Malnutrition in cystic fibrosis

Malnutrition in CF is multifactorial and has been reviewed in detail elsewhere⁽Reference Pencharz and Durie⁸⁾. There has been evidence of strong links between improved nutritional status and survival for >30 years. A study that compared patients of two North American CF clinics, one of which treated patients with the then traditional low-fat diet and the second treated patients with a high-fat diet, has found the patients treated with a high-fat diet to be taller and heavier⁽Reference Corey, McLaughlin and Williams³⁾. Importantly, this improvement in nutritional status was deemed to be the main reason for a 9-year survival advantage. Since this early study a poor nutritional status has been shown to independently contribute to prognosis⁽Reference Beker, Russek-Cohen and Fink^9–Reference Stern, Wiedemann and Wenzlaff¹¹⁾. Growth failure⁽Reference Beker, Russek-Cohen and Fink⁹⁾ and wasting⁽Reference Sharma, Florea and Bolger¹⁰⁾ are both highly significant independent prognostic indicators of survival. In patients with height <5th percentile at age 5 years risk of death is significantly increased (males P<0·02, females P<0·0001); this increased risk persists at age 7 years (males P<0·01, females P<0·0001)⁽Reference Beker, Russek-Cohen and Fink⁹⁾. Patients with >85% ideal body weight have a better prognosis at 5 years of age than those with <85% ideal body weight (P<0·0001)⁽Reference Sharma, Florea and Bolger¹⁰⁾.

There is also a positive association between nutritional status and lung function⁽Reference Steinkamp and Wiedemann^12–Reference Pedreira, Robert and Dalton¹⁶⁾. Conversely, malnutrition results in poor growth, impaired respiratory muscle function⁽Reference Zemel, Jawad and FitzSimmons¹³⁾, decreased exercise tolerance and immunological impairment that results in increased susceptibility to infections⁽Reference De Meer, Gulmans and van der Laag¹⁷⁾.

Nutritional management

The aims of the nutritional management of CF are that children and adults should be adequately nourished, have normal weight, height, body composition and pubertal development and have optimal vitamin, antioxidant and essential fatty acid status. With increased life expectancy there are constantly new nutritional challenges emerging. Early identification of conditions such as CFRD that may impact on nutritional status is extremely important and good diabetic control is increasingly important. Dietary management should also aim to minimise the nutritional risks associated with the development of reduced bone mineral density. It is therefore essential that dietetic management is an integral part of CF care for all patients.

Pancreatic insufficiency usually develops in infancy and approximately 92% of individuals with CF are pancreatic insufficient by 1 year of age⁽Reference Bronstein, Sokol and Abman¹⁸⁾. Approximately 95% of patients in northern Europe will eventually be pancreatic insufficient as a result of an inadequacy of their own pancreatic enzyme secretions⁽Reference Littlewood, Wolfe and Conway¹⁹⁾. With the introduction of newborn screening within the UK and the early identification of milder mutations the percentage of patients with pancreatic sufficiency may increase. In pancreatic insufficiency there is insufficient pancreatic function to achieve normal digestion and absorption of fat. These patients need to take pancreatic enzyme-replacement therapy in order to prevent the symptoms of fat malabsorption. These symptoms include frequent pale, oily and offensive stools, abdominal pain, poor growth and malnutrition and deficiencies of the fat-soluble vitamins and essential fatty acids.

In individuals with CF malabsorption is secondary to pancreatic insufficiency. However, this representation is oversimplistic, especially if compared with patients with pancreatitis for whom malabsorption is relatively easy to control on low doses of pancreatic enzymes. In patients with CF a host of other factors contribute to malabsorption, including a deficiency of pancreatic bicarbonate that reduces duodenal pH⁽Reference Robinson, Smith and Sly²⁰⁾, an increased loss of bile salts in the stool⁽Reference Walters and Littlewood²¹⁾, an imbalance in the type of bile salts produced⁽Reference Roy, Weber and Morin²²⁾, abnormal ion transfer in the gut as a result of the basic defect in the CFTR⁽Reference Sinaasappel²³⁾, impaired mucosal uptake and transport of long-chain fatty acid across the gut wall⁽Reference Kalivianakis, Minich and Bijleveld^24, Reference Laiho, Gavin and Murphy²⁵⁾ and altered gut motility⁽Reference Gregory²⁶⁾.

