Background/Aims: Whether, chronic chili ingestion can desensitize transient receptor potential vanilloid type 1 receptors in gastrointestinal (GI) tract leading to decrease GI symptoms and sensation in diarrhea-predominant irritable bowel syndrome (IBS-D) patients has not been well explored. The aim of this study was to determine the effects of 6-week chili treatment on postprandial GI symptoms and rectal sensation in response to balloon distention in IBS-D patients.

Methods: Sixteen IBS-D patients received placebo or chili capsules before meals 3 times/day for 6 weeks in a randomized, double-blinded, crossover fashion with 4-week washout period. Postprandial GI symptoms were evaluated. All patients underwent a rectal barostat study to evaluate rectal sensory threshold at the end of each treatment.

Results: The maximum postprandial abdominal burning scores were similar between both treatments at baseline (1.4 [0.0-2.0] vs. 1.1 [0.0-2.8], P > 0.05) but were significantly decreased after chili (0.0 [0.0-0.5] vs. 0.3 [0.0-1.6], P < 0.05) at the end of treatment. The chili treatment significantly increased sensory threshold for the first rectal sensation (median [interquartile range]:16 [12-16] mmHg vs. 8 [8-16] mmHg, P < 0.05) however, there was no significant effect on rectal compliance (7.3 ± 1.0 vs. 7.1 ± 1.8 mL/mmHg). Other postprandial GI symptoms did not vary significantly between both treatments at baseline and the end of treatment.

Conclusions: In IBS-D patients, 6-week chili ingestion significantly decreased postprandial abdominal burning and increased the rectal sensory threshold. These findings suggest a desensitization effect of chili ingestion on transient receptor potential vanilloid type 1 receptors in the proximal gut and rectum.