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Cystic Fibrosis: Nutritional Considerations
Nutritional management has a dramatic effect on growth and survival
in patients with CF. The following considerations are key:
- Sufficient caloric intake: Survival is much
better in patients who are nearer their normal weight. A study
of adults with CF found that 60 percent failed to meet recommended
calorie needs, and 72 percent failed to meet recommendations for
both protein and calories. Thus, a high-energy diet is commonly
recommended, along with nutritional supplements.
With proper nutrition therapy, including a calorie intake of 20
to 50 percent more than the Estimated Energy Requirement (EER),
patients with CF may grow normally. Although nutritional supplements
have been used in an attempt to attain this goal, research does
not support their use. Instead, high-fat diets have typically been
used, although the benefit of this approach is not yet been proven
either. The kind of fat that should be consumed is also under debate.
Although a diet high in fat (including animal
fat) is often recommended, it has disadvantages for patients with
CF. The omega-6 fatty acids found in these foods may adversely
affect CF patients by encouraging inflammation in the lungs.
In contrast, omega-3 fats appear to be of clinical benefit in patients
with CF. Reduction of sputum, improved lung function, a decrease
in inflammation, and a decreased need for antibiotics have been
observed in patients who have taken omega-3 fatty acid supplements.
Increasing the intake of plant sources of omega-3 fats (e.g., flax
seed and flax oil) and monounsaturated fats (e.g., olive oil) has
been suggested as an approach to improving fatty acid nutrition
in CF patients. The Cystic Fibrosis Foundation consensus panel
has made similar recommendations, suggesting that oils rich in
both omega-3 and monounsaturated fats (e.g., flax, canola, and
soy) benefit CF patients.
- Nutritional adequacy: Patients should be monitored
for evidence of vitamin deficiency and treated accordingly. CF
patients require supplemental nutrients for various reasons. The
fat-soluble vitamins A, D, E, and K are a priority, mainly because
digestive enzyme insufficiency often results in poor absorption
of these nutrients.
Deficiencies of antioxidants (e.g., vitamin C) and low concentrations
of antioxidant enzymes (e.g., glutathione peroxidase) have been
found in CF patients, along with low levels of selenium and zinc.
CF patients are also at risk for low levels of iron, calcium, and
sodium.
- Vitamin A and carotenoids
Deficiency of vitamin
A occurs in 15 to 40 percent of CF patients, in spite of enzyme
replacement and use of low-dose vitamin A supplements (2,500
to 4,000 International Units, or IU, a day). Supplementation
of up to 12,000 IU of vitamin A per day may become necessary.
Carotenoids are also poorly absorbed in CF patients, and lycopene,
alpha-carotene, and beta-carotene concentrations appear significantly
lower than in healthy patients.
- Vitamin D
Deficiency of vitamin D occurs in 10 to 40 percent of
children with CF, and in more than 81 percent of adults with
this condition. Lack of vitamin D aggravates the already greater
risk for osteoporosis and fractures seen in CF patients. Low
concentrations of vitamin D have been found in patients with
CF taking 1,000 IU of vitamin D per day, and the deficiency may
not even be completely corrected even with megadoses of the vitamin.
- Vitamin E
Deficiency of vitamin E occurs in 87 percent of unsupplemented
patients with CF. The amount suggested for supplementation is
200 milligrams a day.
- Vitamin K
Deficiency of vitamin K has been found in 81 percent of
patients with CF. Vitamin K supplementation of 1 milligram a day
is recommended.
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