All patients who are pancreatic insufficient must take pancreatic enzymes with all food and drinks that contain fat. There are various enzyme preparations available⁽Reference Littlewood, Wolfe and Conway¹⁹⁾. The enteric-coated acid-resistant microsphere and minimicrosphere preparations (e.g. Creon®Micro and Creon® 10 000 (Solvay Healthcare, Southampton, Hants., UK) and Nutrizym 10® (Merck Serono, Feltham, Middx, UK)) are more effective than the older pancreatic enzyme preparations (e.g. Pancrex V® (Paines & Byrne Ltd, Staines, Middx, UK) and Cotazym® (Organon Pharmaceuticals, West Orange, NJ, USA)). As a result of the multiple factors affecting enzyme efficacy dose requirements can vary between 400 IU/g fat and 5000 IU/g fat⁽Reference Littlewood, Wolfe and Conway¹⁹⁾. The dose of enzymes required with all meals, snacks and drinks is titrated against the fat content of the food. Foods that do not contain fat do not need enzymes. The enzymes must not be crushed or chewed, because their efficacy will be reduced. Enzymes should be given at the beginning, middle and end of the meal, especially if the meal takes >30 min to eat. Doses should be advised individually and re-assessed regularly by the dietitian. The dose is adjusted according to clinical symptoms, appearance of the stools and objective assessment of weight gain, nutritional status, growth and absorption. It is recommended that the total dose of enzymes should not usually be >10 000 IU lipase/kg body weight per d⁽²⁷⁾. Educating patients about dose adjustment and the timing of pancreatic enzyme-replacement therapy is essential to achieve optimal absorption and a good nutritional status. Individuals with CF should be encouraged to openly discuss any adherence issues or problems they experience with pancreatic enzyme-replacement therapy.

Fat-soluble vitamins

Exocrine pancreatic insufficiency and altered bile salt metabolism are two factors contributing to fat malabsorption and fat-soluble vitamin deficiency in most individuals with CF. Biochemical evidence of fat-soluble vitamin deficiency has been found as early as 2 months of age in untreated screened infants with CF⁽Reference Feranchak, Sontag and Wagener²⁸⁾. All patients should have plasma levels of the fat-soluble vitamins A, D and E, total cholesterol, vitamin E:cholesterol and a prothrombin time checked at least annually^(29, Reference Sinaasappel, Stern and Littlewood³⁰⁾. Ideally, this check should be carried out at a time of clinical stability. Retinol-binding protein, plasma Zn levels and C-reactive protein should be measured at the same time to help in the interpretation of plasma vitamin A levels^(29, Reference Christian and West³¹⁾. Vitamin K status is more difficult to assess. Plasma vitamin K levels alone are unreliable for assessment of vitamin K status⁽Reference Durie^32, Reference Rashid, Durie and Andrew³³⁾. Vitamin K deficiency of the liver and bone may occur independently. Prothrombin levels are the easiest way to assess vitamin K deficiency; however, they do not always correlate with plasma vitamin K levels⁽Reference De Montalembert, Lenoir and Saint-Raymond³⁴⁾. Although it is not widely available, protein induced by vitamin K absence or antagonist-II levels are a more sensitive measure of vitamin K status of the liver⁽Reference Alexander, Marcus and Green³⁵⁾. Undercarboxylated osteocalcin is the most accurate method of assessing vitamin K adequacy for bone metabolism but it is not used routinely in clinical practice.

All patients with pancreatic insufficiency should receive supplementation with the fat-soluble vitamins A, D and E. There is little international consensus about the need for routine vitamin K supplementation, although it is likely that all patients with CF need routine vitamin K supplementation for optimal bone health. Optimal supplementary doses of the fat-soluble vitamins have not been adequately established and vary from country to country^(29, Reference Sinaasappel, Stern and Littlewood³⁰⁾. Frequent and serial monitoring of serum vitamin levels is essential⁽Reference Feranchak, Sontag and Wagener²⁸⁾ and doses should be adjusted based on these results. Patients who are pancreatic sufficient need to be monitored annually to ensure that plasma vitamin levels are adequate. Most, if not all, patients who are pancreatic sufficient will require supplementation with vitamin D to achieve adequate levels for optimal bone health.

For adults, starting doses for supplementation are (/d): vitamin A 1200–3000 μg, vitamin D 10–20 μg and vitamin E 100–400 mg⁽Reference Sinaasappel, Stern and Littlewood³⁰⁾.

