Introduction
Fermentable oligo-, di-, monosaccharides and polyols (FODMAP) may provoke gastrointestinal (GI) symptoms through physiological mechanisms in patients with irritable bowel syndrome (IBS)1, and fructans have been suggested to be of particular importance2. Negative expectations can exacerbate symptoms (nocebo effects)3 but the extent to which food components aggravate symptoms through physiological processes versus the contribution of patients' expectations of symptoms remains unclear.
Aims & Methods
We aimed to assess the link between GI symptoms, fructan intake, and colonic fermentation using an ingestible gas-sensing capsule and breath tests in patients with non-constipated (diarrhea-predominant and mixed) IBS on a low FODMAP diet.
Non-constipated IBS patients (Rome IV, n=89, age 18–50 years, 83% females) were included in this randomized, placebo-controlled trial (NCT04830410). Baseline assessment was made while patients retained their habitual diet. Next, the patients adhered to a low FODMAP diet for three weeks with all foods provided. During week 3, patients were challenged with fructans or maltodextrin (sham), with either high (18g; 6g tds, n=24) or low dosages (6g; 2g tds, n=65).
Patients reported severity of GI (IBS-SSS) at baseline and at the end of week 2 and 3, as well as stool form (BSFS) for all bowel movements. Colonic fermentation was assessed at baseline and at the end of week 3: luminal colonic hydrogen and carbon dioxide concentrations (overall and regional [per quartile of colonic transit time]) were measured using a gas-sensing capsule4, with breath concentrations of hydrogen and methane concentrations also examined. The gas-sensing capsule also provided whole gut and segmental transit times.
Results
The low FODMAP diet reduced overall IBS symptom severity at the end of week 2 compared to the habitual diet (IBS-SSS; mean change = -89 ± 94, P<0.0001), as well as individual symptoms P<0.0001 for all). Moreover, the low FODMAP diet reduced the frequency of loose stools at the end of week 2 (% loose stools; mean change 10% ± 19%, P<0.0001).
At the end of week 3, no significant differences in symptoms or transit times were observed between the fructans and sham challenges. This was observed for both 18g and 6g interventions (Table). Breath hydrogen and methane were higher in the 18g fructans group compared with sham (P<0.01 for both). Luminal hydrogen concentration (overall and in quartile 4) was higher in the 18g fructans group compared with sham (P=0.03 and P=0.04) while there were no differences in carbon dioxide concentrations. No differences in colonic fermentation were observed between the 6g fructans and sham groups.
In the 6g population, the intervention period increased overall IBS symptom severity, independent of fructans or sham intervention [ß-coefficient: 37 (95% CI: 5-70), p=0.03].
| Table 1. Fructans vs. sham | 18 g Fructans (n=12) | 18 g Sham (n=12) | 6 g Fructans (n=32) | 6 g Sham (n=33) |
IBS-SSS Total Pain intensity Pain frequency Abdominal distension Bowel habit dissatisfaction Daily life interference | 210 ± 93 35 ± 25 28 ± 33 43 ± 35 49 ± 15 55 ± 19
| 173 ± 104 24 ± 21 32 ± 34 25 ± 20 44 ± 24 50 ± 27
| 200 ± 123 31 ± 28 36 ± 36 35 ± 35 44 ± 21 54 ± 26
| 223 ± 101 40 ± 27 39 ± 32 38 ± 30 49 ± 22 57 ± 24
|
BSF Loose stools, % BSF Normal stools, % BSF Hard stools, %
| 14 ± 14 59 ± 30 10 ± 13 | 22 ± 27 67 ± 27 10 ± 17 | 14 ± 22 69 ± 28 17 ± 22 | 18 ± 23 69 ± 27 10 ± 12 |
Colonic transit time (h) Whole gut transit time (h)
| 18.7 (15.6-39.4) 26.8 (24.2-35.3) | 17.9 (16.0-18.9) 26.1 (24.3-28.3) | 21.8 (14.6-40.1) 28.6 (23.5-50.8) | 23.4 (14.6-36.6) 32.5 (25.0-50.0) |
Overall luminal H2, % Overall luminal CO2, % | 6.93 ± 3.88 * 19.34 ± 4.40 | 3.10 ± 2.33 16.65 ± 3.38 | 6.10 ± 3.43 24.44 ± 9.34 | 5.28 ± 4.37 25.71 ± 7.47 |
Breath H2, AUC (ppm) Breath CH4, AUC (ppm) | 3399 ± 2432 * 1033 ± 698 * | 1503 ± 434 529 ± 511 | 1740 ± 1944 658 ± 813 | 1693 ± 1504 890 ± 1142 |
Conclusion
In non-constipated IBS patients following a low FODMAP diet, supplementation with 18 g (but not 6 g) fructans per day led to increased colonic fermentation, without severe aggravation of GI symptoms. Independent of intervention, IBS symptom severity increased, highlighting the role of the nocebo effect. Central and peripheral processes may both be important in FODMAP-related symptoms with individual variations.
References
1. Ong DK, Mitchell SB, Barrett JS, Shepherd SJ, Irving PM, Biesiekierski JR, et al. Manipulation of dietary short chain carbohydrates alters the pattern of gas production and genesis of symptoms in irritable bowel syndrome. J Gastroenterol Hepatol. 2010;25(8):1366–73.
2. Van den Houte K, Colomier E, Routhiaux K, Mariën Z, Schol J, Van den Bergh J, et al. Efficacy and findings of a blinded randomized reintroduction phase for the low FODMAP diet in Irritable Bowel Syndrome. Gastroenterology. 2024 Jul;167(2):333-342.
3. Elsenbruch S. Unravelling the power of nocebo in symptom response to food challenge in irritable bowel syndrome. The Lancet Gastroenterology & Hepatology, 2025; 10, 780-781
4. Berean KJ, Ha N, Ou JZ, Chrimes AF, Grando D, Yao CK, et al. The safety and sensitivity of a telemetric capsule to monitor gastrointestinal hydrogen production in vivo in healthy subjects: a pilot trial comparison to concurrent breath analysis. Aliment Pharmacol Ther. 2018;48(6):646–54.