Irritable bowel syndrome (IBS) is one of the most prevalent functional gastrointestinal disorders (FGID), affecting approximately 14% of the global population (Werlang, Palmer, & Lacy, 2019). UK NICE guidelines diagnose Individuals with IBS after having the presence of abdominal discomfort or pain either associated with defaecation and/or accompanied by a change in bowel habit. Individuals with IBS present with varying symptom profiles, most commonly 'diarrhoea predominant', 'constipation-predominant' or alternating symptom profiles. The condition is twice as common in women and most often diagnosis occurs between the ages of 20 and 30 years (National Institue for Health and Care Excellence, 2008).
Often individuals who have IBS symptoms live with the condition for many years prior to a formal diagnosis. Often for a GP to diagnose the condition the symptoms would need to be present for at least 3-6 months so please always seek medical advice if you experience ongoing symptoms.
It is a common occurrence that the majority of IBS patients associate the onset or worsening of symptoms after eating a meal. Actual food allergies are uncommon though but up to 90% of IBS patients exclude certain foods with the aim to improve their GI symptoms (Ford et al., 2018). Many patients report that symptoms develop from or are exacerbated by certain foods. Probiotics, fibre intake and low FODMAP diets have been shown to be beneficial to IBS patients.
If we take the example of a Low FODMAP diet and IBS. A low FODMAP diet represents a diet low in short-chain carbohydrates (fermentable oligo-, di-, monosaccharides and polyols). These diets should only be followed by a registered nutritionist or dietitian as they require an elimination protocol to be followed to ensure the nutrient quality of your diet isn’t compromised. Often IBS patients only need to eliminate one or two sources of FODMAP foods, but this is only determined after a period of elimination and reintroduction has been investigated with your supervised nutrition professional.
What is interesting though is why these FODMAP foods sometimes contribute to IBS symptoms? In some individuals with IBS, it is thought that they poorly absorb or digest certain sugars that pass through the small intestine and enter the colon. These sugars are then fermented by bacteria, releasing excess gas causing bloating, wind and abdominal pain. Fructose, lactose, and polyols tend to retain water in the bowel and may result in loose motions and diarrhoea.
Low FODMAP diets are one example of a dietary plan that may help some patients with IBS. However, talking therapies, probiotics and anti-depressants have found to be just as beneficial.
Could the emerging trend of personalised nutrition help IBS patients further?
Personalised nutrition is a rising new healthcare trend emerging over the past few years. A review published in the BMJ explains broadly that this is an approach that uses information on individual characteristics to develop targeted nutritional advice, products, or services’ (Ordovas et al., 2018). This broad definition ranges in scale from the individually tailored nutritional advice received from your nutritionist to the more scientific applications of precision nutrition, nutrigenetics and nutrigenomics.
It has been well researched that our diet and the foods we eat contribute to diseases such as obesity, heart disease and cancers. What is perhaps not such common knowledge is that we all have individual variations in our genes, also known as single nucleotide polymorphisms or SNPs which can also increase an individual’s predisposition to a disease. These SNPs can be influenced by our diet, lifestyle and environmental factors. Most diseases are not single-gene disorders, and this is likely to be the case in IBS. The genetic contributions would likely occur from multiple genes from multiple pathways and interactions.
Are there any SNPs that could play a role in IBS?
As IBS is a multipathogenic disease research has identified numerous possible genetic candidate genes. SNPs that affect the brain-gut interactions may influence IBS mechanisms. In addition, polymorphisms involving the serotonergic, adrenergic and opioidergic systems, and genes encoding proteins with immunomodulatory and/ or neuromodulatory features have been identified (Cervio et al., 2007). A systematic review and meta-analysis of studies identified 66 candidate SNPs of relevance to IBS. The 10 most common genes across the analysis focused on the following physiological systems; the neurotransmitter system and the inflammation system (Zhu, Wang, Jia, & Duan, 2019). The cytokine of the tumour necrosis factor SNPs rs4263839 and rs6478108 of gene TNFSF15 was associated with an increased risk of IBS. Also, IL6 rs1800795 increased the risk for Caucasian IBS patients diagnosed by Rome III criteria; and IL23R rs11465804 increased the risk for IBS-C patients.
