Cure4CF Update

Gut Instincts: Why Digestive Matters in Cystic Fibrosis

Opinion piece by Professor Jodie Simpson

I attended a really interesting scientific session at the European Cystic Fibrosis Society (ECFS) Conference in June 2026, and it started me thinking….

When people think about cystic fibrosis (CF), they usually think about the lungs. But for many people living with CF, it’s their digestive system that affects them every single day.

Bloating. Stomach pain. Nausea. Constipation. Urgency. Planning meals around outings. Avoiding eating before leaving the house.

These symptoms can have a major impact on quality of life, yet digestive health in CF often receives far less attention than lung health.

Importantly, this isn’t just an issue raised by clinicians and researchers. Digestive health is a research priority identified by the CF community itself. Through Priority Setting Partnerships and community consultations, people with CF have highlighted questions such as:

  • How can we relieve gastrointestinal symptoms such as stomach pain, bloating and nausea?
  • What effects do CFTR modulators have on parts of the body outside the lungs, including the pancreas, liver and digestive system?
  • How can we improve digestive function and gut comfort?
  • How can we better manage medicine side effects?

These priorities reflect a simple reality: digestive symptoms matter.

When I looked at the research being published, in the last 5 years there are 20 times more publications involving CF and l

The Challenge: One Symptom, Many Possible Causes

One of the reasons gastrointestinal (GI) symptoms can be difficult to treat is that the same symptom may have many different causes.

Take bloating, for example.

Bloating could be related to:

  • Constipation
  • Problems digesting food due to pancreatic enzyme timing or dosing
  • Diet and food fermentation in the gut
  • Slowed movement of food through the digestive tract (known as dysmotility)
  • Small Intestinal Bacterial Overgrowth (SIBO), where too many bacteria grow in the small intestine
  • Stress, anxiety, or heightened awareness of digestive symptoms

As a result, simply asking “Do you feel bloated?” may not tell us what’s really happening. Understanding the cause is often the first step toward finding the right solution.

The Oesophagus: More Than Just Reflux

The oesophagus is the tube that carries food from the mouth to the stomach.

Gastro-oesophageal reflux disease (GERD), often called reflux or heartburn, is common in people with CF. Studies suggest it may affect between 15% and 51% of people.

Reflux occurs when stomach contents flow back into the oesophagus. Left untreated, it can contribute to complications including inflammation and damage to the oesophagus.

While many people are treated for reflux based on symptoms, more specialised tests that objectively measure reflux are not always performed.

Some small studies suggest that CFTR modulators may improve reflux symptoms in some people. However, even among people taking modulators, abnormal acid exposure in the oesophagus has still been observed. Larger studies are needed to understand the true impact.

The Stomach: When Emptying Slows Down

Another common but often overlooked problem is gastroparesis.

Gastroparesis means the stomach empties more slowly than normal. It is estimated to affect around 38% of people with CF.

Symptoms can include:

  • Feeling full quickly
  • Nausea
  • Bloating
  • Vomiting
  • Reduced appetite

Gastroparesis can contribute to poor nutrition, constipation, reflux and challenges managing CF-related diabetes.

Doctors may diagnose gastroparesis using specialised tests such as breath tests, motility capsules or imaging studies that track how food moves through the stomach.

The Intestine: A Different Environment in CF

The intestine in CF is different in several important ways.

Research shows that people with CF often have:

  • More acidic conditions in the intestine
  • Increased permeability (“leaky gut”)
  • Changes in mucus composition
  • Ongoing inflammation

These changes can affect digestion, absorption and the gut microbiome.

The good news is that some studies suggest CFTR modulators may help normalise intestinal pH and reduce markers of inflammation such as calprotectin.

However, improvements in how quickly food moves through the gut have been less clear, and many questions remain unanswered.

What About SIBO?

Small Intestinal Bacterial Overgrowth (SIBO) is increasingly discussed in the CF community as a possible contributor to bloating, pain and digestive discomfort.

Yet despite growing interest, there are currently very few studies investigating how CFTR modulators affect SIBO.

This highlights a broader issue: there are still major gaps in our understanding of digestive health in the modulator era.

The Colon: Constipation Remains Common

Constipation is one of the most frequently reported digestive symptoms in CF.

Why does it happen?

CF causes thicker secretions throughout the body, including the digestive tract. This can lead to drier bowel contents and slower movement through the colon.

Constipation is usually diagnosed based on symptoms after other causes have been excluded. Treatment may include:

  • Hydration
  • Fibre
  • Physical activity
  • Laxatives

Studies suggest around two-thirds of people with CF experience constipation.

While some improvement has been reported following CFTR modulator treatment, more than half of participants in some studies continued to experience constipation. Small studies have also shown modest improvements in how quickly material moves through the colon after prolonged modulator treatment.

DIOS: A Unique CF Complication

Distal Intestinal Obstruction Syndrome (DIOS) is a condition specific to CF in which thick intestinal contents partially or completely block the bowel.

Symptoms can include:

  • Abdominal pain
  • Bloating
  • Nausea
  • Vomiting

Despite hopes that CFTR modulators might reduce DIOS, one study found no significant change after three years of treatment across several different modulator therapies.

Again, larger studies are needed.

Are We Absorbing Food Better?

One of the most interesting questions is whether modulators improve the body’s ability to absorb nutrients.

Some studies have found:

  • Increased body weight and BMI
  • Reduced fat loss in the stool

These findings suggest that digestion and absorption may improve for some people.

However, researchers have not consistently seen improvements in faecal elastase, a marker used to assess pancreatic enzyme production.

In simple terms, people may be absorbing nutrients better, but it is still unclear whether the pancreas itself is recovering significant function.

Are Digestive Symptoms Being Overlooked?

As researchers continue to learn more about CFTR modulators, an important question remains:

Are people with CF being routinely asked about their digestive symptoms—and are we measuring them in a meaningful way?

Many people continue to experience bloating, abdominal pain, constipation, nausea and other gut-related symptoms despite major advances in CF care.

Yet digestive symptoms can be difficult to assess, difficult to diagnose and sometimes difficult to discuss.

Perhaps the most important message is that these symptoms are not “just part of CF”. They matter. They affect daily life, social activities, nutrition, work, school and wellbeing.

The CF community has already told us that digestive health is a priority. Now the challenge is ensuring research, clinical care and routine assessment keep pace.

Read more of Professor Jodie's thoughts