FGIDs) and possible negative consequences of treatment. The three modes of treatments targeting FGIDs are dietary, psychological and pharmacological. The dietary strategy that has had the greatest impact in the management of irritable bowel syndrome (IBS) symptoms has been the low fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) diet. The mechanism by which FODMAPs induce symptoms relates to the physiological effects of luminal distension, which emerges through three characteristics of FODMAPs: poor and slow intestinal absorption, osmotic effect and rapid colonic fermentation, producing gas. Before the low FODMAP diet, the diet that had been the most thoroughly researched to manage symptoms of IBS was a high-fibre diet. Another diet with widespread application in Australia is termed the low food chemical diet, which restricts dietary food chemicals naturally occurring and/or food additives.