Nutrition in Cystic Fibrosis

Cystic fibrosis (CF) is mostly recognized for its pulmonary morbidity, but the earliest manifestations of the disease are related to its gastrointestinal and nutritional derangements. Destruction of acinar pancreatic tissue, pancreatic ductular obstruction, and lack of enzymatic activity lead to malabsorption (particularly of fats), diarrhea, and failure to thrive. A minority of CF patients carrying milder CF transmembrane conductance regulator (CFTR) mutations have preserved pancreatic secretory activity and are free from significant malabsorption early in life. However, these patients are at risk for losing pancreatic function over time. Nutritional status plays an important role in the progression of the pulmonary disease in CF. Further, CF patients with better nutritional status have a survival advantage. Several factors contribute to impaired nutritional status in CF (e.g., pancreatic insufficiency, chronic malabsorption, recurrent sinopulmonary infections, chronic inflammation, increased energy expenditure, suboptimal intake). Progressive lung disease further increases caloric requirements by increasing the work of breathing. Treatment programs that place an emphasis on higher caloric intake and more aggressive nutritional management in CF patients report better outcomes. Basic tenets of nutritional repletion in CF include the use of pancreatic enzyme replacement therapy and following a high calorie, high protein, unrestricted diet. At the Stanford Cystic Fibrosis Center, nutritional status is assessed on an ongoing basis through anthropometric parameters and annual assessment of body composition, bone density, glucose tolerance, and various biochemical and micronutrient levels. Based on the anthropometric data obtained on routine clinical encounters, patients are categorized as to their nutritional risk. This proactive approach for the early identification of nutritional risk has become a major theme within the network of US CF centers. Aggressive nutritional support with adequate pancreatic replacement management should lead to both normal growth and lung function preservation. In addition, nutritional status has to be monitored closely during routine encounters to allow for early intervention once derangements are noted. This will include increasing calories in the early stages of lung disease and being vigilant of gastrointestinal symptomatology and complications.