Cystic Fibrosis: Nutritional Considerations
Nutritional management has a dramatic effect on growth and survival in patients with CF, but is often challenging due to malabsorption. Survival is markedly poorer in patients who are underweight for their height. Thus, a high-energy diet is commonly recommended, along with nutritional supplements.4
Maintenance of a high-calorie diet is a cornerstone of therapy. A study of adults with CF found that 60% failed to meet recommended calorie needs, and 72% failed to meet recommendations for both protein and energy.5 Patients with CF are susceptible to weight loss for several reasons, including ongoing steatorrhea and azotorrhea (despite enzyme therapy); a 10% to 30% increase in elevated resting energy expenditure (REE), particularly during pulmonary exacerbations; treatment with bronchodilators (which cause an 8% to20% increase in REE)6; infection-related anorexia; gastrointestinal disturbances; and clinical depression.4
With proper nutrition therapy, including an energy intake of 120% to 150% of the Recommended Dietary Allowance (RDA), patients with CF may grow normally. Although nutritional supplements have been used in an attempt to attain this goal, research does not support their efficacy.7 Instead, high-fat diets have typically been used,4 although this approach may increase the susceptibility of CF patients to oxidative stress.8 The kind of fat that should be given is also under debate (see below).
Provision of a diet high in essential fatty acids helps with weight and prevention of deficiency symptoms. Biochemical evidence of deficiency of both the essential omega-6 fatty acid linoleic acid and a derivative of the essential omega-3 essential fatty acid alpha-linolenic acid (docosahexanoic acid) is common in patients with CF, although clinical signs and symptoms are rare.9
Although a diet high in fat (including animal fat) is often recommended, it has disadvantages for patients with CF. The omega-6 fatty acid arachidonic acid found in these foods may adversely affect CF patients by contributing to oxidative stress and a pro-inflammatory effect in lung tissue through an increase in leukotriene B4.8 Omega-3 fats, however, appear to be of clinical benefit in patients with CF. Reduction of sputum volume, improved lung function, and a decrease in leukotriene B4 and in use of antibiotics have been observed in EPA/DHA-supplemented patients.4,10 Increasing the intake of plant sources of omega-3 fats (alpha-linolenic acid) and monounsaturated fats has been suggested as an alternative approach to improving fatty acid nutrition in CF patients.4 The Cystic Fibrosis Foundation consensus panel has made similar recommendations, suggesting that oils rich in both omega-3 and monounsaturated fats (eg, flax, canola, soy) benefit CF patient.9
Patients should be monitored for evidence of vitamin deficiency and treated accordingly. Patients with CF require supplemental nutrients for various reasons. The fat-soluble vitamins A, D, E, and K are a priority, mainly because pancreatic enzyme insufficiency often results in malabsorption of these nutrients. Oxidative stress occurs to a greater degree in patients with CF than in healthy controls.8 Consequently, deficiencies of antioxidants (eg, vitamin C) and low concentrations of antioxidant enzymes (eg, glutathione peroxidase) have been found in patients with CF, along with poor selenium and zinc status.4 Patients with CF are also often iron deficient, may not take in recommended amounts of calcium, and are at risk for hyponatremia due to salt loss through the skin.9 The amounts of vitamins required in supplements follow.
Vitamin A and carotenoids. Deficiency of vitamin A occurs in 15% to 40% of CF patients,9 in spite of enzyme replacement and use of low-dose vitamin A supplements (2500-4000 IU/day). Supplementation of up to 12000 IU of vitamin A per day may become necessary to normalize plasma levels.4 Carotenoids are also malabsorbed in CF patients, and lycopene, alpha-carotene, and beta-carotene concentrations appear significantly lower than in age-matched controls.11 Supplemental beta-carotene decreases markers of oxidative stress in CF patients.4
Vitamin D. Deficiency of vitamin D occurs in 10% to 40% of children with CF, and in more than 81% of adults with this condition, especially at northern latitudes.12 Lack of vitamin D aggravates the already greater risk for osteoporosis and fractures seen in CF patients.9 Low concentrations of vitamin D have been found in patients with CF taking 1000 IU of vitamin D per day,4 and the deficiency appears not to be corrected even with megadoses of the vitamin.12 For increasing calcium absorption and bone density and decreasing markers of bone resorption, the active hormone (D3) form of vitamin D and vitamin D analogues appear more effective.13
Vitamin E. Deficiency of vitamin E occurs in 87% of unsupplemented patients with CF, prompting supplementation of 200 mg/day.4 Low serum levels are common despite supplementation.4,9
Vitamin K. Deficiency of vitamin K has been found in 81% of patients with CF. While vitamin K supplements (0.1-0.3 mg/day) reduced a sensitive indicator of vitamin K status, the number of persons found to be deficient decreased by only 50%.14 Increasing the dose to 1 mg/day resulted in normalization of vitamin K status.15
Nutrition consultation to assess nutrient status, advise patient in dietary change, and arrange follow-up. The diet should be individualized based on clinical status.
Exercise prescription: Patient-specific aerobic and resistance training.
What to Tell the Family
Cystic fibrosis is an inherited lung disease that frequently causes respiratory tract infection, resulting in poor appetite and weight loss. Poor absorption of nutrients is common, requiring pancreatic enzyme replacement and supplements of fat-soluble (and possibly water-soluble) vitamins. Patients with CF should follow a high-calorie, high-fat, nutrient-dense diet to help meet needs for energy, growth, and vitamins and minerals. Additional supplementation with fatty acids and minerals may be required if clinical examination or laboratory studies indicate a state of deficiency or insufficiency. Long-term complications of CF that may be delayed through proper diet, exercise, and medical care include osteoporosis, diabetes, and accelerated loss of pulmonary capacity.
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