A new study using MRI to investigate the effects of carbohydrates in the diet on symptoms of patients with irritable bowel syndrome has found they are more sensitive to gas in their bowel.
The trial has been carried out by the NIHR Nottingham Digestive Diseases Biomedical Research Centre and experts at the Sir Peter Mansfield Imaging Centre at The University of Nottingham. The research is published online in Gastroenterology.
Many patients complain that certain foods trigger their symptoms. Trigger foods such as pasta, bread and onions all contain carbohydrates that are not easily digested. These carbohydrates, sometimes grouped together under the acronym FODMAP (fermentable oligo-di- & mono-saccharides & polyhydric alcohols), are fermented in the lower bowel, releasing gas. Until now it is has not been possible to investigate how this might cause symptoms but the Nottingham study used cutting edge imaging techniques to observe gas production.
Carb drink challenge
A group of 29 adults with IBS were recruited alongside a second group of 29 healthy individuals as controls. On three separate occasions, at least 7 days apart, each participant was given a drink containing 40g of carbohydrate – glucose in the first challenge, fructose in the second and inulin (an indigestible plant carbohydrate) in the third – in a random order.
Participants were scanned hourly to measure changes in their bowel. They were also asked about any symptoms of pain or bloating. The study found that more patients reported significant symptoms after the inulin drink than after glucose. The severity of their symptoms was related to the peak amount of gas in their bowel. However, healthy adults has just as much gas in their bowel as the patients, without feeling symptoms.
Sensitive to stretch
Leading the study, Professor Robin Spiller of the NIHR Nottingham Digestive Diseases Centre, said: “We think our results were very revealing. More patients with IBS reached our pre-defined symptom threshold (pain, bloating) after drinking the inulin or fructose than the glucose drink. Inulin produces colonic gas and where patients had symptoms, the severity correlated with the amount of gas produced. The physiological changes induced by the drinks were similar in people with or without IBS. This is consistent with certain IBS patients having a bowel that is particularly sensitive to stretch. These patients might benefit from dietary changes or drug therapy. Patients who are not sensitive in this way can be reassured about their diet.”
The MRI study provides some of the first clear evidence of how fermentable carbohydrates can distend the colon. It also provides a mechanistic basis for the clinical observation that reducing such carbohydrates in the diet can reduce feelings of bloating and discomfort.
The researchers say people who report symptoms relating to fermentable carbohydrate may be accurately assigning the cause of their problems. The same patients may also have visceral hypersensitivity so a dual treatment with dietary modification and pharmacotherapy could help.
The research team stresses that this study does not take into account the role of the microbiota of the individual or the potential nocebo (negative expectation) effect of drinking a challenge drink. It may be that certain microbiomes induce more gas production however the study also concludes that prospect of linking microbiome signatures to dietary sensitivity holds real promise for personalised care of patients.
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