Nutritional support

International consensus reports recommend constant monitoring of nutritional status and growth with staged nutritional intervention for individuals with CF who have or are at risk of nutritional failure and malnutrition^(29, Reference Sinaasappel, Stern and Littlewood³⁰⁾. The actual extent of nutritional failure for initiating interventions varies between these reports^(29, Reference Sinaasappel, Stern and Littlewood³⁰⁾. It is recommended that individuals with CF have access to a CF specialist dietitian at every outpatient clinic visit, inpatient admission and at the time of annual review^(64, Reference Kerem, Conway and Elborn⁶⁵⁾.

Preventative nutritional counselling is recommended for all patients regardless of their nutritional and clinical status. If a patient's weight gain or nutritional status is inadequate or appetite poor, oral dietary supplements are introduced to help to improve energy intake. Supplements are prescribed on an individual basis dependent on the patient's age, preferences and requirements. Supplements should be taken in addition to normal food to increase total daily energy intake and should not replace a meal. It is essential that pancreatic enzyme-replacement therapy is given with all fat-containing supplements. A UK multicentre longitudinal study has shown that their use can promote weight gain⁽Reference Skypala, Ashworth and Hodson⁶⁶⁾ and improvements in protein and energy intake⁽Reference White, Morton and Peckham^67, Reference Poustie, Russell and Watling⁶⁸⁾. The efficacy of the short-term use of oral energy supplements in the acute situation, and the long-term use in adults or those with advanced lung disease, has not been fully assessed⁽Reference Smyth and Walters⁶⁹⁾.

If preventative nutritional counselling and/or oral dietary supplements fail to prevent or reverse poor nutrition or nutritional decline, enteral tube feeding is the final recommended stage of nutritional support. The European and UK nutrition consensus documents give specific recommendations on when enteral tube feeding should be initiated^(29, Reference Sinaasappel, Stern and Littlewood³⁰⁾. These criteria are taken as an indication of the need to introduce enteral tube feeding, but a more comprehensive global nutritional and clinical assessment may prompt or delay intervention. Some of the additional factors that may be taken into consideration are summarised in Table 1.

Table 1. Examples of objective and subjective factors taken into consideration when assessing patients for the introduction of enteral tube feeding

There are no randomised controlled trials that have assessed the efficacy or possible adverse effects of enteral tube feeding in CF⁽Reference Conway, Morton and Wolfe⁷⁰⁾. However, enteral tube feeding has been shown to improve weight gain and nutritional status⁽Reference Jelalian, Stark and Reynolds^71, Reference Rosenfeld, Casey and Pepe⁷²⁾ and to stabilise⁽Reference Efrati, Mei-Zahav and Rivlin⁷³⁾ or slow the rate of decline in respiratory function⁽Reference Walker and Gozal^74, Reference Williams, Ashworth and McAlweenie⁷⁵⁾. Improvement in respiratory function has been shown following 1 year of enteral tube feeding⁽Reference Steinkamp and von der Hardt⁷⁶⁾. Improved nutritional status may also contribute to increased quality of life⁽Reference Gunnell, Christensen and McDonald⁷⁷⁾. Early discussion about enteral tube feeding and early introduction of enteral tube feeding is essential, as early intervention is associated with improved outcome⁽Reference Walker and Gozal^74, Reference Oliver, Heine and Hang Ng⁷⁸⁾. Those patients with advanced disease may benefit less⁽Reference Oliver, Heine and Hang Ng^78, Reference Van Biervliet, De Waele and Van Winckel⁷⁹⁾. Although patients may express concerns about body image⁽Reference Abbott, Morton and Musson⁸⁰⁾, positive attitudes to gastrostomy placement including increased quality of life have also been reported⁽Reference Gunnell, Christensen and McDonald⁷⁷⁾.

Feeds are usually administered overnight and patients are encouraged to eat normally through the day. Most patients tolerate whole-protein polymeric feeds with a high energy density. Enteral tube feeding may precipitate hyperglycaemia requiring insulin therapy⁽Reference Smith, Clarke and Stableforth⁸¹⁾ irrespective of the carbohydrate content of the feed⁽Reference Kane and Black⁸²⁾. This tendency is exacerbated if the patient is also receiving corticosteroids; therefore, the introduction of enteral tube feeding should be closely monitored to assess its effects on nocturnal glycaemia.

