Irritable bowel syndrome (IBS) is a poorly understood gastrointestinal disorder that affects a significant percentage of the population and has a strong negative effect on the quality of life. The lack of known pathophysiologic mechanisms has made finding effective treatment strategies difficult. One of the common recommendations by clinicians is a trial of a lactose-free diet. We have wondered if there was sufficient evidence in the currently available literature to support such a recommendation. We have also looked into other possible relationships between malabsorption syndromes and IBS. All the articles used for this review have been found in the PubMed database. We have taken into consideration the possibility that there may be both genetic differences and differences in the gut microbiome between populations living in different geographic regions. Therefore, we have included articles from different geographic regions to increase the generalizability of the findings. While there is a plethora of evidence that IBS patients commonly report milk intolerance, we have not found any conclusive evidence to suggest an objective link between IBS and any known malabsorption syndromes, including lactose malabsorption. Furthermore, trials of lactase supplementation have not led to clinical benefit. We concluded that there was no evidence to support routinely recommending a lactose-free diet for patients diagnosed with IBS, but including hydrogen breath testing in routine workup of IBS is a reasonable clinical decision. Ultimately, we believe that more clinical trials and chemical studies of the feces are needed to determine the pathophysiology and explore possible dietary recommendations for patients with IBS.