Background: Visceral hypersensitivity is involved in the pathogenesis of irritable bowel syndrome (IBS). Ingestion of chili has been reported to induce abdominal pain and burning symptoms in IBS, possibly by way of capsaicin receptor (TRPV1) stimulation. Chronic ingestion of chili can improve symptoms of NERD and functional dyspepsia. However, there is no study in IBS-D patients.

Objective: To determine the effects of chronic chili ingestion on abdominal pain, abdominal burning and rectal sensation in IBS-D patients.

Methods: Ten IBS-D patients were included. All patients received capsules of placebo powder or chili powder (chili 2.1 gm/day, capsaicin 2.5 mg/day) orally in 3 divided doses before meals for 6 weeks, in a randomized double-blinded crossover fashion with a 4-week washout period. Gastrointestinal severity symptom and rectal sensation scores were assessed and compared between the placebo and the chili treatment groups at week 0, 1, 2, 4, and 6, using a 100-mm long visual analog scale. Rectal barostat was evaluated in all patients at the end of each treatment period. Gastrointestinal symptoms in response to spicy food were evaluated before and at the end of treatment.

Results: All patients completed the study without serious adverse events. Compared to placebo, chronic chili ingestion had no significant effects on abdominal pain, abdominal burning, abdominal bloating, postprandial fecal urgency, diarrhea and incomplete evacuation symptom scores. Chronic chili ingestion appeared to significantly increase sensory threshold of rectal perception for the first rectal sensation (12 vs. 8 mmHg; p = 0.03) without significant effect on rectal compliance. After chronic chili ingestion, abdominal burning symptom score in response to a standard spicy meal was significantly decreased, compared with that after placebo ingestion (4.3 ± 2.4 vs. 14.1 ± 5.1; p = 0.02).

Conclusions: Chili ingestion for 6 weeks significantly increased the sensory threshold of rectal perception for the first rectal sensation in IBS-D patient, without significant effects on rectal compliance and IBS symptoms. In addition, abdominal burning after standard spicy meal was significantly decreased. The results suggested that 2.1 gm/day of chili ingestion for 6 weeks can desensitize the capsaicin receptors in the proximal gut and the rectum.