Published 16 February 2020
By Harriet Smith, Registered Dietitian, on behalf of HRS Communications
Introduction
Cystic fibrosis (CF) is an inherited chronic lung disease, which affects around 10,500 people in the UK (1). It’s caused by a mutation in a single gene, resulting in abnormal function and production of the cystic fibrosis transmembrane conductance regulator protein (CFTR).
The CFTR protein helps to maintain the balance of salt and water on surfaces of the body. Thus, a lack of CFTR results in thick mucus secretions, causing many of the symptoms associated with CF. CF is an autosomal recessive disease, meaning that both parents must carry a single copy of the mutated CFTR gene, allowing the disease trait to develop in the child.
Modern medicine means that all newborns are routinely screened for CF at birth with a heel prick blood test. This has led to earlier detection and treatment of CF, which has improved patient outcomes and life expectancies (2).
Symptoms
As mentioned above, people with CF produce thicker secretions (mucus) than normal. This can trap pathogens such as bacteria and viruses, leading to infections and inflammation.
The respiratory system is often affected, and symptoms may include (3):
The build-up of thick sections can also affect other systems in the body including the digestive system. For example, the mucus can block the transfer of digestive juices from the pancreas, leading to inadequate digestion and absorption of fats and fat-soluble vitamins (A, D, E, and K).
Some people with CF may also experience sinus infections, cystic-fibrosis-related diabetes, impaired growth, osteoporosis, and liver problems. It’s a very complex disease that manifests in different ways for different people.
Pancreatic enzyme replacement therapy
As mentioned above, the thick secretions in the pancreas ducts can impair the digestion and absorption of fats and fat-soluble vitamins. This is sometimes referred to as ‘exocrine pancreatic’ insufficiency, which is thought to affect 80-90% of CF patients (4).
Inadequate absorption of fats, if left untreated, can lead to steatorrhea, weight loss, and undernutrition. Therefore, CF patients with pancreatic insufficiency are advised to take pancreatic enzyme replacement therapy (PERT), to optimise fat absorption.
The amount of PERT prescribed depends on:
No studies to date have determined an optimal dose for PERT. Healthcare professionals (HCPs) are encouraged to prescribe the lowest dose possible and increase gradually until optimal nutritional status, growth, and control of symptoms has been achieved. The maximum recommended dosage of PERT is 10,000 units’ lipase/kg/day but even then, only 90% dietary fat absorption can be achieved (5). PERT is best given in divided doses with all meals, snacks, and drinks containing fat.
High energy requirements
CF patients have high energy (calorie) requirements due to the aetiology of the disease. It’s been suggested that energy requirements are 110-200% higher than the estimated average requirements for the general public (6).
The increased energy requirements in CF patients could be due to a variety of factors, including:
Dietary counselling may be sufficient to manage moderately malnourished CF patients. Food-first approaches may include:
However, if oral intake remains poor, high-energy dense oral nutritional supplements (ONS) may be required. The CFT Guidelines (2016) state that HCPs should consider ONS in addition to optimal daily food intake after addressing behavioral factors and ensuring optimal dosage and timing of PERT (7).
For patients struggling to meet their nutritional requirements through an oral diet and ONS, enteral or parenteral nutrition may be indicated. Enteral feeding has been shown to improve weight gain, nutritional status, and respiratory function in CF patients. It’s usually delivered overnight and typically provides 30-50% of total energy requirements (7).
Other nutrients
The need for an energy-dense diet means that fibre intakes may be low in the CF population. However, dietary fibre recommendations in CF are limited due to the complexity of the CF gut.
There are currently no guidelines for the optimal daily protein intake required by people with CF (7). Protein requirements are thought to be as high as 200% of the recommended nutrient intake for the general population (8). However, further research is needed to establish recommendations for optimal intakes.
Finally, certain vitamins and minerals are commonly supplemented in CF patients. These include high doses of the fat-soluble vitamins A, D, E, and K as well as iron, calcium, and occasionally sodium.
Conclusion
CF is a complex disease that can cause a wide range of challenging symptoms. Dietetic support plays an important role in helping CF patients to optimise their nutritional status and control their symptoms. It’s important to maintain a healthy weight as this can help to prevent chest infections or weight loss caused by illness. Dietetic advice should be individualised to the CF patient, and it may include food-first approaches, PERT, ONS, and/or supplementary feeding.
It’s important to note that managing CF can place a heavy burden on the patients themselves. It’s a progressive disease that can be stressful to manage due to time-consuming treatment regimens and high nutritional requirements.
Working as part of a multi-disciplinary team is crucial for the successful management of CF patients. Psychological interventions may be useful for supporting CF patients when managing their treatment regimens and making dietary changes, however, more research is needed (4).
