For one individual, the culprit might be peanut butter. For another, it might be fried chicken. Foods that trigger symptoms are well identified by those who suffer from irritable bowel syndrome (IBS)—a functional disorder based on gastrointestinal (GI) symptoms that might include abdominal pain, bloating, gas, constipation, or diarrhea.
Scientifically, it has proven more difficult to identify dietary patterns that reliably affect the symptoms of those with IBS. Growing evidence shows, however, that one particular dietary pattern can reduce overall IBS symptoms in the majority of sufferers: the low fermentable oligosaccharides, disaccharides, monosaccharides and polyols (low-FODMAP) diet.
Dr. James Versalovic of Baylor College of Medicine (USA), a leading centre for research on children with functional bowel disorders, says his research group wants to find out how the low-FODMAP diet can be used to reduce recurrent abdominal pain in both children and adults.
“A [low-FODMAP diet is] where you are deliberately changing whole classes of foods,” Versalovic tells GMFH editors in a phone interview. “It’s not simply just ‘eat more fruits and vegetables’ but there are a number of fruits and vegetables that actually elevate your FODMAP content and others that keep it low.” The diet was developed by researchers at Australia’s Monash University and is now being studied by groups around the world for its potential benefits. The premise of the diet is to limit short-chain carbohydrates, which the body does not readily absorb, as well as high-fibre foods that are fermented by bacteria in the large intestine. The group of acceptable fruits includes bananas, berries, and citrus fruits, for example, but excludes apples, pears, and stone fruits. The guidelines disallow honey, sweeteners, wheat, and legumes, while they allow juices, sugar, oats, and rice.
Versalovic and colleagues published a study in 2015 that showed children with IBS on a low-FODMAP diet had less abdominal pain than those who consumed a typical diet. This result was in accordance with previous work showing that up to 86% of patients with IBS show a reduction in overall gastrointestinal symptoms when they consume the diet.
The next pressing question is how the low-FODMAP diet works; if scientists could answer this question, they might discover not only how to refine the diet for best results, but also how to help the small percentage of IBS sufferers who do not improve on the diet. Some researchers suspect the diet’s efficacy might have to do with its impact on the gut microbiota. Backing this idea, a 2015 study by the Monash University team found that the FODMAP content of subjects’ diets changed gut microbiota composition in individuals both with and without IBS. The relationship of these microbial changes to symptom resolution is still unclear, but it’s possible the diet alters gut microbiota in a way that reduces gas production and pain.
A patient’s gut microbiota before dietary change may also have some relevance. Versalovic’s latest efforts focus on using patients’ pre-treatment gut microbiota to predict which patients will respond positively to the diet. “Particular microbial features [may] be associated with response versus no response to the [low-]FODMAP diet,” says Versalovic. “We’ve been working on trying to identify microbial features so that we could take a specimen such as stool [and] identify particular bacterial taxa or metabolites that would predict who would respond or not.”
In the published 2015 study his group found that, before going on the low-FODMAP diet, the patients who responded had more types of bacteria capable of breaking down sugar molecules.
Current studies on the low-FODMAP diet should be interpreted with caution, as researchers have not included genuine placebo groups and have not yet established whether the diet is significantly more effective than other possible diets. Moreover, Versalovic cautions that the results of his paediatric studies may not fully apply to adults with IBS. He says, “The vast majority of our kids have IBS with constipation; many adults have IBS with diarrhea. So that’s a very different scenario.” And while the reduction of symptoms is an end in itself, many health professionals recommend the low-FODMAP diet only for short periods of time because its long-term health effects are still unknown. When it comes to children, the diet’s long-term effects may be particularly important to find out.
Chumpitazi BP, Cope JL, Hollister EB, et al. Randomised clinical trial: gut microbiome biomarkers are associated with clinical response to a low FODMAP diet in children with the irritable bowel syndrome. Alimentary Pharmacology & Therapeutics. 2015; 42(4):418-427. doi: 10.1111/apt.13286
Halmos EP, Christophersen CT, Bird AR, Shepherd SJ, Gibson PR, Muir JG. Diets that differ in their FODMAP content alter the colonic luminal microenvironment. Gut. 2015;64:93-100. doi:10.1136/gutjnl-2014-307264