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Cystic fibrosis: Nutritional consequences and management

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Life expectancy for patients with Cystic Fibrosis (CF) has steadily improved during the last three decades, and death in childhood is now uncommon. Nutrition is a critical component of the management of CF, and nutritional status is directly associated with both pulmonary status and survival. Expert dietetic care is necessary, and attention must be given to ensuring an adequate energy intake in the face of demands which may be increased by inadequately controlled malabsorption, chronic broncho-pulmonary colonisation by bacteria and fungi, exacerbations of acute lung infection, impaired lung function, and the need for rehabilitation, repair and growth.

Pancreatic enzyme replacement therapy (PERT) is needed by up to 90% of CF patients in Northern Europe, where the ‘severe’ mutation ΔF508 predominates, but a smaller proportion in Mediterranean countries and elsewhere, because pancreatic insufficiency is one of few features of CF which correlate with genotype.

Complications of CF including liver disease and CF-related diabetes pose further challenges. In addition, deficiency of specific nutrients including fat soluble vitamins (particularly A, E and K) essential fatty acids and occasionally minerals occur for a variety of reasons. Osteopenia is common and poorly understood. Liver disease increases the likelihood of vitamin D deficiency. Glucose intolerance and diabetes affect at least 25% of CF adults, and the diabetes differs from both types 1 and 2 diabetes mellitus, but it inversely correlates with prognosis.

Management consists of anticipating problems and addressing them vigorously as soon as they appear. Supplements of vitamins are routinely given. Energy supplements can be oral, enteral or, rarely, parenteral. All supplements, including PERT, are adjusted to individual needs.

Section snippets

Pathophysiology of nutritional deficits

Cross-sectional data from the UK Cystic Fibrosis register showed that the mean height and weight standard deviation (Z) scores of both male and female CF children were significantly below those of the general population during the first decade of life, after which there was a progressive decline in both parameters. Body Mass Index (BMI), was however maintained around normal in young children, indicating that they were small but not wasted, but again it became progressively lower with age,

Essential fatty acid deficiency

A deficiency of essential fatty acids (EFA) has been described in CF patients that is characterised by a decrease in plasma levels of linoleic acid (LA) and docosahexaenoic acid (DHA) with an increase in the level of eicosatrienoic acid.61 EFA deficiency is not due simply to impaired lipid absorption secondary to pancreatic insufficiency, since it has also been described in patients with normal nutritional status and pancreatic function.23

Lipid peroxidation of the long chain polyunsaturated

Management

The interaction of the various factors regulating energy balance is clearly complex, and some CF patients seem to maintain body weight for lengthy periods even though their reported energy intake is apparently less than ‘optimal’, i.e. less than the 120–150% of the recommended daily allowance traditionally advised. However, it is essential to keep all CF patients under close nutritional surveillance, and regular assessment by the dietitian is important. Management must be individualised, and

Pancreatic enzyme replacement therapy (PERT)

All patients who are pancreatic insufficient (PI), as shown by fat balance studies and/or indirect pancreatic function tests such as faecal elastase63, 64 or chymotrypsin, should receive pancreatic enzyme supplements. By far the most effective formulations are enteric coated granules or microspheres, which resist inactivation by gastric acid. Even so, because of failure of pancreatic bicarbonate secretion, the pH of the duodenum is often well below the level at which the enzymes—mainly lipase

Oral supplements

When nutritional intervention needs to be stepped up (Table 1), there is a wide range of oral supplements from which to choose. Simple energy-dense supplements are the most palatable, and, therefore, encourage adherence, but may prove to be used as food substitutes rather than true supplements, in which case the fact that they tend to be relatively low in protein may be a theoretical disadvantage. Nevertheless, if properly used they can produce a worthwhile degree of weight gain36 and in some

Enteral nutrition

If oral supplements, whether simple calorie boosters or more nutritionally complete, fail to correct the problem, the next step is enteral nutrition. If it is anticipated that only a short period of treatment will be needed, for example during recovery from a severe respiratory exacerbation, or from surgery, or before elective surgery, feeds can be given by naso-gastric tube. This is not liked by patients, but even when it is clear that long-term enteral feeding will be needed some will accept

Parenteral nutrition

Parenteral nutrition is efficient in improving nutritional status in malnourished CF patients.54 However, it is a very invasive, complex and expensive treatment, the use of which should be restricted to very few patients with severe malnutrition when enteral nutrition has failed or is impossible to perform, such as in patients awaiting lung or liver transplantation in a very poor pulmonary and nutritional condition, or in infants with short gut syndrome following neonatal surgery.

Although

Vitamins and minerals

Guidelines for vitamin and mineral supplementation are available in the European consensus on nutrition in CF patients6 (Table 3).

Vitamins

Vitamin supplementation should be adjusted as necessary according to blood levels. The serum level of vitamin A is negatively associated with C-reactive protein and other evidence of inflammation, and it is important to distinguish between low serum levels secondary to inflammatory processes and those due to poor nutritional stores.68 If blood levels of vitamin A remain low despite adequate supplementation, attention should be given to patient compliance and the retinol binding protein and zinc

Minerals

Because of the increased loss of sodium and chloride in sweat, daily supplementation of salt on an individual basis should be given during fever, vigorous exercise or high environmental temperature. Supplementation of iron, zinc or selenium is only necessary when there is biochemical evidence of deficiency.

Conclusions

Maintenance of a normal nutritional status is an important task for the multidisciplinary team managing patients with CF. It is made more difficult with increasing age, chronic colonisation with Pseudomonas aeruginosa and the onset of progressive respiratory failure.

A stepwise management programme is necessary, starting with boosted oral nutrition and progressing as necessary to oral supplementation, enteral nutrition and, rarely parenteral nutrition. The amount and type of caloric

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