Irritable bowel syndrome (IBS) is heterogeneous. Patients need proper assessment and explanation of IBS pathophysiology and appropriate therapies. A low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet effectively reduces symptoms in 75% of patients. Best treatment for those nonresponsive will depend on the pathophysiological basis for symptom genesis, with the following possible abnormalities: (i) Visceral hypersensitivity and/or enhanced gut-brain communication: a low FODMAP diet is mainly targeted for this patient group. A dietitian may also recommend antispasmodic agents, including peppermint oil. Another dietary treatment is a low food chemical diet, although this diet is often extremely limited, and therefore, not suited for some populations. Psychological therapies are also clinically beneficial. (ii) Altered motility: in patients with fast transit, a dietitian may recommend a reduction in all FODMAPs or targeted monosaccharides and disaccharides, which are more osmotic in nature. If not effective, patients may benefit from psyllium, which has an exceptional water-holding capacity aimed to promote more formed stools. Patients with slow or uncoordinated transit are often more difficult to treat. Dietary interventions have some success and usually comprise a combination of adequate fiber and fluid, osmotic laxatives, and stimulating agents such as caffeine, senna, and exercise. (iii) Altered microbiome: supplementary probiotics and prebiotics have weak evidence of efficacy with some notable exceptions. A dietitian may trial supplementary Bifidobacterium infantis or oligosaccharides, usually as an adjunct therapy. Guidance from a dietitian will encompass dietary methods to treat IBS but additionally identify where dietary treatment is not indicated to ensure that diet is correctly used and patients are not nutritionally or psychologically compromised.