The majority of patients with CF are pancreatic insufficient which means that the pancreas does not produce enough digestive enzymes. Unless this is treated with pancreatic enzyme supplements, digestion and absorption of food is severely impaired. Inadequate absorption of food from the bowel will lead to unpleasant digestive symptoms, malnutrition, poor growth and specific deficiencies of the fat soluble vitamins A, D, E and K (Littlewood & Wolfe, 2000; Littlewood et al, 2006) and essential fatty acids (Lloyd-Still, 2002).
Patients who are well nourished have a better outcome (Corey et al, 1988; Steinkamp & Wiedemann, 2002). Wasting (poor weight gain), (Sharma et al, 2001) and stunting (poor height gain), (Beker et al, 2001) are independent predictors of mortality in CF. In addition, good growth and nutritional status early in life are associated with better lung function during childhood (Konstan et al, 2003; Peterson et al, 2003; Pedreira et al, 2005). Conversely, malnutrition results in poor growth, impaired respiratory muscle function (Zemel et al, 2000), decreased exercise tolerance and immunological impairment resulting in increased susceptibility to infections (De Meer et al, 1999). Nutritional support has been shown to improve nutritional status (Jelalian et al, 1998) and stabilise or slow the rate of decline in lung function (Walker & Gozal, 1998; Steinkamp & Wiedemann, 2002; Efrati et al, 2006). It is therefore essential that dietetic management is an integral part of CF care. Dietary treatment should ensure that all patients achieve normal weight gain, growth, body composition, pubertal development and vitamin, mineral and essential fatty acid (EFA) status. With increased life expectancy it is also important that dietary management aims to minimise the risks of developing osteoporosis, achieves good control of CF related diabetes (CFRD) and ensures good weight gain during pregnancy.
The energy requirements of patients with CF vary widely and generally increase with age and disease severity. Poorly controlled absorption of dietary fat (Littlewood et al, 2006) and increased energy expenditure (Bell et al, 2000; Dorlochter et al, 2002; Allen et al, 2003) both increase energy requirements. Thus, a newly diagnosed infant with good control of absorption may have normal energy requirements. In contrast, an adult with some fat malabsorption and poor respiratory function may have energy requirements in excess of 150% (Wolfe, 2003) of the normal estimated average requirement appropriate for the patient’s age (Department of Health, 1991).
In order to meet energy needs all patients should be seen regularly by a dietitian experienced in the management of CF, who will monitor growth and tailor dietary advice to the individual. Dietary fat should never be restricted as this nutrient is essential to achieve a good energy (calorie) intake. If weight gain is poor or weight loss is experienced, patients should be encouraged to eat foods that are high in calories, such as fried foods, crisps and chocolate and those rich in protein such as milk, cheese and eggs. Many of these foods are also good sources of calcium, which is important to keep bones healthy.
Unfortunately, many patients do not manage to eat enough to meet their increased energy requirements (White et al, 2004; White et al, 2007). The reasons for this are multifactorial and include chronic poor appetite, infection related anorexia, gastro-oesophageal reflux, abdominal pain, vomiting, depression and feeding behaviour problems (Duff et al, 2003). A detailed dietary assessment and food frequency questionnaire should be performed for all patients in order to identify the factors that may contribute to a reduced energy intake. Ideally, a four to five day dietary and enzyme diary should be recorded every one to two years or more frequently if growth is poor. This provides an estimation of dietary adequacy and enables the dietitian to advise on the most appropriate ways of increasing the energy intake if necessary. The intake of other important nutrients such as calcium and iron and the adequacy of pancreatic enzyme replacement therapy can also be checked.
Evaluation of growth
Weight must be recorded at every clinic visit (minimum every three months). Height must also be recorded at every clinic visit until growth has ceased and thereafter periodically to check for height loss. For children, the measurements must be plotted on the appropriate percentile charts so that growth progress can be closely monitored. In addition, head circumference should be measured and plotted on the percentile chart for children under one year of age (Littlewood & Wolfe, 2000; Cystic Fibrosis Trust, 2002). For adult patients, weight and height measurements should be converted to body mass index (BMI). There is recent evidence that BMI percentile positions in children predict nutritional failure more sensitively than conventional weight and height measurements (Lai, 2006; Wiedemann et al, 2007).
Recently there has been increasing concern regarding the health of bones. All children over the age of 10 years and adult patients with CF should have a dual energy x-ray absorptiometry (DXA) scan for measurement of bone mineral density with repeated scans performed according to clinical need and at least every three years (Cystic Fibrosis Trust, 2007). The DXA scan will give information on body composition, which can also be used in the assessment of nutritional status (King et al, 2005).
• Normal growth and nutritional status are associated with better lung function and increased survival
• The majority of patients with CF are pancreatic insufficient
• Energy requirements vary and should be assessed individually
• A normal to high fat diet should be encouraged
• Regular advice from an experienced CF dietitian should be provided
• A four to five day dietary and enzyme diary should be recorded every one to two years or more frequently if growth is poor
• Growth and nutritional status should be determined at every visit
• All patients over the age of ten years should have a bone scan (DXA) repeated at least every three years depending on the scan results
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