Cystic fibrosis-related diabetes

With increased longevity CFRD has emerged as the most common co-morbidity in CF^(83, Reference Moran, Hardin and Rodman⁸⁴⁾. The reported prevalence varies depending on the screening and diagnostic criteria used⁽Reference O'Riordan, Robinson and Donaghue⁸⁵⁾. The prevalence of CFRD increases with age, with 26% of 10–20 year olds⁽Reference Moran, Doherty and Wang⁸⁶⁾ and 50% of 30 year olds⁽Reference Lanng, Thorsteinsson and Pociot⁸⁷⁾ being reported as having CFRD. In addition, glucose intolerance is common in both adolescent and adult patients with CF⁽Reference Moran, Hardin and Rodman⁸⁴⁾ and glucose tolerance status⁽Reference Lanng, Hansen and Thorsteinsson⁸⁸⁾ and insulin resistance can fluctuate. Consequently, patients may be glucose intolerant or diabetic for a period of time and then revert to normal again⁽Reference Lanng, Hansen and Thorsteinsson⁸⁸⁾. This fluctuation requires a unique approach to diagnosis and management.

Conventional measures of glucose status used in the diagnosis of diabetes in the general population are often unreliable in CFRD. Fasting glucose levels do not reliably identify CFRD⁽Reference Lanng⁸⁹⁾ even if impaired fasting glucose is used as an indication for an oral glucose tolerance test⁽Reference Mueller-Brandes, Holl and Nastoll⁹⁰⁾. HbA_1c has been used as a screening test but has been shown to be unreliable in the diagnosis of CFRD⁽Reference Lanng, Hansen and Thorsteinsson⁸⁸⁾ as levels are often normal at the time of diagnosis of CFRD. Symptoms are unreliable as the onset of CFRD is insidious and patients are usually asymptomatic. The 2 h oral glucose tolerance test is the recommended screening test for CFRD⁽Reference O'Riordan, Robinson and Donaghue^85, Reference Lanng, Hansen and Thorsteinsson^{88, 91)}. Importantly, CFRD is distinct from type 1 or type 2 diabetes but has features of both. It is associated with insulinopenia and insulin resistance⁽Reference Hardin, LeBlanc and Para^92, Reference Hardin, LeBlanc and Marshall⁹³⁾. Ketoacidosis is unusual but can occur, especially if there has been a long period of symptomatic hyperglycaemia before diagnosis⁽Reference Moran, Doherty and Wang⁸⁶⁾.

There are many factors specific to CF, including acute and chronic respiratory infection and inflammation, increased energy expenditure, malabsorption, abnormal intestinal transit time, malnutrition, glucagon deficiency, CF-related liver disease, overnight tube feeding and steroid use, that may contribute to fluctuations in glucose tolerance status.

CFRD mainly occurs in individuals with the most severe CF mutations, all of which are associated with exocrine pancreatic insufficiency⁽Reference Rosenecker, Eichler and Kuhn^94–Reference Adler, Shine and Chamnan⁹⁶⁾, and it is more common in those patients who are homozygous for the delta F508 genotype⁽Reference Marshall, Butler and Stoddard⁹⁷⁾. Patients with milder genetic mutations associated with pancreatic sufficiency are less likely to develop CFRD⁽Reference Zielenski and Tsui^5, Reference Adler, Gunn and Haworth^95, Reference Ahmed, Corey and Forstner⁹⁸⁾. Other risk factors for the development of CFRD include increasing age⁽Reference Rosenecker, Eichler and Kuhn^94, Reference Adler, Shine and Chamnan^96, Reference Marshall, Butler and Stoddard⁹⁷⁾, female gender⁽Reference Rosenecker, Eichler and Kuhn^94, Reference Adler, Shine and Chamnan^96, Reference Marshall, Butler and Stoddard⁹⁷⁾, more severe pulmonary disease⁽Reference Adler, Shine and Chamnan^96, Reference Marshall, Butler and Stoddard⁹⁷⁾, liver disease⁽Reference Rosenecker, Eichler and Kuhn^94–Reference Adler, Shine and Chamnan⁹⁶⁾, use of corticosteroids⁽Reference Adler, Gunn and Haworth^95, Reference Adler, Shine and Chamnan⁹⁶⁾, use of enteral tube feeding⁽Reference White, Pollard and Etherington⁹⁹⁾ and organ transplantation⁽Reference Adler, Gunn and Haworth^95, Reference Hadjiliadis, Madill and Chaparro^100, Reference Navas de Solis, Merino Torres and Mascarell Martinez¹⁰¹⁾.