Carbohydrate metabolism and IBS?
SNPs involved in carbohydrate digestion and IBS are emerging as certain foods, in particular, fermentable sugars (high FODMAPS), often exacerbate symptoms. Sucrase-isomaltase deficiency (CSID) is a condition resulting in the inability to digest sucrose and maltose with symptoms of abdominal pain, bloating and diarrhoea similar to IBS diarrhoea symptoms (IBS-D). A case-control cohort screened variations of the SI gene, with the common SI variant (15Phe) identified to be responsible for reduced enzyme activity leading to disaccharide maldigestion, osmotic diarrhoea, gut dysbiosis, excess gas accumulation and SCFA generation (Henström et al., 2018). The 15Val to 15Phe variant was found to be strongly associated to increase the risk of IBS. Findings are suggesting two things, that this 15Phe variant may need to be taken into account for certain IBS low FODMAPs treatment pathways and that IBS diagnostic criteria need to be updated to test for the presence of particular SNPs rather than using solely ROME criteria. Further research is required as this study had a small and limited sample size and did not perform disaccharidase measurements, but with further evidence, it could help develop IBS treatment strategies (Zheng et al., 2020)
This emerging research is certainly a field to watch and explore over the next few years. For individuals that have to live with the condition, the future of personalised nutrition could really help them manage their symptoms.
If you have IBS or want to speak to us about how we can personalise your diet to help you manage your symptoms, please contact Charlotte who we be able to arrange a call to discuss how we can help further. We also are experts at translating all the research into practical, easy to understand formats so don’t worry you don’t need to be an expert in genetics to understand our advice! For information about other gastrointestinal symptoms treat please visit our Gut health page.
References
Cervio, E., Rondanelli, M., Balestra, B., Dellabianca, A., Agazzi, A., Giacosa, A., & Tonini, M. (2007). [Recent insights into the pathogenesis of abdominal symptoms in functional bowel disorders]. Recenti Progressi in Medicina, 98(2), 69–73.
Ford, A. C., Moayyedi, P., Chey, W. D., Harris, L. A., Lacy, B. E., Saito, Y. A., & Quigley, E. M. M. (2018). American College of Gastroenterology Monograph on Management of Irritable Bowel Syndrome: American Journal of Gastroenterology, 113, 1–18. https://doi.org/10.1038/s41395-018-0084-x
Henström, M., Diekmann, L., Bonfiglio, F., Hadizadeh, F., Kuech, E.-M., von Köckritz-Blickwede, M., D’Amato, M. (2018). Functional variants in the sucrase–isomaltase gene associate with increased risk of irritable bowel syndrome. Gut, 67(2), 263–270. https://doi.org/10.1136/gutjnl-2016-312456
National Institue for Health and Care Excellence. (2008). Irritable bowel syndrome in adults: Diagnosis and management | Guideline CG61. Retrieved from https://www.nice.org.uk/guidance/cg61
Ordovas, J. M., Ferguson, L. R., Tai, E. S., & Mathers, J. C. (2018). Personalised nutrition and health. BMJ, 361. https://doi.org/10.1136/bmj.k2173
Werlang, M. E., Palmer, W. C., & Lacy, B. E. (2019). Irritable Bowel Syndrome and Dietary Interventions. Gastroenterology & Hepatology, 15(1), 16–26.
Zheng, T., Eswaran, S., Photenhauer, A. L., Merchant, J. L., Chey, W. D., & D’Amato, M. (2020). Reduced efficacy of low FODMAPs diet in patients with IBS-D carrying sucrase-isomaltase (SI) hypomorphic variants. Gut, 69(2), 397–398. https://doi.org/10.1136/gutjnl-2018-318036
Zhu, S., Wang, B., Jia, Q., & Duan, L. (2019). Candidate single nucleotide polymorphisms of irritable bowel syndrome: A systemic review and meta-analysis. BMC Gastroenterology, 19(1), 165. https://doi.org/10.1186/s12876-019-1084-z