Medical Nutrition Matters: Spring 2023 Volume 42, No. 4

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Article: Navigating Adaptations to Nutrition Practice in a Changing Cystic Fibrosis World

Cystic fibrosis (CF) is a genetic disease characterized by “mutations to the Cystic Fibrosis Transmembrane Regulator (CFTR) gene” that affects multiple systems in the body including gastrointestinal tract and respiratory system. The CFTR protein impacts the balance of sodium and chloride within the epithelial cells; when defective, this can result in dehydration and increased mucus throughout the body (1,2). Affecting one in 3,000 live births in the United States (3), cystic fibrosis is the most common genetic disease in the Caucasian population; recognizing the increasing prevalence in recent years of diagnoses in other ethnicities. In 2003, the Centers for Disease Control (CDC) and Cystic Fibrosis Foundation (CFF) developed best practice guidelines for diagnosing CF, including the implementation of Newborn Screening (NBS). By 2010, all fifty states had implemented NBS for CF (4). The NBS identifies approximately 60% of patients with CF (5). Confirmed diagnosis is made with an elevated sweat chloride test (4,6) or extended genetic testing. With the development of Highly Effective Modulator (HEM) therapy, these genetics help determine treatment later in life. CFTR modulator therapy works to correct the malformation and/or malfunction of the protein produced. CFTR modulator therapy has been approved by the US Food and Drug Administration (FDA) for specific gene mutations, and as of 2020, 85% of the CF population qualify for therapy (5).

Prior to NBS, undiagnosed CF patients presented with poor nutritional status, often malnourished and dehydrated (7), with the average age of diagnosis being six months (8). In the CF population, 85% of patients are born with exocrine pancreatic insufficiency (EPI), causing fat malabsorption (9,10) which was the primary reason for poor growth. Early nutrition intervention is key to ensure the best possible outcomes for patients with CF. Pancreatic Enzyme Replacement Therapy (PERT) was used as a CF treatment starting in 1938 (10). Poor regulations of PERT resulted in malabsorption and led to high PERT dosing and recommendations for low fat diets to better manage symptoms (10). This continued as primary nutrition intervention through the 1960s, until the case was made to regulate PERT composition (10). In 1979, Graham determined an enteric coating would protect the active enzymes until they reached the duodenum, thus allowing for significant decreases in PERT dosing and improvement in symptoms (11). With a reduction in malabsorption, a higher calorie, higher fat diet was recommended to further optimize nutritional status.  This diet, now referred to as The Legacy Diet, has been proven to be an effective nutrition intervention for CF and is a common recommendation in today’s practice. However, as CF care continues to evolve with the inclusion of gene specific therapy, the question is, will nutrition recommendations change?

CPE Level: 2
CPEU: 1
Performance Indicators: 8.1.1, 8.2.1, 8.2.2

Learning Objectives

• Discuss the cystic fibrosis diagnosis process, qualifying genetics for highly effective modulator therapies, and modulator therapy evolution.
• Summarize current Cystic Fibrosis Foundation nutrition guidelines and identify strengths and limitations of these nutrition specific recommendations.
• Outline potential changes to nutrition recommendations in the era of highly effective modulator therapy and list ideas to help shape healthy eating behaviors for the future.