Early detection and treatment of CFRD is important as there is increased morbidity in the pre-diabetic state. Insulin deficiency leads to poorer pulmonary outcome⁽Reference Koch, Rainisio and Madessani¹⁰²⁾. The early diagnosis and intervention in CFRD can have a profound impact on patient well-being, protecting against weight loss and deterioration in lung function⁽Reference Lanng, Thorsteinsson and Nerup¹⁰³⁾. The negative impact of diabetes on pulmonary status in CF appears to be greater in female patients than in males⁽Reference Milla, Billings and Moran^104, Reference Sims, Green and Mehta¹⁰⁵⁾. Women with CFRD have a survival disadvantage⁽Reference Milla, Billings and Moran¹⁰⁴⁾. The negative impact of diabetes on nutritional decline appears to be more pronounced in those patients who are still growing during the pre-diabetic years⁽Reference White, Pollard and Etherington⁹⁹⁾. This factor is particularly important as these patients are likely to be going through the difficult phase of transition from paediatric to adult services. CFRD is associated with a more rapid rate of decline in lung function even before diagnosis⁽Reference Lanng, Thorsteinsson and Nerup^103, Reference Costa, Potvin and Hammana¹⁰⁶⁾, although this decline can be prevented through the use of intensive nutritional intervention⁽Reference White, Pollard and Etherington⁹⁹⁾.

The importance of early detection and good control of CFRD cannot be overemphasised. Microvascular complications are increasingly recognised in patients with CFRD⁽Reference Lanng, Thorsteinsson and Lund-Andersen^107–Reference Van den Berg, Morton and Kok¹¹¹⁾. Although macrovascular complications have not yet been reported, with the increasing life expectancy of individuals with CF the risk of these complications developing will be minimised with good control.

The primary aim of treatment in CFRD is to maintain nutritional status, and the maintenance of a high-fat high-energy diet is important. Insulin therapy is the treatment of choice to help maintain an adequate energy intake. All patients should receive individualised dietary review and advice at the time of the diagnosis of CFRD. They should usually maintain a high-energy diet and the insulin dose should be tailored to their individual requirements.

Individuals should be advised not to limit their intake of refined carbohydrates, or high-fat foods^(91, Reference Wilson, Kalnins and Stewart¹¹²⁾. Many individuals are aware of the dietary restrictions (reduced fat, high fibre, low sugar, low salt, controlled energy) that are part of the treatment of type 1 and type 2 diabetes and these restrictions are directly opposed to the requirements for CFRD (a high-fat high-energy high-protein diet with an increased Na content). Many individuals with CF have erratic eating habits and their insulin regimen should be tailored to their pattern of eating. They should not decrease their carbohydrate intake but should be encouraged to eat regular meals with similar carbohydrate content each day. If this approach compromises their total energy intake, carbohydrate counting may be valuable, enabling them to eat as much as they can. If a patient is receiving bolus nasogastric or gastrostomy feeds over a few hours they can be covered with soluble insulin⁽Reference Moran, Hardin and Rodman^{84, 91)}. Intermediate or long-acting insulin will be required for overnight feeds. Relatively large doses of insulin may be required for feeds, and patients and carers must be made aware of the risk of severe hypoglycaemia if the insulin is given and the feed then not being delivered or if the feed is discontinued⁽Reference Moran, Hardin and Rodman^{84, 91)}.

The additional burden of CFRD needs to be acknowledged in patient management and care. In addition, there needs to be consideration of transition to a second care provider, that of the Diabetes Service, which may be less well established.

Bone health

Reduced bone mineral density is well documented in adolescents and adults with CF⁽Reference Haworth, Selby and Webb^113, Reference Conway, Morton and Oldroyd¹¹⁴⁾. Most patients with severe CF-related lung disease have reduced bone mass⁽Reference Shane, Silverberg and Donovan^115, Reference Aris, Renner and Winders¹¹⁶⁾. Recent reports suggest that defective bone mineralisation occurs in early childhood in individuals with CF⁽Reference Sermet-Gaudelus, Souberbielle and Ruiz^51, Reference Douros, Loukou and Nicolaidou¹¹⁷⁾. Prevalence data vary depending on the population studied and method of assessment used.

