Dietary fibre is good for you, except when it’s not

Researchers uncover the role of dietary fibre and gut microbes in people with inflammatory bowel disease, a finding that could lead to personalized dietary guidelines.


Researchers Eytan Wine (left) and Heather Armstrong found that certain types of dietary fibre can worsen symptoms of inflammatory bowel disease — a discovery that could lead to a simple test and personalized eating guidelines to help people avoid painful flare-ups and longer-term problems. (Photo: Tarwinder Rai)

People who suffer from inflammatory bowel disease may soon have access to personalized dietary guidelines to keep them feeling well, thanks to new research on how dietary fibre affects the disease.

The research team discovered that certain types of dietary fibre cause an inflammatory response in some patients, causing symptoms to worsen.

They are now working to develop a stool test to examine the microbes found in each patient’s gut in order to predict who will have the negative response, so they can tailor dietary recommendations and treatment for individual patients. This next phase of the research will be funded by a $1-million grant from the Weston Family Foundation.

Rates on the rise

About 0.7 per cent of Canada’s population, or one in 150 people, has IBD, including Crohn's disease and ulcerative colitis, and that is predicted to grow to one per cent by 2030. The fastest growing group is children.

IBD symptoms may include abdominal pain, diarrhea, bloody stools, weight loss, late puberty, and a long-term risk of colorectal cancer. The exact cause is unknown, but some risk factors include genetics, diet, environmental factors and changes in the gut microbes. 

“We know there are health benefits to consuming dietary fibres and they promote good gut health in healthy individuals, but IBD patients quite frequently complain about a sensitivity when they consume dietary fibres,” says Heather Armstrong, who started the research as a post-doctoral researcher at the U of A and is now an assistant professor of medicine at the University of Manitoba and Canada Research Chair in Integrative Bioscience. Armstrong has IBD herself. “We really wanted to understand the mechanisms behind this.”

“By creating this stool test, we are hoping to be able to tell you how to adjust your diet to prevent flares or further worsening,” says pediatric gastroenterologist and clinician scientist Eytan Wine, a professor in the Faculty of Medicine & Dentistry. “It’s a dynamic situation so it’s possible that a certain food you should avoid now, in a few months you’ll be OK to eat that again.”

“Not all fibres are born equal”

Unlike most of the food we eat, fibre is not digested in the small intestine. Tiny bacteria and fungi or “microbiota” in the large intestine or colon produce enzymes to ferment fibre. Chemically, fibre can be a short string of sugars like pectin, which is found in citrus fruit, or a very long and branched structure that is harder to ferment. 

The researchers identified that β-fructan fibres found in foods such as artichoke, chicory roots, garlic, asparagus and bananas are especially hard to ferment if certain microbes are missing or malfunctioning, as is often the case for IBD patients.

“We are learning that not all fibres are born equal,” says Wine. “We have shown that some fibre has the potential to cause damage, so we have to be much more selective about when we’re exposing our patients to it.”

Fibre has a beneficial anti-inflammatory effect in most healthy people and aids with digestion, but the researchers found that select unfermented fibres actually increase inflammation and worsen symptoms in some IBD patients.

“We want to start uncovering why it is that 20 to 40 per cent of patients experience sensitivity,” says Armstrong, “while in the other portion of patients these dietary fibres can actually benefit health and protect against the disease and have very positive effects.”

The research was carried out with collaborator Leo Dieleman, professor of medicine, and others at the U of A, and was based on biopsies from more than 100 pediatric patients at the University of Alberta Hospital. Wine is a member of the Women and Children’s Health Research Institute.

Wine and Armstrong both warn that the new dietary guidelines won’t replace drug treatments, but should complement them so patients can avoid flares and get back into remission more quickly when they do experience inflammation.

“I myself have IBD so I often come up with research questions that I personally want answered,” says Armstrong. “If we can find a way to reduce diet-related inflammation, we may be able to relieve some of the disease burden and even save some people from progressing to more serious disease.”