Beyond Infection: Risk Factors for IBS

Development of irritable bowel syndrome (IBS) is now understood to a matter of epigenetics and environmental factors, and biomarkers can aid in creation of individualized dietary treatment strategies.¹

As genetic analyses decrease in cost, personalized interventions become increasingly possible. Knowing the key genetic variations for chronic conditions enables more targeted treatments, as well as prevention, if tests are done early. A recent study in Caucasian individuals connected genetic variations (in ZMIZ1 and TL1A) associated with impaired disaccharide digestion to IBS symptomatology.² This result suggests that a nutrigenomic approach for individuals with these variations, resulting in a personalized dietary plan, may greatly reduce symptoms. The identified genetic SNPs result in reduced enzyme activity for sucrase-isomaltase (SI) in the small intestine, leading to poor digestion of some carbohydrates (disaccharides like sugars and starches). This could result in the stomach pain, diarrhea, and bloating common to some IBS patients. The researchers identified this SNP first by analyzing seven patients with IBS with diarrhea (IBS-D), as well as one asymptomatic relative, from four families.²

Findings were confirmed with a cohort of 1031 IBS cases and over 850 controls. The study found that patients with rare congenital sucrase-isomaltase (SI) deficiency variations in the SI gene had a two-fold increase in IBS risk, as well as a significantly increased risk from a more common variation, 15Phe at SNP rs9290264. Thus, this one study found two genetic risk factors for IBS-D, both connected to disaccharide metabolism.²

For these patients, a low-FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) diet may help, but may also be unnecessarily restrictive if only disaccharides are the main problem. Since not all patients with IBS-D respond to the FODMAP diet,³ other underlying mechanisms are most certainly at work.

Among the interventions for managing IBS (pre-, pro-, and synbiotics; non-absorbable antibiotics; diets (FODMAP, gluten-free),⁴ low FODMAP diets are prominent. Difficulty in digesting carbohydrates, which are usually foods high in FODMAP, is common in IBS. An individualized approach is also necessary to address co-morbidities, food sensitivities, or other factors which prevent a “one size fits all” approach to nutritional interventions.