The aetiology of low bone mineral density in CF is a complex interaction of multiple factors that include the effect of the CFTR mutation itself, poor nutritional status including low BMI, deficiency of the fat-soluble vitamins D and K, poor Ca intakes, disease severity, recurrent chest infections with raised levels of circulating pro-inflammatory cytokines, delayed puberty, secondary hypogonadism, CFRD, reduced weight-bearing exercise and physical inactivity, treatment with corticosteroids or other drugs that cause bone loss such as depot medroxyprogesterone acetate and immunosuppressive therapy⁽Reference Aris, Merkel and Bachrach⁵⁴⁾.

Bone mineral acquisition in childhood and especially during the pubertal growth spurt, in adolescence, is a major determinant of adult bone health. Of the peak bone mass ≥90% is achieved by the end of the pubertal growth spurt⁽Reference Bailey, McKay and Mirwald¹¹⁸⁾. It is therefore essential that prevention strategies to attain and maintain normal bone status begin from diagnosis, but even greater emphasis on these issues occurs during adolescence. A multidisciplinary approach to prevention is essential and should include optimising respiratory status and encouraging regular weight-bearing exercise. Dietetic management focuses on optimising weight gain and growth and optimising intakes of nutrients that support bone development such as Ca, vitamin D and vitamin K.

Ca is the major mineral in the skeleton. Reduced Ca intake in childhood is linked with an increased risk of osteoporosis in adult life and an increased Ca intake may improve bone mineral density⁽Reference Cadogan, Eastell and Jones¹¹⁹⁾. Girls with CF have marked endogenous faecal Ca loss⁽Reference Schulze, O'Brien and Germain-Lee¹²⁰⁾ and lower bone Ca accretion rates during pre- and late puberty than girls without CF⁽Reference Schulze, Cutchins and Rosenstein¹²¹⁾. Dietetic supervision is essential to ensure an adequate Ca intake.

Vitamin D intake and blood levels should be reviewed at least annually. Low blood vitamin D levels remain common in individuals with CF despite the use of standard (≥20 μg/d) and high-dose replacement regimens⁽Reference Stephenson, Brotherwood and Robert^47–Reference Wolfenden, Judd and Shah⁵²⁾. There is now increased attention on the role of vitamin K in bone health⁽Reference Nicolaidou, Stavrinadis and Loukou⁶²⁾. Vitamins K and D together may postpone fracture risk by 10 years in the non-CF population⁽Reference Vermeer¹²²⁾. Evidence is accumulating that all patients with CF should receive vitamin K supplements (see earlier discussion of vitamin supplementation).

Other nutritional challenges

In addition to the clinical challenges to achieving a good nutritional status in young adults with CF, there are also social pressures. Societal pressure on young women to remain thin and strive to achieve ‘size zero’ may compromise optimum nutritional management. Clinically, the aim is for a BMI of 22 kg/m² in females and 23 kg/m² in males⁽Reference Stallings, Stark and Robinson¹²³⁾. In addition, nationally there is an emphasis on a low-fat high-fibre ‘healthy eating’ regimen that is in direct contrast to the high-fat high-energy dietary recommendations for CF of 120–150% of estimated average requirements for energy with 40% of total energy coming from fat⁽Reference Vaisman, Pencharz and Corey^124, Reference Pencharz, Hill and Archibald¹²⁵⁾.

In view of the importance of nutrition there is often persistent emphasis on weight gain from diagnosis, which may result in issues relating to body image and eating behaviour. Adolescents with chronic illnesses have been reported to be at greater risk for patterns of eating disorders or disordered eating behaviour than other adolescents⁽Reference Jones, Lawson and Daneman^126, Reference Meltzer, Johnson and Prine¹²⁷⁾. Reports in relation to individuals with CF are conflicting⁽Reference Abbott, Morton and Musson^80, Reference Raymond, Chang and Crow^128, Reference Shearer and Bryon¹²⁹⁾. In the author's experience of adolescents and young adults with CF, eating behaviour and attitudes, body satisfaction and self-esteem are similar to those of their healthy peers. Males perceive themselves as heavier than they are but also wish to be heavier still. Females with CF see themselves as thinner than they are but are happy with their perceived body image. Females with CF actually reported fewer problems than their healthy peers⁽Reference Abbott, Conway and Etherington¹³⁰⁾.

