Irritable bowel syndrome (IBS) is a chronic disorder affecting 1 in 7 people around the world. The gastrointestinal condition is characterised by recurring symptoms including lower abdominal pain, constipation, diarrhea, bloating, and gas, where no abnormal pathology has been observed.

Although the exact cause of IBS is currently unknown (it’s thought to be a multifactorial condition), a number of pathophysiologic mechanisms of IBS have been identified, one being food sensitivity which has been shown to contribute to the aggravation of IBS symptoms (1).

While the link between FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) sensitivity and IBS has been well established in scientific literature (4), research into salicylate sensitivity and IBS is still in its infancy.

One study (2) looking into the link between salicylate sensitivity and IBS used a sample of 10 IBS patients and randomly allocated them to either a high or low salicylate diet for 14 days. Patients were asked to rate their symptoms (e.g. migraine, asthma, IBS, etc.) on a scale of 1 to 100. After the initial 14 days, the participants resumed their usual daily diet for 7 days before crossing over to the alternate diet (either low or high salicylate) for a further 14 days. Results showed that while most people didn’t experience a difference in their IBS symptoms with a change in diet, one participant with aspirin sensitivity (a drug composed of salicylic acid), experienced worsening of IBS symptoms after 9 days on a high-salicylate diet, contrary to her usual low salicylate diet where she experienced few symptoms. Another participant also experienced worsening of symptoms during the high-salicylate with symptoms improving on the low-salicylate diet. While a big limitation of this study is sample size, the findings hint that salicylate sensitivity may exist in a small portion of patients with IBS. A larger study would be needed to confirm the findings.

Another study (7) which surveyed 643 subjects with IBS showed that 12% reported their symptoms to be associated with the combined use of analgesics, including the salicylic acid, aspirin. However, it should be noted that, while IBS is significantly associated with analgesic use, whether salicylic acid is a contributor is uncertain due to individuals reporting an intolerance to a high number of foods that could be associated with their symptoms.

The mechanisms which explain salicylate sensitivity are understudied. One hypothesis is that symptoms arise due to inhibition of the cyclooxygenase-2 enzyme being higher in salicylate sensitive individuals, which can lead to an overproduction of leukotrienes, metabolites involved in inflammation and pseudo-allergic mechanisms (5)(8). There is also some evidence to suggest that symptoms may be a result of a non-immune direct effect on mast cells to produce cysteinyl leukotrienes (5). These lipid mediators are known to promote smooth muscle contraction and play pivotal roles in acute and chronic inflammation (6), resulting in nausea, bloating, diarrhea or visceral hypersensitivity.

If further research does conclude a link between salicylate sensitivity and IBS, it’s encouraging to know that a low-salicylate diet is well received by participants in terms of palatability (2), and that dietary interventions are an accepted form of treatment by a large percentage of patients (3).

Currently, the only way to ascertain whether salicylates are associated with IBS in a patient is via the expertise of a dietitian, whose knowledge is based upon anecdotal evidence, either from their own clinical observations, or that of others. If a chemical sensitivity is suspected, an elimination diet will usually be advised, followed by a challenge period to ascertain which food chemicals the patient is averse to.

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References

(1) Saha L. Irritable bowel syndrome: pathogenesis, diagnosis, treatment, and evidence-based medicine. World J Gastroenterol. 2014 Jun 14;20(22):6759-73. doi: 10.3748/wjg.v20.i22.6759. PMID: 24944467; PMCID: PMC4051916.

(2) Tuck, C.J., Malakar, S., Barrett, J.S., Muir, J.G. and Gibson, P.R. (2021), Naturally-occurring dietary salicylates in the genesis of functional gastrointestinal symptoms in patients with irritable bowel syndrome: Pilot study. JGH Open, 5: 871-878. https://doi.org/10.1002/jgh3.12578

(3) Harris LR, Roberts L. Treatments for irritable bowel syndrome: patients’ attitudes and acceptability. BMC Complement Altern Med. 2008 Dec 19;8:65. doi: 10.1186/1472-6882-8-65. PMID: 19099570; PMCID: PMC2633319.

(4) Nanayakkara WS, Skidmore PM, O’Brien L, Wilkinson TJ, Gearry RB. Efficacy of the low FODMAP diet for treating irritable bowel syndrome: the evidence to date. Clin Exp Gastroenterol. 2016 Jun 17;9:131-42. doi: 10.2147/CEG.S86798. PMID: 27382323; PMCID: PMC4918736.

(5) Cuomo R, Andreozzi P, Zito FP, Passananti V, De Carlo G, Sarnelli G. Irritable bowel syndrome and food interaction. World J Gastroenterol. 2014 Jul 21;20(27):8837-45. doi: 10.3748/wjg.v20.i27.8837. PMID: 25083057; PMCID: PMC4112903.

(6) Jo-Watanabe A, Okuno T, Yokomizo T. The Role of Leukotrienes as Potential Therapeutic Targets in Allergic Disorders. Int J Mol Sci. 2019 Jul 22;20(14):3580. doi: 10.3390/ijms20143580. PMID: 31336653; PMCID: PMC6679143.

(7) Locke GR 3rd, Zinsmeister AR, Talley NJ, Fett SL, Melton LJ. Risk factors for irritable bowel syndrome: role of analgesics and food sensitivities. Am J Gastroenterol. 2000 Jan;95(1):157-65. doi: 10.1111/j.1572-0241.2000.01678.x. PMID: 10638576.

(8) Hare LG, Woodside JV, Young IS. Dietary salicylates. J Clin Pathol. 2003 Sep;56(9):649-50. doi: 10.1136/jcp.56.9.649. PMID: 12944545; PMCID: PMC1770049