Background & Aims Patients with diarrhea-predominant irritable bowel syndrome (IBS-D) anecdotally report symptom improvement after initiating a very low-carbohydrate diet (VLCD). This study prospectively evaluated a VLCD in IBS-D.

Methods Participants with moderate to severe IBS-D were provided a 2-week standard diet, then 4 weeks of a VLCD (20 g carbohydrates/d). A responder was defined as having adequate relief of gastrointestinal symptoms for 2 or more weeks during the VLCD. Changes in abdominal pain, stool habits, and quality of life also were measured.

Results Of the 17 participants enrolled, 13 completed the study and all met the responder definition, with 10 (77%) reporting adequate relief for all 4 VLCD weeks. Stool frequency decreased (2.6 ± 0.8/d to 1.4 ± 0.6/d; P < .001). Stool consistency improved from diarrheal to normal form (Bristol Stool Score, 5.3 ± 0.7 to 3.8 ± 1.2; P < .001). Pain scores and quality-of-life measures significantly improved. Outcomes were independent of weight loss.