However, invasive nutritional support and the presence of CFRD may confound this outcome. No difference has been found between patients with CFRD and adults with CF who do not have CFRD in relation to actual, perceived or desired BMI⁽Reference Abbott, Morton and Musson^80, Reference Abbott, Conway and Etherington¹³¹⁾. However, those with CFRD, especially females, report a greater number of problems concerning food and eating behaviours. In addition, both males and females with CFRD are less satisfied with their body appearance than controls. Patients treated with insulin report greater problems with food and eating behaviours and feelings of lower self-worth than those taking oral medication⁽Reference Abbott, Conway and Etherington¹³¹⁾. Both males and females receiving nutritional interventions (oral supplements or enteral tube feeds) have been found to have appropriate eating behaviours and a desire to gain weight; females receiving nutritional intervention report more dieting behaviour, greater preoccupation with food and feeling more pressure to eat than controls⁽Reference Abbott, Morton and Musson⁸⁰⁾. Adults with CF receiving nutritional interventions, especially tube feeding, have been found to be less satisfied with their body image, report lower self-esteem and poorer quality of life⁽Reference Abbott, Morton and Musson⁸⁰⁾.

The burden of treatment and transition

Increasing and improved survival has occurred as a result of more aggressive management of CF and the introduction of new therapies. Thus, many young adults with CF have a complex regimen of care aimed at both prevention and treatment. For most young adults this regimen requires at a minimum pancreatic enzyme-replacement therapy at every meal and snack, supplemental vitamins, prophylactic oral antibiotic therapy, inhaled and nebulised therapies and oral anti-inflammatory medication. On the other hand, the patient with more complex care may require treatment of co-existing liver disease, insulin therapy for co-existing CFRD, bisphosphonate treatment for CF-related low bone mineral density, O₂ therapy and/or non-invasive ventilation, intravenous antibiotic therapy and enteral tube feeding. With the increasing number and complexities of these therapies there may, for some patients, be a point at which the perceived treatment burden outweighs the benefit of any new or additive therapy, and this situation may affect patient adherence. It is also important to acknowledge that, because of the constant emphasis placed on eating, food and nutritional status, for many individuals with CF eating, which is viewed as just another treatment, is problematic. Understanding and improving adherence in the young adult with CF remains a major challenge.

Adolescents and young adults with chronic conditions share the same social, developmental and emotional needs as their healthy peers. There are many transitions that the young healthy adult has to go through, and these transitions help the individual to become increasingly self sufficient. In addition, individuals with a chronic illness such as CF need to make a transition within the healthcare system from paediatric to adult care.

The National Service Framework for Children, Young People and Maternity Services ⁽¹³²⁾ has highlighted the importance of ensuring safe and effective transition; ensuring a seamless transfer is one of the greatest challenges facing both children's and adult services⁽¹³³⁾. With continually-improving survival increasing numbers of adolescents and young adults with CF are making the transition from paediatric to adult care. This transition is a hugely important milestone for the patient and the family and must be handled sensitively.

This transfer process is a challenge for the patient themselves, for their parents, caregivers and for both the paediatric and adult teams caring for the patients. Patients should be transferred to an adult clinic at approximately the age of 16 years, but the exact timing must be flexible, depending on the health of the patient and individual variations in physical and emotional development⁽Reference Conway¹³⁴⁾.

Different transitional models exist⁽¹³⁵⁾ but successful transition planning and programmes are crucially dependent on collaboration between children's and adult services⁽¹³⁶⁾. It is important that transition is viewed as a process and not a single event. As CF is a multisystem disorder transition may be from more than one service provider, e.g. Liver Service, Endocrine Service as well as the CF Service, and hence may be complex.

A six-step programme for transfer between the paediatric and adult CF Units that aims to reduce any patient anxiety⁽Reference Conway, Brownlee and Peckham¹³⁷⁾ is shown in Table 2; audit and evaluation of this process are ongoing.

Table 2. A six-step programme for transfer between the paediatric and adult cystic fibrosis (CF) units⁽Reference Conway, Brownlee and Peckham¹³⁷⁾

Summary

The nutritional challenges of the young adult with CF are complex. In addition to clinical and nutritional challenges there are many social challenges. Transition to adult care remains a stressful and trying time for patients, parents and caregivers but has to be addressed, as with increasing longevity more patients and families will experience the process. Despite CF being the most common lethal inherited genetic condition affecting the Caucasian population, it remains relatively rare, with approximately 8500 individuals with CF in the UK⁽⁴⁾. Nevertheless, increasing numbers reach adulthood and go through the transitional process. Ensuring a seamless transfer is one of the greatest challenges facing both children's and adult services⁽¹³³⁾.